1PERL5160DELTA(1)       Perl Programmers Reference Guide       PERL5160DELTA(1)
2
3
4

NAME

6       perl5160delta - what is new for perl v5.16.0
7

DESCRIPTION

9       This document describes differences between the 5.14.0 release and the
10       5.16.0 release.
11
12       If you are upgrading from an earlier release such as 5.12.0, first read
13       perl5140delta, which describes differences between 5.12.0 and 5.14.0.
14
15       Some bug fixes in this release have been backported to later releases
16       of 5.14.x.  Those are indicated with the 5.14.x version in parentheses.
17

Notice

19       With the release of Perl 5.16.0, the 5.12.x series of releases is now
20       out of its support period.  There may be future 5.12.x releases, but
21       only in the event of a critical security issue.  Users of Perl 5.12 or
22       earlier should consider upgrading to a more recent release of Perl.
23
24       This policy is described in greater detail in perlpolicy.
25

Core Enhancements

27   "use VERSION"
28       As of this release, version declarations like "use v5.16" now disable
29       all features before enabling the new feature bundle.  This means that
30       the following holds true:
31
32           use 5.016;
33           # only 5.16 features enabled here
34           use 5.014;
35           # only 5.14 features enabled here (not 5.16)
36
37       "use v5.12" and higher continue to enable strict, but explicit "use
38       strict" and "no strict" now override the version declaration, even when
39       they come first:
40
41           no strict;
42           use 5.012;
43           # no strict here
44
45       There is a new ":default" feature bundle that represents the set of
46       features enabled before any version declaration or "use feature" has
47       been seen.  Version declarations below 5.10 now enable the ":default"
48       feature set.  This does not actually change the behavior of "use v5.8",
49       because features added to the ":default" set are those that were
50       traditionally enabled by default, before they could be turned off.
51
52       "no feature" now resets to the default feature set.  To disable all
53       features (which is likely to be a pretty special-purpose request, since
54       it presumably won't match any named set of semantics) you can now write
55       "no feature ':all'".
56
57       $[ is now disabled under "use v5.16".  It is part of the default
58       feature set and can be turned on or off explicitly with "use feature
59       'array_base'".
60
61   "__SUB__"
62       The new "__SUB__" token, available under the "current_sub" feature (see
63       feature) or "use v5.16", returns a reference to the current subroutine,
64       making it easier to write recursive closures.
65
66   New and Improved Built-ins
67       More consistent "eval"
68
69       The "eval" operator sometimes treats a string argument as a sequence of
70       characters and sometimes as a sequence of bytes, depending on the
71       internal encoding.  The internal encoding is not supposed to make any
72       difference, but there is code that relies on this inconsistency.
73
74       The new "unicode_eval" and "evalbytes" features (enabled under "use
75       5.16.0") resolve this.  The "unicode_eval" feature causes "eval
76       $string" to treat the string always as Unicode.  The "evalbytes"
77       features provides a function, itself called "evalbytes", which
78       evaluates its argument always as a string of bytes.
79
80       These features also fix oddities with source filters leaking to outer
81       dynamic scopes.
82
83       See feature for more detail.
84
85       "substr" lvalue revamp
86
87       When "substr" is called in lvalue or potential lvalue context with two
88       or three arguments, a special lvalue scalar is returned that modifies
89       the original string (the first argument) when assigned to.
90
91       Previously, the offsets (the second and third arguments) passed to
92       "substr" would be converted immediately to match the string, negative
93       offsets being translated to positive and offsets beyond the end of the
94       string being truncated.
95
96       Now, the offsets are recorded without modification in the special
97       lvalue scalar that is returned, and the original string is not even
98       looked at by "substr" itself, but only when the returned lvalue is read
99       or modified.
100
101       These changes result in an incompatible change:
102
103       If the original string changes length after the call to "substr" but
104       before assignment to its return value, negative offsets will remember
105       their position from the end of the string, affecting code like this:
106
107           my $string = "string";
108           my $lvalue = \substr $string, -4, 2;
109           print $$lvalue, "\n"; # prints "ri"
110           $string = "bailing twine";
111           print $$lvalue, "\n"; # prints "wi"; used to print "il"
112
113       The same thing happens with an omitted third argument.  The returned
114       lvalue will always extend to the end of the string, even if the string
115       becomes longer.
116
117       Since this change also allowed many bugs to be fixed (see "The "substr"
118       operator"), and since the behavior of negative offsets has never been
119       specified, the change was deemed acceptable.
120
121       Return value of "tied"
122
123       The value returned by "tied" on a tied variable is now the actual
124       scalar that holds the object to which the variable is tied.  This lets
125       ties be weakened with "Scalar::Util::weaken(tied $tied_variable)".
126
127   Unicode Support
128       Supports (almost) Unicode 6.1
129
130       Besides the addition of whole new scripts, and new characters in
131       existing scripts, this new version of Unicode, as always, makes some
132       changes to existing characters.  One change that may trip up some
133       applications is that the General Category of two characters in the
134       Latin-1 range, PILCROW SIGN and SECTION SIGN, has been changed from
135       Other_Symbol to Other_Punctuation.  The same change has been made for a
136       character in each of Tibetan, Ethiopic, and Aegean.  The code points
137       U+3248..U+324F (CIRCLED NUMBER TEN ON BLACK SQUARE through CIRCLED
138       NUMBER EIGHTY ON BLACK SQUARE) have had their General Category changed
139       from Other_Symbol to Other_Numeric.  The Line Break property has
140       changes for Hebrew and Japanese; and because of other changes in 6.1,
141       the Perl regular expression construct "\X" now works differently for
142       some characters in Thai and Lao.
143
144       New aliases (synonyms) have been defined for many property values;
145       these, along with the previously existing ones, are all cross-indexed
146       in perluniprops.
147
148       The return value of "charnames::viacode()" is affected by other
149       changes:
150
151        Code point      Old Name             New Name
152          U+000A    LINE FEED (LF)        LINE FEED
153          U+000C    FORM FEED (FF)        FORM FEED
154          U+000D    CARRIAGE RETURN (CR)  CARRIAGE RETURN
155          U+0085    NEXT LINE (NEL)       NEXT LINE
156          U+008E    SINGLE-SHIFT 2        SINGLE-SHIFT-2
157          U+008F    SINGLE-SHIFT 3        SINGLE-SHIFT-3
158          U+0091    PRIVATE USE 1         PRIVATE USE-1
159          U+0092    PRIVATE USE 2         PRIVATE USE-2
160          U+2118    SCRIPT CAPITAL P      WEIERSTRASS ELLIPTIC FUNCTION
161
162       Perl will accept any of these names as input, but
163       "charnames::viacode()" now returns the new name of each pair.  The
164       change for U+2118 is considered by Unicode to be a correction, that is
165       the original name was a mistake (but again, it will remain forever
166       valid to use it to refer to U+2118).  But most of these changes are the
167       fallout of the mistake Unicode 6.0 made in naming a character used in
168       Japanese cell phones to be "BELL", which conflicts with the
169       longstanding industry use of (and Unicode's recommendation to use) that
170       name to mean the ASCII control character at U+0007.  Therefore, that
171       name has been deprecated in Perl since v5.14, and any use of it will
172       raise a warning message (unless turned off).  The name "ALERT" is now
173       the preferred name for this code point, with "BEL" an acceptable short
174       form.  The name for the new cell phone character, at code point
175       U+1F514, remains undefined in this version of Perl (hence we don't
176       implement quite all of Unicode 6.1), but starting in v5.18, BELL will
177       mean this character, and not U+0007.
178
179       Unicode has taken steps to make sure that this sort of mistake does not
180       happen again.  The Standard now includes all generally accepted names
181       and abbreviations for control characters, whereas previously it didn't
182       (though there were recommended names for most of them, which Perl
183       used).  This means that most of those recommended names are now
184       officially in the Standard.  Unicode did not recommend names for the
185       four code points listed above between U+008E and U+008F, and in
186       standardizing them Unicode subtly changed the names that Perl had
187       previously given them, by replacing the final blank in each name by a
188       hyphen.  Unicode also officially accepts names that Perl had
189       deprecated, such as FILE SEPARATOR.  Now the only deprecated name is
190       BELL.  Finally, Perl now uses the new official names instead of the old
191       (now considered obsolete) names for the first four code points in the
192       list above (the ones which have the parentheses in them).
193
194       Now that the names have been placed in the Unicode standard, these
195       kinds of changes should not happen again, though corrections, such as
196       to U+2118, are still possible.
197
198       Unicode also added some name abbreviations, which Perl now accepts: SP
199       for SPACE; TAB for CHARACTER TABULATION; NEW LINE, END OF LINE, NL, and
200       EOL for LINE FEED; LOCKING-SHIFT ONE for SHIFT OUT; LOCKING-SHIFT ZERO
201       for SHIFT IN; and ZWNBSP for ZERO WIDTH NO-BREAK SPACE.
202
203       More details on this version of Unicode are provided in
204       <http://www.unicode.org/versions/Unicode6.1.0/>.
205
206       "use charnames" is no longer needed for "\N{name}"
207
208       When "\N{name}" is encountered, the "charnames" module is now
209       automatically loaded when needed as if the ":full" and ":short" options
210       had been specified.  See charnames for more information.
211
212       "\N{...}" can now have Unicode loose name matching
213
214       This is described in the "charnames" item in "Updated Modules and
215       Pragmata" below.
216
217       Unicode Symbol Names
218
219       Perl now has proper support for Unicode in symbol names.  It used to be
220       that "*{$foo}" would ignore the internal UTF8 flag and use the bytes of
221       the underlying representation to look up the symbol.  That meant that
222       "*{"\x{100}"}" and "*{"\xc4\x80"}" would return the same thing.  All
223       these parts of Perl have been fixed to account for Unicode:
224
225       •   Method names (including those passed to "use overload")
226
227       •   Typeglob names (including names of variables, subroutines, and
228           filehandles)
229
230       •   Package names
231
232       •   "goto"
233
234       •   Symbolic dereferencing
235
236       •   Second argument to "bless()" and "tie()"
237
238       •   Return value of "ref()"
239
240       •   Subroutine prototypes
241
242       •   Attributes
243
244       •   Various warnings and error messages that mention variable names or
245           values, methods, etc.
246
247       In addition, a parsing bug has been fixed that prevented "*{e}" from
248       implicitly quoting the name, but instead interpreted it as "*{+e}",
249       which would cause a strict violation.
250
251       "*{"*a::b"}" automatically strips off the * if it is followed by an
252       ASCII letter.  That has been extended to all Unicode identifier
253       characters.
254
255       One-character non-ASCII non-punctuation variables (like "$e") are now
256       subject to "Used only once" warnings.  They used to be exempt, as they
257       were treated as punctuation variables.
258
259       Also, single-character Unicode punctuation variables (like $X) are now
260       supported [perl #69032].
261
262       Improved ability to mix locales and Unicode, including UTF-8 locales
263
264       An optional parameter has been added to "use locale"
265
266        use locale ':not_characters';
267
268       which tells Perl to use all but the "LC_CTYPE" and "LC_COLLATE"
269       portions of the current locale.  Instead, the character set is assumed
270       to be Unicode.  This lets locales and Unicode be seamlessly mixed,
271       including the increasingly frequent UTF-8 locales.  When using this
272       hybrid form of locales, the ":locale" layer to the open pragma can be
273       used to interface with the file system, and there are CPAN modules
274       available for ARGV and environment variable conversions.
275
276       Full details are in perllocale.
277
278       New function "fc" and corresponding escape sequence "\F" for Unicode
279       foldcase
280
281       Unicode foldcase is an extension to lowercase that gives better results
282       when comparing two strings case-insensitively.  It has long been used
283       internally in regular expression "/i" matching.  Now it is available
284       explicitly through the new "fc" function call (enabled by
285       "use feature 'fc'", or "use v5.16", or explicitly callable via
286       "CORE::fc") or through the new "\F" sequence in double-quotish strings.
287
288       Full details are in "fc" in perlfunc.
289
290       The Unicode "Script_Extensions" property is now supported.
291
292       New in Unicode 6.0, this is an improved "Script" property.  Details are
293       in "Scripts" in perlunicode.
294
295   XS Changes
296       Improved typemaps for Some Builtin Types
297
298       Most XS authors will know there is a longstanding bug in the OUTPUT
299       typemap for T_AVREF ("AV*"), T_HVREF ("HV*"), T_CVREF ("CV*"), and
300       T_SVREF ("SVREF" or "\$foo") that requires manually decrementing the
301       reference count of the return value instead of the typemap taking care
302       of this.  For backwards-compatibility, this cannot be changed in the
303       default typemaps.  But we now provide additional typemaps
304       "T_AVREF_REFCOUNT_FIXED", etc. that do not exhibit this bug.  Using
305       them in your extension is as simple as having one line in your
306       "TYPEMAP" section:
307
308         HV*   T_HVREF_REFCOUNT_FIXED
309
310       "is_utf8_char()"
311
312       The XS-callable function "is_utf8_char()", when presented with
313       malformed UTF-8 input, can read up to 12 bytes beyond the end of the
314       string.  This cannot be fixed without changing its API, and so its use
315       is now deprecated.  Use "is_utf8_char_buf()" (described just below)
316       instead.
317
318       Added "is_utf8_char_buf()"
319
320       This function is designed to replace the deprecated "is_utf8_char()"
321       function.  It includes an extra parameter to make sure it doesn't read
322       past the end of the input buffer.
323
324       Other "is_utf8_foo()" functions, as well as "utf8_to_foo()", etc.
325
326       Most other XS-callable functions that take UTF-8 encoded input
327       implicitly assume that the UTF-8 is valid (not malformed) with respect
328       to buffer length.  Do not do things such as change a character's case
329       or see if it is alphanumeric without first being sure that it is valid
330       UTF-8.  This can be safely done for a whole string by using one of the
331       functions "is_utf8_string()", "is_utf8_string_loc()", and
332       "is_utf8_string_loclen()".
333
334       New Pad API
335
336       Many new functions have been added to the API for manipulating lexical
337       pads.  See "Pad Data Structures" in perlapi for more information.
338
339   Changes to Special Variables
340       $$ can be assigned to
341
342       $$ was made read-only in Perl 5.8.0.  But only sometimes: "local $$"
343       would make it writable again.  Some CPAN modules were using "local $$"
344       or XS code to bypass the read-only check, so there is no reason to keep
345       $$ read-only.  (This change also allowed a bug to be fixed while
346       maintaining backward compatibility.)
347
348       $^X converted to an absolute path on FreeBSD, OS X and Solaris
349
350       $^X is now converted to an absolute path on OS X, FreeBSD (without
351       needing /proc mounted) and Solaris 10 and 11.  This augments the
352       previous approach of using /proc on Linux, FreeBSD, and NetBSD (in all
353       cases, where mounted).
354
355       This makes relocatable perl installations more useful on these
356       platforms.  (See "Relocatable @INC" in INSTALL)
357
358   Debugger Changes
359       Features inside the debugger
360
361       The current Perl's feature bundle is now enabled for commands entered
362       in the interactive debugger.
363
364       New option for the debugger's t command
365
366       The t command in the debugger, which toggles tracing mode, now accepts
367       a numeric argument that determines how many levels of subroutine calls
368       to trace.
369
370       "enable" and "disable"
371
372       The debugger now has "disable" and "enable" commands for disabling
373       existing breakpoints and re-enabling them.  See perldebug.
374
375       Breakpoints with file names
376
377       The debugger's "b" command for setting breakpoints now lets a line
378       number be prefixed with a file name.  See "b [file]:[line] [condition]"
379       in perldebug.
380
381   The "CORE" Namespace
382       The "CORE::" prefix
383
384       The "CORE::" prefix can now be used on keywords enabled by feature.pm,
385       even outside the scope of "use feature".
386
387       Subroutines in the "CORE" namespace
388
389       Many Perl keywords are now available as subroutines in the CORE
390       namespace.  This lets them be aliased:
391
392           BEGIN { *entangle = \&CORE::tie }
393           entangle $variable, $package, @args;
394
395       And for prototypes to be bypassed:
396
397           sub mytie(\[%$*@]$@) {
398               my ($ref, $pack, @args) = @_;
399               ... do something ...
400               goto &CORE::tie;
401           }
402
403       Some of these cannot be called through references or via &foo syntax,
404       but must be called as barewords.
405
406       See CORE for details.
407
408   Other Changes
409       Anonymous handles
410
411       Automatically generated file handles are now named __ANONIO__ when the
412       variable name cannot be determined, rather than $__ANONIO__.
413
414       Autoloaded sort Subroutines
415
416       Custom sort subroutines can now be autoloaded [perl #30661]:
417
418           sub AUTOLOAD { ... }
419           @sorted = sort foo @list; # uses AUTOLOAD
420
421       "continue" no longer requires the "switch" feature
422
423       The "continue" keyword has two meanings.  It can introduce a "continue"
424       block after a loop, or it can exit the current "when" block.  Up to
425       now, the latter meaning was valid only with the "switch" feature
426       enabled, and was a syntax error otherwise.  Since the main purpose of
427       feature.pm is to avoid conflicts with user-defined subroutines, there
428       is no reason for "continue" to depend on it.
429
430       DTrace probes for interpreter phase change
431
432       The "phase-change" probes will fire when the interpreter's phase
433       changes, which tracks the "${^GLOBAL_PHASE}" variable.  "arg0" is the
434       new phase name; "arg1" is the old one.  This is useful for limiting
435       your instrumentation to one or more of: compile time, run time, or
436       destruct time.
437
438       "__FILE__()" Syntax
439
440       The "__FILE__", "__LINE__" and "__PACKAGE__" tokens can now be written
441       with an empty pair of parentheses after them.  This makes them parse
442       the same way as "time", "fork" and other built-in functions.
443
444       The "\$" prototype accepts any scalar lvalue
445
446       The "\$" and "\[$]" subroutine prototypes now accept any scalar lvalue
447       argument.  Previously they accepted only scalars beginning with "$" and
448       hash and array elements.  This change makes them consistent with the
449       way the built-in "read" and "recv" functions (among others) parse their
450       arguments.  This means that one can override the built-in functions
451       with custom subroutines that parse their arguments the same way.
452
453       "_" in subroutine prototypes
454
455       The "_" character in subroutine prototypes is now allowed before "@" or
456       "%".
457

Security

459   Use "is_utf8_char_buf()" and not "is_utf8_char()"
460       The latter function is now deprecated because its API is insufficient
461       to guarantee that it doesn't read (up to 12 bytes in the worst case)
462       beyond the end of its input string.  See is_utf8_char_buf().
463
464   Malformed UTF-8 input could cause attempts to read beyond the end of the
465       buffer
466       Two new XS-accessible functions, "utf8_to_uvchr_buf()" and
467       "utf8_to_uvuni_buf()" are now available to prevent this, and the Perl
468       core has been converted to use them.  See "Internal Changes".
469
470   "File::Glob::bsd_glob()" memory error with GLOB_ALTDIRFUNC (CVE-2011-2728).
471       Calling "File::Glob::bsd_glob" with the unsupported flag
472       GLOB_ALTDIRFUNC would cause an access violation / segfault.  A Perl
473       program that accepts a flags value from an external source could expose
474       itself to denial of service or arbitrary code execution attacks.  There
475       are no known exploits in the wild.  The problem has been corrected by
476       explicitly disabling all unsupported flags and setting unused function
477       pointers to null.  Bug reported by Clement Lecigne. (5.14.2)
478
479   Privileges are now set correctly when assigning to $(
480       A hypothetical bug (probably unexploitable in practice) because the
481       incorrect setting of the effective group ID while setting $( has been
482       fixed.  The bug would have affected only systems that have
483       "setresgid()" but not "setregid()", but no such systems are known to
484       exist.
485

Deprecations

487   Don't read the Unicode data base files in lib/unicore
488       It is now deprecated to directly read the Unicode data base files.
489       These are stored in the lib/unicore directory.  Instead, you should use
490       the new functions in Unicode::UCD.  These provide a stable API, and
491       give complete information.
492
493       Perl may at some point in the future change or remove these files.  The
494       file which applications were most likely to have used is
495       lib/unicore/ToDigit.pl.  "prop_invmap()" in Unicode::UCD can be used to
496       get at its data instead.
497
498   XS functions "is_utf8_char()", "utf8_to_uvchr()" and "utf8_to_uvuni()"
499       This function is deprecated because it could read beyond the end of the
500       input string.  Use the new is_utf8_char_buf(), "utf8_to_uvchr_buf()"
501       and "utf8_to_uvuni_buf()" instead.
502

Future Deprecations

504       This section serves as a notice of features that are likely to be
505       removed or deprecated in the next release of perl (5.18.0).  If your
506       code depends on these features, you should contact the Perl 5 Porters
507       via the mailing list <http://lists.perl.org/list/perl5-porters.html> or
508       perlbug to explain your use case and inform the deprecation process.
509
510   Core Modules
511       These modules may be marked as deprecated from the core.  This only
512       means that they will no longer be installed by default with the core
513       distribution, but will remain available on the CPAN.
514
515       •   CPANPLUS
516
517       •   Filter::Simple
518
519       •   PerlIO::mmap
520
521       •   Pod::LaTeX
522
523       •   Pod::Parser
524
525       •   SelfLoader
526
527       •   Text::Soundex
528
529       •   Thread.pm
530
531   Platforms with no supporting programmers
532       These platforms will probably have their special build support removed
533       during the 5.17.0 development series.
534
535       •   BeOS
536
537       •   djgpp
538
539       •   dgux
540
541       •   EPOC
542
543       •   MPE/iX
544
545       •   Rhapsody
546
547       •   UTS
548
549       •   VM/ESA
550
551   Other Future Deprecations
552       •   Swapping of $< and $>
553
554           For more information about this future deprecation, see the
555           relevant RT ticket <https://github.com/Perl/perl5/issues/11547>.
556
557       •   sfio, stdio
558
559           Perl supports being built without PerlIO proper, using a stdio or
560           sfio wrapper instead.  A perl build like this will not support IO
561           layers and thus Unicode IO, making it rather handicapped.
562
563           PerlIO supports a "stdio" layer if stdio use is desired, and
564           similarly a sfio layer could be produced.
565
566       •   Unescaped literal "{" in regular expressions.
567
568           Starting with v5.20, it is planned to require a literal "{" to be
569           escaped, for example by preceding it with a backslash.  In v5.18, a
570           deprecated warning message will be emitted for all such uses.  This
571           affects only patterns that are to match a literal "{".  Other uses
572           of this character, such as part of a quantifier or sequence as in
573           those below, are completely unaffected:
574
575               /foo{3,5}/
576               /\p{Alphabetic}/
577               /\N{DIGIT ZERO}
578
579           Removing this will permit extensions to Perl's pattern syntax and
580           better error checking for existing syntax.  See "Quantifiers" in
581           perlre for an example.
582
583       •   Revamping "\Q" semantics in double-quotish strings when combined
584           with other escapes.
585
586           There are several bugs and inconsistencies involving combinations
587           of "\Q" and escapes like "\x", "\L", etc., within a "\Q...\E" pair.
588           These need to be fixed, and doing so will necessarily change
589           current behavior.  The changes have not yet been settled.
590

Incompatible Changes

592   Special blocks called in void context
593       Special blocks ("BEGIN", "CHECK", "INIT", "UNITCHECK", "END") are now
594       called in void context.  This avoids wasteful copying of the result of
595       the last statement [perl #108794].
596
597   The "overloading" pragma and regexp objects
598       With "no overloading", regular expression objects returned by "qr//"
599       are now stringified as "Regexp=REGEXP(0xbe600d)" instead of the regular
600       expression itself [perl #108780].
601
602   Two XS typemap Entries removed
603       Two presumably unused XS typemap entries have been removed from the
604       core typemap: T_DATAUNIT and T_CALLBACK.  If you are, against all odds,
605       a user of these, please see the instructions on how to restore them in
606       perlxstypemap.
607
608   Unicode 6.1 has incompatibilities with Unicode 6.0
609       These are detailed in "Supports (almost) Unicode 6.1" above.  You can
610       compile this version of Perl to use Unicode 6.0.  See "Hacking Perl to
611       work on earlier Unicode versions (for very serious hackers only)" in
612       perlunicode.
613
614   Borland compiler
615       All support for the Borland compiler has been dropped.  The code had
616       not worked for a long time anyway.
617
618   Certain deprecated Unicode properties are no longer supported by default
619       Perl should never have exposed certain Unicode properties that are used
620       by Unicode internally and not meant to be publicly available.  Use of
621       these has generated deprecated warning messages since Perl 5.12.  The
622       removed properties are Other_Alphabetic,
623       Other_Default_Ignorable_Code_Point, Other_Grapheme_Extend,
624       Other_ID_Continue, Other_ID_Start, Other_Lowercase, Other_Math, and
625       Other_Uppercase.
626
627       Perl may be recompiled to include any or all of them; instructions are
628       given in "Unicode character properties that are NOT accepted by Perl"
629       in perluniprops.
630
631   Dereferencing IO thingies as typeglobs
632       The "*{...}" operator, when passed a reference to an IO thingy (as in
633       "*{*STDIN{IO}}"), creates a new typeglob containing just that IO
634       object.  Previously, it would stringify as an empty string, but some
635       operators would treat it as undefined, producing an "uninitialized"
636       warning.  Now it stringifies as __ANONIO__ [perl #96326].
637
638   User-defined case-changing operations
639       This feature was deprecated in Perl 5.14, and has now been removed.
640       The CPAN module Unicode::Casing provides better functionality without
641       the drawbacks that this feature had, as are detailed in the 5.14
642       documentation:
643       <http://perldoc.perl.org/5.14.0/perlunicode.html#User-Defined-Case-Mappings-%28for-serious-hackers-only%29>
644
645   XSUBs are now 'static'
646       XSUB C functions are now 'static', that is, they are not visible from
647       outside the compilation unit.  Users can use the new
648       "XS_EXTERNAL(name)" and "XS_INTERNAL(name)" macros to pick the desired
649       linking behavior.  The ordinary "XS(name)" declaration for XSUBs will
650       continue to declare non-'static' XSUBs for compatibility, but the XS
651       compiler, ExtUtils::ParseXS ("xsubpp") will emit 'static' XSUBs by
652       default.  ExtUtils::ParseXS's behavior can be reconfigured from XS
653       using the "EXPORT_XSUB_SYMBOLS" keyword.  See perlxs for details.
654
655   Weakening read-only references
656       Weakening read-only references is no longer permitted.  It should never
657       have worked anyway, and could sometimes result in crashes.
658
659   Tying scalars that hold typeglobs
660       Attempting to tie a scalar after a typeglob was assigned to it would
661       instead tie the handle in the typeglob's IO slot.  This meant that it
662       was impossible to tie the scalar itself.  Similar problems affected
663       "tied" and "untie": "tied $scalar" would return false on a tied scalar
664       if the last thing returned was a typeglob, and "untie $scalar" on such
665       a tied scalar would do nothing.
666
667       We fixed this problem before Perl 5.14.0, but it caused problems with
668       some CPAN modules, so we put in a deprecation cycle instead.
669
670       Now the deprecation has been removed and this bug has been fixed.  So
671       "tie $scalar" will always tie the scalar, not the handle it holds.  To
672       tie the handle, use "tie *$scalar" (with an explicit asterisk).  The
673       same applies to "tied *$scalar" and "untie *$scalar".
674
675   IPC::Open3 no longer provides "xfork()", "xclose_on_exec()" and
676       "xpipe_anon()"
677       All three functions were private, undocumented, and unexported.  They
678       do not appear to be used by any code on CPAN.  Two have been inlined
679       and one deleted entirely.
680
681   $$ no longer caches PID
682       Previously, if one called fork(3) from C, Perl's notion of $$ could go
683       out of sync with what getpid() returns.  By always fetching the value
684       of $$ via getpid(), this potential bug is eliminated.  Code that
685       depends on the caching behavior will break.  As described in Core
686       Enhancements, $$ is now writable, but it will be reset during a fork.
687
688   $$ and "getppid()" no longer emulate POSIX semantics under LinuxThreads
689       The POSIX emulation of $$ and "getppid()" under the obsolete
690       LinuxThreads implementation has been removed.  This only impacts users
691       of Linux 2.4 and users of Debian GNU/kFreeBSD up to and including 6.0,
692       not the vast majority of Linux installations that use NPTL threads.
693
694       This means that "getppid()", like $$, is now always guaranteed to
695       return the OS's idea of the current state of the process, not perl's
696       cached version of it.
697
698       See the documentation for $$ for details.
699
700   $<, $>, $( and $) are no longer cached
701       Similarly to the changes to $$ and "getppid()", the internal caching of
702       $<, $>, $( and $) has been removed.
703
704       When we cached these values our idea of what they were would drift out
705       of sync with reality if someone (e.g., someone embedding perl) called
706       "sete?[ug]id()" without updating "PL_e?[ug]id".  Having to deal with
707       this complexity wasn't worth it given how cheap the "gete?[ug]id()"
708       system call is.
709
710       This change will break a handful of CPAN modules that use the XS-level
711       "PL_uid", "PL_gid", "PL_euid" or "PL_egid" variables.
712
713       The fix for those breakages is to use "PerlProc_gete?[ug]id()" to
714       retrieve them (e.g., "PerlProc_getuid()"), and not to assign to
715       "PL_e?[ug]id" if you change the UID/GID/EUID/EGID.  There is no longer
716       any need to do so since perl will always retrieve the up-to-date
717       version of those values from the OS.
718
719   Which Non-ASCII characters get quoted by "quotemeta" and "\Q" has changed
720       This is unlikely to result in a real problem, as Perl does not attach
721       special meaning to any non-ASCII character, so it is currently
722       irrelevant which are quoted or not.  This change fixes bug [perl
723       #77654] and brings Perl's behavior more into line with Unicode's
724       recommendations.  See "quotemeta" in perlfunc.
725

Performance Enhancements

727       •   Improved performance for Unicode properties in regular expressions
728
729           Matching a code point against a Unicode property is now done via a
730           binary search instead of linear.  This means for example that the
731           worst case for a 1000 item property is 10 probes instead of 1000.
732           This inefficiency has been compensated for in the past by
733           permanently storing in a hash the results of a given probe plus the
734           results for the adjacent 64 code points, under the theory that
735           near-by code points are likely to be searched for.  A separate hash
736           was used for each mention of a Unicode property in each regular
737           expression.  Thus, "qr/\p{foo}abc\p{foo}/" would generate two
738           hashes.  Any probes in one instance would be unknown to the other,
739           and the hashes could expand separately to be quite large if the
740           regular expression were used on many different widely-separated
741           code points.  Now, however, there is just one hash shared by all
742           instances of a given property.  This means that if "\p{foo}" is
743           matched against "A" in one regular expression in a thread, the
744           result will be known immediately to all regular expressions, and
745           the relentless march of using up memory is slowed considerably.
746
747       •   Version declarations with the "use" keyword (e.g., "use 5.012") are
748           now faster, as they enable features without loading feature.pm.
749
750       •   "local $_" is faster now, as it no longer iterates through magic
751           that it is not going to copy anyway.
752
753       •   Perl 5.12.0 sped up the destruction of objects whose classes define
754           empty "DESTROY" methods (to prevent autoloading), by simply not
755           calling such empty methods.  This release takes this optimization a
756           step further, by not calling any "DESTROY" method that begins with
757           a "return" statement.  This can be useful for destructors that are
758           only used for debugging:
759
760               use constant DEBUG => 1;
761               sub DESTROY { return unless DEBUG; ... }
762
763           Constant-folding will reduce the first statement to "return;" if
764           DEBUG is set to 0, triggering this optimization.
765
766       •   Assigning to a variable that holds a typeglob or copy-on-write
767           scalar is now much faster.  Previously the typeglob would be
768           stringified or the copy-on-write scalar would be copied before
769           being clobbered.
770
771       •   Assignment to "substr" in void context is now more than twice its
772           previous speed.  Instead of creating and returning a special lvalue
773           scalar that is then assigned to, "substr" modifies the original
774           string itself.
775
776       •   "substr" no longer calculates a value to return when called in void
777           context.
778
779       •   Due to changes in File::Glob, Perl's "glob" function and its
780           "<...>" equivalent are now much faster.  The splitting of the
781           pattern into words has been rewritten in C, resulting in speed-ups
782           of 20% for some cases.
783
784           This does not affect "glob" on VMS, as it does not use File::Glob.
785
786       •   The short-circuiting operators "&&", "||", and "//", when chained
787           (such as "$a || $b || $c"), are now considerably faster to short-
788           circuit, due to reduced optree traversal.
789
790       •   The implementation of "s///r" makes one fewer copy of the scalar's
791           value.
792
793       •   Recursive calls to lvalue subroutines in lvalue scalar context use
794           less memory.
795

Modules and Pragmata

797   Deprecated Modules
798       Version::Requirements
799           Version::Requirements is now DEPRECATED, use
800           CPAN::Meta::Requirements, which is a drop-in replacement.  It will
801           be deleted from perl.git blead in v5.17.0.
802
803   New Modules and Pragmata
804       •   arybase -- this new module implements the $[ variable.
805
806       •   PerlIO::mmap 0.010 has been added to the Perl core.
807
808           The "mmap" PerlIO layer is no longer implemented by perl itself,
809           but has been moved out into the new PerlIO::mmap module.
810
811   Updated Modules and Pragmata
812       This is only an overview of selected module updates.  For a complete
813       list of updates, run:
814
815           $ corelist --diff 5.14.0 5.16.0
816
817       You can substitute your favorite version in place of 5.14.0, too.
818
819       •   Archive::Extract has been upgraded from version 0.48 to 0.58.
820
821           Includes a fix for FreeBSD to only use "unzip" if it is located in
822           "/usr/local/bin", as FreeBSD 9.0 will ship with a limited "unzip"
823           in "/usr/bin".
824
825       •   Archive::Tar has been upgraded from version 1.76 to 1.82.
826
827           Adjustments to handle files >8gb (>0777777777777 octal) and a
828           feature to return the MD5SUM of files in the archive.
829
830       •   base has been upgraded from version 2.16 to 2.18.
831
832           "base" no longer sets a module's $VERSION to "-1" when a module it
833           loads does not define a $VERSION.  This change has been made
834           because "-1" is not a valid version number under the new "lax"
835           criteria used internally by "UNIVERSAL::VERSION".  (See version for
836           more on "lax" version criteria.)
837
838           "base" no longer internally skips loading modules it has already
839           loaded and instead relies on "require" to inspect %INC.  This fixes
840           a bug when "base" is used with code that clear %INC to force a
841           module to be reloaded.
842
843       •   Carp has been upgraded from version 1.20 to 1.26.
844
845           It now includes last read filehandle info and puts a dot after the
846           file and line number, just like errors from "die" [perl #106538].
847
848       •   charnames has been updated from version 1.18 to 1.30.
849
850           "charnames" can now be invoked with a new option, ":loose", which
851           is like the existing ":full" option, but enables Unicode loose name
852           matching.  Details are in "LOOSE MATCHES" in charnames.
853
854       •   B::Deparse has been upgraded from version 1.03 to 1.14.  This fixes
855           numerous deparsing bugs.
856
857       •   CGI has been upgraded from version 3.52 to 3.59.
858
859           It uses the public and documented FCGI.pm API in CGI::Fast.
860           CGI::Fast was using an FCGI API that was deprecated and removed
861           from documentation more than ten years ago.  Usage of this
862           deprecated API with FCGI >= 0.70 or FCGI <= 0.73 introduces a
863           security issue.
864           <https://rt.cpan.org/Public/Bug/Display.html?id=68380>
865           <http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2011-2766>
866
867           Things that may break your code:
868
869           "url()" was fixed to return "PATH_INFO" when it is explicitly
870           requested with either the "path=>1" or "path_info=>1" flag.
871
872           If your code is running under mod_rewrite (or compatible) and you
873           are calling "self_url()" or you are calling "url()" and passing
874           "path_info=>1", these methods will actually be returning
875           "PATH_INFO" now, as you have explicitly requested or "self_url()"
876           has requested on your behalf.
877
878           The "PATH_INFO" has been omitted in such URLs since the issue was
879           introduced in the 3.12 release in December, 2005.
880
881           This bug is so old your application may have come to depend on it
882           or workaround it. Check for application before upgrading to this
883           release.
884
885           Examples of affected method calls:
886
887             $q->url(-absolute => 1, -query => 1, -path_info => 1);
888             $q->url(-path=>1);
889             $q->url(-full=>1,-path=>1);
890             $q->url(-rewrite=>1,-path=>1);
891             $q->self_url();
892
893           We no longer read from STDIN when the Content-Length is not set,
894           preventing requests with no Content-Length from sometimes freezing.
895           This is consistent with the CGI RFC 3875, and is also consistent
896           with CGI::Simple.  However, the old behavior may have been expected
897           by some command-line uses of CGI.pm.
898
899           In addition, the DELETE HTTP verb is now supported.
900
901       •   Compress::Zlib has been upgraded from version 2.035 to 2.048.
902
903           IO::Compress::Zip and IO::Uncompress::Unzip now have support for
904           LZMA (method 14).  There is a fix for a CRC issue in
905           IO::Compress::Unzip and it supports Streamed Stored context now.
906           And fixed a Zip64 issue in IO::Compress::Zip when the content size
907           was exactly 0xFFFFFFFF.
908
909       •   Digest::SHA has been upgraded from version 5.61 to 5.71.
910
911           Added BITS mode to the addfile method and shasum.  This makes
912           partial-byte inputs possible via files/STDIN and lets shasum check
913           all 8074 NIST Msg vectors, where previously special programming was
914           required to do this.
915
916       •   Encode has been upgraded from version 2.42 to 2.44.
917
918           Missing aliases added, a deep recursion error fixed and various
919           documentation updates.
920
921           Addressed 'decode_xs n-byte heap-overflow' security bug in
922           Unicode.xs (CVE-2011-2939). (5.14.2)
923
924       •   ExtUtils::CBuilder updated from version 0.280203 to 0.280206.
925
926           The new version appends CFLAGS and LDFLAGS to their Config.pm
927           counterparts.
928
929       •   ExtUtils::ParseXS has been upgraded from version 2.2210 to 3.16.
930
931           Much of ExtUtils::ParseXS, the module behind the XS compiler
932           "xsubpp", was rewritten and cleaned up.  It has been made somewhat
933           more extensible and now finally uses strictures.
934
935           The typemap logic has been moved into a separate module,
936           ExtUtils::Typemaps.  See "New Modules and Pragmata", above.
937
938           For a complete set of changes, please see the ExtUtils::ParseXS
939           changelog, available on the CPAN.
940
941       •   File::Glob has been upgraded from version 1.12 to 1.17.
942
943           On Windows, tilde (~) expansion now checks the "USERPROFILE"
944           environment variable, after checking "HOME".
945
946           It has a new ":bsd_glob" export tag, intended to replace ":glob".
947           Like ":glob" it overrides "glob" with a function that does not
948           split the glob pattern into words, but, unlike ":glob", it iterates
949           properly in scalar context, instead of returning the last file.
950
951           There are other changes affecting Perl's own "glob" operator (which
952           uses File::Glob internally, except on VMS).  See "Performance
953           Enhancements" and "Selected Bug Fixes".
954
955       •   FindBin updated from version 1.50 to 1.51.
956
957           It no longer returns a wrong result if a script of the same name as
958           the current one exists in the path and is executable.
959
960       •   HTTP::Tiny has been upgraded from version 0.012 to 0.017.
961
962           Added support for using $ENV{http_proxy} to set the default proxy
963           host.
964
965           Adds additional shorthand methods for all common HTTP verbs, a
966           "post_form()" method for POST-ing x-www-form-urlencoded data and a
967           "www_form_urlencode()" utility method.
968
969       •   IO has been upgraded from version 1.25_04 to 1.25_06, and
970           IO::Handle from version 1.31 to 1.33.
971
972           Together, these upgrades fix a problem with IO::Handle's "getline"
973           and "getlines" methods.  When these methods are called on the
974           special ARGV handle, the next file is automatically opened, as
975           happens with the built-in "<>" and "readline" functions.  But,
976           unlike the built-ins, these methods were not respecting the
977           caller's use of the open pragma and applying the appropriate I/O
978           layers to the newly-opened file [rt.cpan.org #66474].
979
980       •   IPC::Cmd has been upgraded from version 0.70 to 0.76.
981
982           Capturing of command output (both "STDOUT" and "STDERR") is now
983           supported using IPC::Open3 on MSWin32 without requiring IPC::Run.
984
985       •   IPC::Open3 has been upgraded from version 1.09 to 1.12.
986
987           Fixes a bug which prevented use of "open3" on Windows when *STDIN,
988           *STDOUT or *STDERR had been localized.
989
990           Fixes a bug which prevented duplicating numeric file descriptors on
991           Windows.
992
993           "open3" with "-" for the program name works once more.  This was
994           broken in version 1.06 (and hence in Perl 5.14.0) [perl #95748].
995
996       •   Locale::Codes has been upgraded from version 3.16 to 3.21.
997
998           Added Language Extension codes (langext) and Language Variation
999           codes (langvar) as defined in the IANA language registry.
1000
1001           Added language codes from ISO 639-5
1002
1003           Added language/script codes from the IANA language subtag registry
1004
1005           Fixed an uninitialized value warning [rt.cpan.org #67438].
1006
1007           Fixed the return value for the all_XXX_codes and all_XXX_names
1008           functions [rt.cpan.org #69100].
1009
1010           Reorganized modules to move Locale::MODULE to Locale::Codes::MODULE
1011           to allow for cleaner future additions.  The original four modules
1012           (Locale::Language, Locale::Currency, Locale::Country,
1013           Locale::Script) will continue to work, but all new sets of codes
1014           will be added in the Locale::Codes namespace.
1015
1016           The code2XXX, XXX2code, all_XXX_codes, and all_XXX_names functions
1017           now support retired codes.  All codesets may be specified by a
1018           constant or by their name now.  Previously, they were specified
1019           only by a constant.
1020
1021           The alias_code function exists for backward compatibility.  It has
1022           been replaced by rename_country_code.  The alias_code function will
1023           be removed some time after September, 2013.
1024
1025           All work is now done in the central module (Locale::Codes).
1026           Previously, some was still done in the wrapper modules
1027           (Locale::Codes::*).  Added Language Family codes (langfam) as
1028           defined in ISO 639-5.
1029
1030       •   Math::BigFloat has been upgraded from version 1.993 to 1.997.
1031
1032           The "numify" method has been corrected to return a normalized Perl
1033           number (the result of "0 + $thing"), instead of a string
1034           [rt.cpan.org #66732].
1035
1036       •   Math::BigInt has been upgraded from version 1.994 to 1.998.
1037
1038           It provides a new "bsgn" method that complements the "babs" method.
1039
1040           It fixes the internal "objectify" function's handling of "foreign
1041           objects" so they are converted to the appropriate class
1042           (Math::BigInt or Math::BigFloat).
1043
1044       •   Math::BigRat has been upgraded from version 0.2602 to 0.2603.
1045
1046           "int()" on a Math::BigRat object containing -1/2 now creates a
1047           Math::BigInt containing 0, rather than -0.  Math::BigInt does not
1048           even support negative zero, so the resulting object was actually
1049           malformed [perl #95530].
1050
1051       •   Math::Complex has been upgraded from version 1.56 to 1.59 and
1052           Math::Trig from version 1.2 to 1.22.
1053
1054           Fixes include: correct copy constructor usage; fix polarwise
1055           formatting with numeric format specifier; and more stable
1056           "great_circle_direction" algorithm.
1057
1058       •   Module::CoreList has been upgraded from version 2.51 to 2.66.
1059
1060           The "corelist" utility now understands the "-r" option for
1061           displaying Perl release dates and the "--diff" option to print the
1062           set of modlib changes between two perl distributions.
1063
1064       •   Module::Metadata has been upgraded from version 1.000004 to
1065           1.000009.
1066
1067           Adds "provides" method to generate a CPAN META provides data
1068           structure correctly; use of "package_versions_from_directory" is
1069           discouraged.
1070
1071       •   ODBM_File has been upgraded from version 1.10 to 1.12.
1072
1073           The XS code is now compiled with "PERL_NO_GET_CONTEXT", which will
1074           aid performance under ithreads.
1075
1076       •   open has been upgraded from version 1.08 to 1.10.
1077
1078           It no longer turns off layers on standard handles when invoked
1079           without the ":std" directive.  Similarly, when invoked with the
1080           ":std" directive, it now clears layers on STDERR before applying
1081           the new ones, and not just on STDIN and STDOUT [perl #92728].
1082
1083       •   overload has been upgraded from version 1.13 to 1.18.
1084
1085           "overload::Overloaded" no longer calls "can" on the class, but uses
1086           another means to determine whether the object has overloading.  It
1087           was never correct for it to call "can", as overloading does not
1088           respect AUTOLOAD.  So classes that autoload methods and implement
1089           "can" no longer have to account for overloading [perl #40333].
1090
1091           A warning is now produced for invalid arguments.  See "New
1092           Diagnostics".
1093
1094       •   PerlIO::scalar has been upgraded from version 0.11 to 0.14.
1095
1096           (This is the module that implements "open $fh, '>', \$scalar".)
1097
1098           It fixes a problem with "open my $fh, ">", \$scalar" not working if
1099           $scalar is a copy-on-write scalar. (5.14.2)
1100
1101           It also fixes a hang that occurs with "readline" or "<$fh>" if a
1102           typeglob has been assigned to $scalar [perl #92258].
1103
1104           It no longer assumes during "seek" that $scalar is a string
1105           internally.  If it didn't crash, it was close to doing so [perl
1106           #92706].  Also, the internal print routine no longer assumes that
1107           the position set by "seek" is valid, but extends the string to that
1108           position, filling the intervening bytes (between the old length and
1109           the seek position) with nulls [perl #78980].
1110
1111           Printing to an in-memory handle now works if the $scalar holds a
1112           reference, stringifying the reference before modifying it.
1113           References used to be treated as empty strings.
1114
1115           Printing to an in-memory handle no longer crashes if the $scalar
1116           happens to hold a number internally, but no string buffer.
1117
1118           Printing to an in-memory handle no longer creates scalars that
1119           confuse the regular expression engine [perl #108398].
1120
1121       •   Pod::Functions has been upgraded from version 1.04 to 1.05.
1122
1123           Functions.pm is now generated at perl build time from annotations
1124           in perlfunc.pod.  This will ensure that Pod::Functions and perlfunc
1125           remain in synchronisation.
1126
1127       •   Pod::Html has been upgraded from version 1.11 to 1.1502.
1128
1129           This is an extensive rewrite of Pod::Html to use Pod::Simple under
1130           the hood.  The output has changed significantly.
1131
1132       •   Pod::Perldoc has been upgraded from version 3.15_03 to 3.17.
1133
1134           It corrects the search paths on VMS [perl #90640]. (5.14.1)
1135
1136           The -v option now fetches the right section for $0.
1137
1138           This upgrade has numerous significant fixes.  Consult its changelog
1139           on the CPAN for more information.
1140
1141       •   POSIX has been upgraded from version 1.24 to 1.30.
1142
1143           POSIX no longer uses AutoLoader.  Any code which was relying on
1144           this implementation detail was buggy, and may fail because of this
1145           change.  The module's Perl code has been considerably simplified,
1146           roughly halving the number of lines, with no change in
1147           functionality.  The XS code has been refactored to reduce the size
1148           of the shared object by about 12%, with no change in functionality.
1149           More POSIX functions now have tests.
1150
1151           "sigsuspend" and "pause" now run signal handlers before returning,
1152           as the whole point of these two functions is to wait until a signal
1153           has arrived, and then return after it has been triggered.  Delayed,
1154           or "safe", signals were preventing that from happening, possibly
1155           resulting in race conditions [perl #107216].
1156
1157           "POSIX::sleep" is now a direct call into the underlying OS "sleep"
1158           function, instead of being a Perl wrapper on "CORE::sleep".
1159           "POSIX::dup2" now returns the correct value on Win32 (i.e., the
1160           file descriptor).  "POSIX::SigSet" "sigsuspend" and "sigpending"
1161           and "POSIX::pause" now dispatch safe signals immediately before
1162           returning to their caller.
1163
1164           "POSIX::Termios::setattr" now defaults the third argument to
1165           "TCSANOW", instead of 0. On most platforms "TCSANOW" is defined to
1166           be 0, but on some 0 is not a valid parameter, which caused a call
1167           with defaults to fail.
1168
1169       •   Socket has been upgraded from version 1.94 to 2.001.
1170
1171           It has new functions and constants for handling IPv6 sockets:
1172
1173               pack_ipv6_mreq
1174               unpack_ipv6_mreq
1175               IPV6_ADD_MEMBERSHIP
1176               IPV6_DROP_MEMBERSHIP
1177               IPV6_MTU
1178               IPV6_MTU_DISCOVER
1179               IPV6_MULTICAST_HOPS
1180               IPV6_MULTICAST_IF
1181               IPV6_MULTICAST_LOOP
1182               IPV6_UNICAST_HOPS
1183               IPV6_V6ONLY
1184
1185       •   Storable has been upgraded from version 2.27 to 2.34.
1186
1187           It no longer turns copy-on-write scalars into read-only scalars
1188           when freezing and thawing.
1189
1190       •   Sys::Syslog has been upgraded from version 0.27 to 0.29.
1191
1192           This upgrade closes many outstanding bugs.
1193
1194       •   Term::ANSIColor has been upgraded from version 3.00 to 3.01.
1195
1196           Only interpret an initial array reference as a list of colors, not
1197           any initial reference, allowing the colored function to work
1198           properly on objects with stringification defined.
1199
1200       •   Term::ReadLine has been upgraded from version 1.07 to 1.09.
1201
1202           Term::ReadLine now supports any event loop, including unpublished
1203           ones and simple IO::Select, loops without the need to rewrite
1204           existing code for any particular framework [perl #108470].
1205
1206       •   threads::shared has been upgraded from version 1.37 to 1.40.
1207
1208           Destructors on shared objects used to be ignored sometimes if the
1209           objects were referenced only by shared data structures.  This has
1210           been mostly fixed, but destructors may still be ignored if the
1211           objects still exist at global destruction time [perl #98204].
1212
1213       •   Unicode::Collate has been upgraded from version 0.73 to 0.89.
1214
1215           Updated to CLDR 1.9.1
1216
1217           Locales updated to CLDR 2.0: mk, mt, nb, nn, ro, ru, sk, sr, sv,
1218           uk, zh__pinyin, zh__stroke
1219
1220           Newly supported locales: bn, fa, ml, mr, or, pa, sa, si,
1221           si__dictionary, sr_Latn, sv__reformed, ta, te, th, ur, wae.
1222
1223           Tailored compatibility ideographs as well as unified ideographs for
1224           the locales: ja, ko, zh__big5han, zh__gb2312han, zh__pinyin,
1225           zh__stroke.
1226
1227           Locale/*.pl files are now searched for in @INC.
1228
1229       •   Unicode::Normalize has been upgraded from version 1.10 to 1.14.
1230
1231           Fixes for the removal of unicore/CompositionExclusions.txt from
1232           core.
1233
1234       •   Unicode::UCD has been upgraded from version 0.32 to 0.43.
1235
1236           This adds four new functions:  "prop_aliases()" and
1237           "prop_value_aliases()", which are used to find all Unicode-approved
1238           synonyms for property names, or to convert from one name to
1239           another; "prop_invlist" which returns all code points matching a
1240           given Unicode binary property; and "prop_invmap" which returns the
1241           complete specification of a given Unicode property.
1242
1243       •   Win32API::File has been upgraded from version 0.1101 to 0.1200.
1244
1245           Added SetStdHandle and GetStdHandle functions
1246
1247   Removed Modules and Pragmata
1248       As promised in Perl 5.14.0's release notes, the following modules have
1249       been removed from the core distribution, and if needed should be
1250       installed from CPAN instead.
1251
1252       •   Devel::DProf has been removed from the Perl core.  Prior version
1253           was 20110228.00.
1254
1255       •   Shell has been removed from the Perl core.  Prior version was
1256           0.72_01.
1257
1258       •   Several old perl4-style libraries which have been deprecated with
1259           5.14 are now removed:
1260
1261               abbrev.pl assert.pl bigfloat.pl bigint.pl bigrat.pl cacheout.pl
1262               complete.pl ctime.pl dotsh.pl exceptions.pl fastcwd.pl flush.pl
1263               getcwd.pl getopt.pl getopts.pl hostname.pl importenv.pl
1264               lib/find{,depth}.pl look.pl newgetopt.pl open2.pl open3.pl
1265               pwd.pl shellwords.pl stat.pl tainted.pl termcap.pl timelocal.pl
1266
1267           They can be found on CPAN as Perl4::CoreLibs.
1268

Documentation

1270   New Documentation
1271       perldtrace
1272
1273       perldtrace describes Perl's DTrace support, listing the provided probes
1274       and gives examples of their use.
1275
1276       perlexperiment
1277
1278       This document is intended to provide a list of experimental features in
1279       Perl.  It is still a work in progress.
1280
1281       perlootut
1282
1283       This a new OO tutorial.  It focuses on basic OO concepts, and then
1284       recommends that readers choose an OO framework from CPAN.
1285
1286       perlxstypemap
1287
1288       The new manual describes the XS typemapping mechanism in unprecedented
1289       detail and combines new documentation with information extracted from
1290       perlxs and the previously unofficial list of all core typemaps.
1291
1292   Changes to Existing Documentation
1293       perlapi
1294
1295       •   The HV API has long accepted negative lengths to show that the key
1296           is in UTF8.  This is now documented.
1297
1298       •   The "boolSV()" macro is now documented.
1299
1300       perlfunc
1301
1302       •   "dbmopen" treats a 0 mode as a special case, that prevents a
1303           nonexistent file from being created.  This has been the case since
1304           Perl 5.000, but was never documented anywhere.  Now the perlfunc
1305           entry mentions it [perl #90064].
1306
1307       •   As an accident of history, "open $fh, '<:', ..." applies the
1308           default layers for the platform (":raw" on Unix, ":crlf" on
1309           Windows), ignoring whatever is declared by open.pm.  This seems
1310           such a useful feature it has been documented in perlfunc and open.
1311
1312       •   The entry for "split" has been rewritten.  It is now far clearer
1313           than before.
1314
1315       perlguts
1316
1317       •   A new section, Autoloading with XSUBs, has been added, which
1318           explains the two APIs for accessing the name of the autoloaded sub.
1319
1320       •   Some function descriptions in perlguts were confusing, as it was
1321           not clear whether they referred to the function above or below the
1322           description.  This has been clarified [perl #91790].
1323
1324       perlobj
1325
1326       •   This document has been rewritten from scratch, and its coverage of
1327           various OO concepts has been expanded.
1328
1329       perlop
1330
1331       •   Documentation of the smartmatch operator has been reworked and
1332           moved from perlsyn to perlop where it belongs.
1333
1334           It has also been corrected for the case of "undef" on the left-hand
1335           side.  The list of different smart match behaviors had an item in
1336           the wrong place.
1337
1338       •   Documentation of the ellipsis statement ("...") has been reworked
1339           and moved from perlop to perlsyn.
1340
1341       •   The explanation of bitwise operators has been expanded to explain
1342           how they work on Unicode strings (5.14.1).
1343
1344       •   More examples for "m//g" have been added (5.14.1).
1345
1346       •   The "<<\FOO" here-doc syntax has been documented (5.14.1).
1347
1348       perlpragma
1349
1350       •   There is now a standard convention for naming keys in the "%^H",
1351           documented under Key naming.
1352
1353       "Laundering and Detecting Tainted Data" in perlsec
1354
1355       •   The example function for checking for taintedness contained a
1356           subtle error.  $@ needs to be localized to prevent its changing
1357           this global's value outside the function.  The preferred method to
1358           check for this remains "tainted" in Scalar::Util.
1359
1360       perllol
1361
1362       •   perllol has been expanded with examples using the new "push
1363           $scalar" syntax introduced in Perl 5.14.0 (5.14.1).
1364
1365       perlmod
1366
1367       •   perlmod now states explicitly that some types of explicit symbol
1368           table manipulation are not supported.  This codifies what was
1369           effectively already the case [perl #78074].
1370
1371       perlpodstyle
1372
1373       •   The tips on which formatting codes to use have been corrected and
1374           greatly expanded.
1375
1376       •   There are now a couple of example one-liners for previewing POD
1377           files after they have been edited.
1378
1379       perlre
1380
1381       •   The "(*COMMIT)" directive is now listed in the right section (Verbs
1382           without an argument).
1383
1384       perlrun
1385
1386       •   perlrun has undergone a significant clean-up.  Most notably, the
1387           -0x... form of the -0 flag has been clarified, and the final
1388           section on environment variables has been corrected and expanded
1389           (5.14.1).
1390
1391       perlsub
1392
1393       •   The ($;) prototype syntax, which has existed for rather a long
1394           time, is now documented in perlsub.  It lets a unary function have
1395           the same precedence as a list operator.
1396
1397       perltie
1398
1399       •   The required syntax for tying handles has been documented.
1400
1401       perlvar
1402
1403       •   The documentation for $! has been corrected and clarified.  It used
1404           to state that $! could be "undef", which is not the case.  It was
1405           also unclear whether system calls set C's "errno" or Perl's $!
1406           [perl #91614].
1407
1408       •   Documentation for $$ has been amended with additional cautions
1409           regarding changing the process ID.
1410
1411       Other Changes
1412
1413       •   perlxs was extended with documentation on inline typemaps.
1414
1415       •   perlref has a new Circular References section explaining how
1416           circularities may not be freed and how to solve that with weak
1417           references.
1418
1419       •   Parts of perlapi were clarified, and Perl equivalents of some C
1420           functions have been added as an additional mode of exposition.
1421
1422       •   A few parts of perlre and perlrecharclass were clarified.
1423
1424   Removed Documentation
1425       Old OO Documentation
1426
1427       The old OO tutorials, perltoot, perltooc, and perlboot, have been
1428       removed.  The perlbot (bag of object tricks) document has been removed
1429       as well.
1430
1431       Development Deltas
1432
1433       The perldelta files for development releases are no longer packaged
1434       with perl.  These can still be found in the perl source code
1435       repository.
1436

Diagnostics

1438       The following additions or changes have been made to diagnostic output,
1439       including warnings and fatal error messages.  For the complete list of
1440       diagnostic messages, see perldiag.
1441
1442   New Diagnostics
1443       New Errors
1444
1445       •   Cannot set tied @DB::args
1446
1447           This error occurs when "caller" tries to set @DB::args but finds it
1448           tied.  Before this error was added, it used to crash instead.
1449
1450       •   Cannot tie unreifiable array
1451
1452           This error is part of a safety check that the "tie" operator does
1453           before tying a special array like @_.  You should never see this
1454           message.
1455
1456       •   &CORE::%s cannot be called directly
1457
1458           This occurs when a subroutine in the "CORE::" namespace is called
1459           with &foo syntax or through a reference.  Some subroutines in this
1460           package cannot yet be called that way, but must be called as
1461           barewords.  See "Subroutines in the "CORE" namespace", above.
1462
1463       •   Source filters apply only to byte streams
1464
1465           This new error occurs when you try to activate a source filter
1466           (usually by loading a source filter module) within a string passed
1467           to "eval" under the "unicode_eval" feature.
1468
1469       New Warnings
1470
1471       •   defined(@array) is deprecated
1472
1473           The long-deprecated "defined(@array)" now also warns for package
1474           variables.  Previously it issued a warning for lexical variables
1475           only.
1476
1477length() used on %s
1478
1479           This new warning occurs when "length" is used on an array or hash,
1480           instead of "scalar(@array)" or "scalar(keys %hash)".
1481
1482       •   lvalue attribute %s already-defined subroutine
1483
1484           attributes.pm now emits this warning when the :lvalue attribute is
1485           applied to a Perl subroutine that has already been defined, as
1486           doing so can have unexpected side-effects.
1487
1488       •   overload arg '%s' is invalid
1489
1490           This warning, in the "overload" category, is produced when the
1491           overload pragma is given an argument it doesn't recognize,
1492           presumably a mistyped operator.
1493
1494       •   $[ used in %s (did you mean $] ?)
1495
1496           This new warning exists to catch the mistaken use of $[ in version
1497           checks.  $], not $[, contains the version number.
1498
1499       •   Useless assignment to a temporary
1500
1501           Assigning to a temporary scalar returned from an lvalue subroutine
1502           now produces this warning [perl #31946].
1503
1504       •   Useless use of \E
1505
1506           "\E" does nothing unless preceded by "\Q", "\L" or "\U".
1507
1508   Removed Errors
1509       •   "sort is now a reserved word"
1510
1511           This error used to occur when "sort" was called without arguments,
1512           followed by ";" or ")".  (E.g., "sort;" would die, but "{sort}" was
1513           OK.)  This error message was added in Perl 3 to catch code like
1514           "close(sort)" which would no longer work.  More than two decades
1515           later, this message is no longer appropriate.  Now "sort" without
1516           arguments is always allowed, and returns an empty list, as it did
1517           in those cases where it was already allowed [perl #90030].
1518
1519   Changes to Existing Diagnostics
1520       •   The "Applying pattern match..." or similar warning produced when an
1521           array or hash is on the left-hand side of the "=~" operator now
1522           mentions the name of the variable.
1523
1524       •   The "Attempt to free non-existent shared string" has had the
1525           spelling of "non-existent" corrected to "nonexistent".  It was
1526           already listed with the correct spelling in perldiag.
1527
1528       •   The error messages for using "default" and "when" outside a
1529           topicalizer have been standardized to match the messages for
1530           "continue" and loop controls.  They now read 'Can't "default"
1531           outside a topicalizer' and 'Can't "when" outside a topicalizer'.
1532           They both used to be 'Can't use when() outside a topicalizer' [perl
1533           #91514].
1534
1535       •   The message, "Code point 0x%X is not Unicode, no properties match
1536           it; all inverse properties do" has been changed to "Code point 0x%X
1537           is not Unicode, all \p{} matches fail; all \P{} matches succeed".
1538
1539       •   Redefinition warnings for constant subroutines used to be
1540           mandatory, even occurring under "no warnings".  Now they respect
1541           the warnings pragma.
1542
1543       •   The "glob failed" warning message is now suppressible via "no
1544           warnings" [perl #111656].
1545
1546       •   The Invalid version format error message now says "negative version
1547           number" within the parentheses, rather than "non-numeric data", for
1548           negative numbers.
1549
1550       •   The two warnings Possible attempt to put comments in qw() list and
1551           Possible attempt to separate words with commas are no longer
1552           mutually exclusive: the same "qw" construct may produce both.
1553
1554       •   The uninitialized warning for "y///r" when $_ is implicit and
1555           undefined now mentions the variable name, just like the non-/r
1556           variation of the operator.
1557
1558       •   The 'Use of "foo" without parentheses is ambiguous' warning has
1559           been extended to apply also to user-defined subroutines with a (;$)
1560           prototype, and not just to built-in functions.
1561
1562       •   Warnings that mention the names of lexical ("my") variables with
1563           Unicode characters in them now respect the presence or absence of
1564           the ":utf8" layer on the output handle, instead of outputting UTF8
1565           regardless.  Also, the correct names are included in the strings
1566           passed to $SIG{__WARN__} handlers, rather than the raw UTF8 bytes.
1567

Utility Changes

1569       h2ph
1570
1571       •   h2ph used to generate code of the form
1572
1573             unless(defined(&FOO)) {
1574               sub FOO () {42;}
1575             }
1576
1577           But the subroutine is a compile-time declaration, and is hence
1578           unaffected by the condition.  It has now been corrected to emit a
1579           string "eval" around the subroutine [perl #99368].
1580
1581       splain
1582
1583splain no longer emits backtraces with the first line number
1584           repeated.
1585
1586           This:
1587
1588               Uncaught exception from user code:
1589                       Cannot fwiddle the fwuddle at -e line 1.
1590                at -e line 1
1591                       main::baz() called at -e line 1
1592                       main::bar() called at -e line 1
1593                       main::foo() called at -e line 1
1594
1595           has become this:
1596
1597               Uncaught exception from user code:
1598                       Cannot fwiddle the fwuddle at -e line 1.
1599                       main::baz() called at -e line 1
1600                       main::bar() called at -e line 1
1601                       main::foo() called at -e line 1
1602
1603       •   Some error messages consist of multiple lines that are listed as
1604           separate entries in perldiag.  splain has been taught to find the
1605           separate entries in these cases, instead of simply failing to find
1606           the message.
1607
1608       zipdetails
1609
1610       •   This is a new utility, included as part of an IO::Compress::Base
1611           upgrade.
1612
1613           zipdetails displays information about the internal record structure
1614           of the zip file.  It is not concerned with displaying any details
1615           of the compressed data stored in the zip file.
1616

Configuration and Compilation

1618regexp.h has been modified for compatibility with GCC's -Werror
1619           option, as used by some projects that include perl's header files
1620           (5.14.1).
1621
1622       •   "USE_LOCALE{,_COLLATE,_CTYPE,_NUMERIC}" have been added the output
1623           of perl -V as they have affect the behavior of the interpreter
1624           binary (albeit in only a small area).
1625
1626       •   The code and tests for IPC::Open2 have been moved from
1627           ext/IPC-Open2 into ext/IPC-Open3, as "IPC::Open2::open2()" is
1628           implemented as a thin wrapper around "IPC::Open3::_open3()", and
1629           hence is very tightly coupled to it.
1630
1631       •   The magic types and magic vtables are now generated from data in a
1632           new script regen/mg_vtable.pl, instead of being maintained by hand.
1633           As different EBCDIC variants can't agree on the code point for '~',
1634           the character to code point conversion is done at build time by
1635           generate_uudmap to a new generated header mg_data.h.  "PL_vtbl_bm"
1636           and "PL_vtbl_fm" are now defined by the pre-processor as
1637           "PL_vtbl_regexp", instead of being distinct C variables.
1638           "PL_vtbl_sig" has been removed.
1639
1640       •   Building with "-DPERL_GLOBAL_STRUCT" works again.  This
1641           configuration is not generally used.
1642
1643       •   Perl configured with MAD now correctly frees "MADPROP" structures
1644           when OPs are freed.  "MADPROP"s are now allocated with
1645           "PerlMemShared_malloc()"
1646
1647makedef.pl has been refactored.  This should have no noticeable
1648           affect on any of the platforms that use it as part of their build
1649           (AIX, VMS, Win32).
1650
1651       •   "useperlio" can no longer be disabled.
1652
1653       •   The file global.sym is no longer needed, and has been removed.  It
1654           contained a list of all exported functions, one of the files
1655           generated by regen/embed.pl from data in embed.fnc and
1656           regen/opcodes.  The code has been refactored so that the only user
1657           of global.sym, makedef.pl, now reads embed.fnc and regen/opcodes
1658           directly, removing the need to store the list of exported functions
1659           in an intermediate file.
1660
1661           As global.sym was never installed, this change should not be
1662           visible outside the build process.
1663
1664pod/buildtoc, used by the build process to build perltoc, has been
1665           refactored and simplified.  It now contains only code to build
1666           perltoc; the code to regenerate Makefiles has been moved to
1667           Porting/pod_rules.pl.  It's a bug if this change has any material
1668           effect on the build process.
1669
1670pod/roffitall is now built by pod/buildtoc, instead of being
1671           shipped with the distribution.  Its list of manpages is now
1672           generated (and therefore current).  See also RT #103202 for an
1673           unresolved related issue.
1674
1675       •   The man page for "XS::Typemap" is no longer installed.
1676           "XS::Typemap" is a test module which is not installed, hence
1677           installing its documentation makes no sense.
1678
1679       •   The -Dusesitecustomize and -Duserelocatableinc options now work
1680           together properly.
1681

Platform Support

1683   Platform-Specific Notes
1684       Cygwin
1685
1686       •   Since version 1.7, Cygwin supports native UTF-8 paths.  If Perl is
1687           built under that environment, directory and filenames will be UTF-8
1688           encoded.
1689
1690       •   Cygwin does not initialize all original Win32 environment
1691           variables.  See README.cygwin for a discussion of the newly-added
1692           "Cygwin::sync_winenv()" function [perl #110190] and for further
1693           links.
1694
1695       HP-UX
1696
1697       •   HP-UX PA-RISC/64 now supports gcc-4.x
1698
1699           A fix to correct the socketsize now makes the test suite pass on
1700           HP-UX PA-RISC for 64bitall builds. (5.14.2)
1701
1702       VMS
1703
1704       •   Remove unnecessary includes, fix miscellaneous compiler warnings
1705           and close some unclosed comments on vms/vms.c.
1706
1707       •   Remove sockadapt layer from the VMS build.
1708
1709       •   Explicit support for VMS versions before v7.0 and DEC C versions
1710           before v6.0 has been removed.
1711
1712       •   Since Perl 5.10.1, the home-grown "stat" wrapper has been unable to
1713           distinguish between a directory name containing an underscore and
1714           an otherwise-identical filename containing a dot in the same
1715           position (e.g., t/test_pl as a directory and t/test.pl as a file).
1716           This problem has been corrected.
1717
1718       •   The build on VMS now permits names of the resulting symbols in C
1719           code for Perl longer than 31 characters.  Symbols like
1720           "Perl__it_was_the_best_of_times_it_was_the_worst_of_times" can now
1721           be created freely without causing the VMS linker to seize up.
1722
1723       GNU/Hurd
1724
1725       •   Numerous build and test failures on GNU/Hurd have been resolved
1726           with hints for building DBM modules, detection of the library
1727           search path, and enabling of large file support.
1728
1729       OpenVOS
1730
1731       •   Perl is now built with dynamic linking on OpenVOS, the minimum
1732           supported version of which is now Release 17.1.0.
1733
1734       SunOS
1735
1736       The CC workshop C++ compiler is now detected and used on systems that
1737       ship without cc.
1738

Internal Changes

1740       •   The compiled representation of formats is now stored via the
1741           "mg_ptr" of their "PERL_MAGIC_fm".  Previously it was stored in the
1742           string buffer, beyond "SvLEN()", the regular end of the string.
1743           "SvCOMPILED()" and "SvCOMPILED_{on,off}()" now exist solely for
1744           compatibility for XS code.  The first is always 0, the other two
1745           now no-ops. (5.14.1)
1746
1747       •   Some global variables have been marked "const", members in the
1748           interpreter structure have been re-ordered, and the opcodes have
1749           been re-ordered.  The op "OP_AELEMFAST" has been split into
1750           "OP_AELEMFAST" and "OP_AELEMFAST_LEX".
1751
1752       •   When empting a hash of its elements (e.g., via undef(%h), or
1753           %h=()), HvARRAY field is no longer temporarily zeroed.  Any
1754           destructors called on the freed elements see the remaining
1755           elements.  Thus, %h=() becomes more like "delete $h{$_} for keys
1756           %h".
1757
1758       •   Boyer-Moore compiled scalars are now PVMGs, and the Boyer-Moore
1759           tables are now stored via the mg_ptr of their "PERL_MAGIC_bm".
1760           Previously they were PVGVs, with the tables stored in the string
1761           buffer, beyond "SvLEN()".  This eliminates the last place where the
1762           core stores data beyond "SvLEN()".
1763
1764       •   Simplified logic in "Perl_sv_magic()" introduces a small change of
1765           behavior for error cases involving unknown magic types.
1766           Previously, if "Perl_sv_magic()" was passed a magic type unknown to
1767           it, it would
1768
1769           1.  Croak "Modification of a read-only value attempted" if read
1770               only
1771
1772           2.  Return without error if the SV happened to already have this
1773               magic
1774
1775           3.  otherwise croak "Don't know how to handle magic of type \\%o"
1776
1777           Now it will always croak "Don't know how to handle magic of type
1778           \\%o", even on read-only values, or SVs which already have the
1779           unknown magic type.
1780
1781       •   The experimental "fetch_cop_label" function has been renamed to
1782           "cop_fetch_label".
1783
1784       •   The "cop_store_label" function has been added to the API, but is
1785           experimental.
1786
1787embedvar.h has been simplified, and one level of macro indirection
1788           for PL_* variables has been removed for the default (non-
1789           multiplicity) configuration.  PERLVAR*() macros now directly expand
1790           their arguments to tokens such as "PL_defgv", instead of expanding
1791           to "PL_Idefgv", with embedvar.h defining a macro to map "PL_Idefgv"
1792           to "PL_defgv".  XS code which has unwarranted chumminess with the
1793           implementation may need updating.
1794
1795       •   An API has been added to explicitly choose whether to export XSUB
1796           symbols.  More detail can be found in the comments for commit
1797           e64345f8.
1798
1799       •   The "is_gv_magical_sv" function has been eliminated and merged with
1800           "gv_fetchpvn_flags".  It used to be called to determine whether a
1801           GV should be autovivified in rvalue context.  Now it has been
1802           replaced with a new "GV_ADDMG" flag (not part of the API).
1803
1804       •   The returned code point from the function "utf8n_to_uvuni()" when
1805           the input is malformed UTF-8, malformations are allowed, and "utf8"
1806           warnings are off is now the Unicode REPLACEMENT CHARACTER whenever
1807           the malformation is such that no well-defined code point can be
1808           computed.  Previously the returned value was essentially garbage.
1809           The only malformations that have well-defined values are a zero-
1810           length string (0 is the return), and overlong UTF-8 sequences.
1811
1812       •   Padlists are now marked "AvREAL"; i.e., reference-counted.  They
1813           have always been reference-counted, but were not marked real,
1814           because pad.c did its own clean-up, instead of using the usual
1815           clean-up code in sv.c.  That caused problems in thread cloning, so
1816           now the "AvREAL" flag is on, but is turned off in pad.c right
1817           before the padlist is freed (after pad.c has done its custom
1818           freeing of the pads).
1819
1820       •   All C files that make up the Perl core have been converted to
1821           UTF-8.
1822
1823       •   These new functions have been added as part of the work on Unicode
1824           symbols:
1825
1826               HvNAMELEN
1827               HvNAMEUTF8
1828               HvENAMELEN
1829               HvENAMEUTF8
1830               gv_init_pv
1831               gv_init_pvn
1832               gv_init_pvsv
1833               gv_fetchmeth_pv
1834               gv_fetchmeth_pvn
1835               gv_fetchmeth_sv
1836               gv_fetchmeth_pv_autoload
1837               gv_fetchmeth_pvn_autoload
1838               gv_fetchmeth_sv_autoload
1839               gv_fetchmethod_pv_flags
1840               gv_fetchmethod_pvn_flags
1841               gv_fetchmethod_sv_flags
1842               gv_autoload_pv
1843               gv_autoload_pvn
1844               gv_autoload_sv
1845               newGVgen_flags
1846               sv_derived_from_pv
1847               sv_derived_from_pvn
1848               sv_derived_from_sv
1849               sv_does_pv
1850               sv_does_pvn
1851               sv_does_sv
1852               whichsig_pv
1853               whichsig_pvn
1854               whichsig_sv
1855               newCONSTSUB_flags
1856
1857           The gv_fetchmethod_*_flags functions, like gv_fetchmethod_flags,
1858           are experimental and may change in a future release.
1859
1860       •   The following functions were added.  These are not part of the API:
1861
1862               GvNAMEUTF8
1863               GvENAMELEN
1864               GvENAME_HEK
1865               CopSTASH_flags
1866               CopSTASH_flags_set
1867               PmopSTASH_flags
1868               PmopSTASH_flags_set
1869               sv_sethek
1870               HEKfARG
1871
1872           There is also a "HEKf" macro corresponding to "SVf", for
1873           interpolating HEKs in formatted strings.
1874
1875       •   "sv_catpvn_flags" takes a couple of new internal-only flags,
1876           "SV_CATBYTES" and "SV_CATUTF8", which tell it whether the char
1877           array to be concatenated is UTF8.  This allows for more efficient
1878           concatenation than creating temporary SVs to pass to "sv_catsv".
1879
1880       •   For XS AUTOLOAD subs, $AUTOLOAD is set once more, as it was in
1881           5.6.0.  This is in addition to setting "SvPVX(cv)", for
1882           compatibility with 5.8 to 5.14.  See "Autoloading with XSUBs" in
1883           perlguts.
1884
1885       •   Perl now checks whether the array (the linearized isa) returned by
1886           a MRO plugin begins with the name of the class itself, for which
1887           the array was created, instead of assuming that it does.  This
1888           prevents the first element from being skipped during method lookup.
1889           It also means that "mro::get_linear_isa" may return an array with
1890           one more element than the MRO plugin provided [perl #94306].
1891
1892       •   "PL_curstash" is now reference-counted.
1893
1894       •   There are now feature bundle hints in "PL_hints" ($^H) that version
1895           declarations use, to avoid having to load feature.pm.  One setting
1896           of the hint bits indicates a "custom" feature bundle, which means
1897           that the entries in "%^H" still apply.  feature.pm uses that.
1898
1899           The "HINT_FEATURE_MASK" macro is defined in perl.h along with other
1900           hints.  Other macros for setting and testing features and bundles
1901           are in the new feature.h.  "FEATURE_IS_ENABLED" (which has moved to
1902           feature.h) is no longer used throughout the codebase, but more
1903           specific macros, e.g., "FEATURE_SAY_IS_ENABLED", that are defined
1904           in feature.h.
1905
1906lib/feature.pm is now a generated file, created by the new
1907           regen/feature.pl script, which also generates feature.h.
1908
1909       •   Tied arrays are now always "AvREAL".  If @_ or "DB::args" is tied,
1910           it is reified first, to make sure this is always the case.
1911
1912       •   Two new functions "utf8_to_uvchr_buf()" and "utf8_to_uvuni_buf()"
1913           have been added.  These are the same as "utf8_to_uvchr" and
1914           "utf8_to_uvuni" (which are now deprecated), but take an extra
1915           parameter that is used to guard against reading beyond the end of
1916           the input string.  See "utf8_to_uvchr_buf" in perlapi and
1917           "utf8_to_uvuni_buf" in perlapi.
1918
1919       •   The regular expression engine now does TRIE case insensitive
1920           matches under Unicode. This may change the output of "use re
1921           'debug';", and will speed up various things.
1922
1923       •   There is a new "wrap_op_checker()" function, which provides a
1924           thread-safe alternative to writing to "PL_check" directly.
1925

Selected Bug Fixes

1927   Array and hash
1928       •   A bug has been fixed that would cause a "Use of freed value in
1929           iteration" error if the next two hash elements that would be
1930           iterated over are deleted [perl #85026]. (5.14.1)
1931
1932       •   Deleting the current hash iterator (the hash element that would be
1933           returned by the next call to "each") in void context used not to
1934           free it [perl #85026].
1935
1936       •   Deletion of methods via "delete $Class::{method}" syntax used to
1937           update method caches if called in void context, but not scalar or
1938           list context.
1939
1940       •   When hash elements are deleted in void context, the internal hash
1941           entry is now freed before the value is freed, to prevent
1942           destructors called by that latter freeing from seeing the hash in
1943           an inconsistent state.  It was possible to cause double-frees if
1944           the destructor freed the hash itself [perl #100340].
1945
1946       •   A "keys" optimization in Perl 5.12.0 to make it faster on empty
1947           hashes caused "each" not to reset the iterator if called after the
1948           last element was deleted.
1949
1950       •   Freeing deeply nested hashes no longer crashes [perl #44225].
1951
1952       •   It is possible from XS code to create hashes with elements that
1953           have no values.  The hash element and slice operators used to crash
1954           when handling these in lvalue context.  They now produce a
1955           "Modification of non-creatable hash value attempted" error message.
1956
1957       •   If list assignment to a hash or array triggered destructors that
1958           freed the hash or array itself, a crash would ensue.  This is no
1959           longer the case [perl #107440].
1960
1961       •   It used to be possible to free the typeglob of a localized array or
1962           hash (e.g., "local @{"x"}; delete $::{x}"), resulting in a crash on
1963           scope exit.
1964
1965       •   Some core bugs affecting Hash::Util have been fixed: locking a hash
1966           element that is a glob copy no longer causes the next assignment to
1967           it to corrupt the glob (5.14.2), and unlocking a hash element that
1968           holds a copy-on-write scalar no longer causes modifications to that
1969           scalar to modify other scalars that were sharing the same string
1970           buffer.
1971
1972   C API fixes
1973       •   The "newHVhv" XS function now works on tied hashes, instead of
1974           crashing or returning an empty hash.
1975
1976       •   The "SvIsCOW" C macro now returns false for read-only copies of
1977           typeglobs, such as those created by:
1978
1979             $hash{elem} = *foo;
1980             Hash::Util::lock_value %hash, 'elem';
1981
1982           It used to return true.
1983
1984       •   The "SvPVutf8" C function no longer tries to modify its argument,
1985           resulting in errors [perl #108994].
1986
1987       •   "SvPVutf8" now works properly with magical variables.
1988
1989       •   "SvPVbyte" now works properly non-PVs.
1990
1991       •   When presented with malformed UTF-8 input, the XS-callable
1992           functions "is_utf8_string()", "is_utf8_string_loc()", and
1993           "is_utf8_string_loclen()" could read beyond the end of the input
1994           string by up to 12 bytes.  This no longer happens.  [perl #32080].
1995           However, currently, "is_utf8_char()" still has this defect, see
1996           "is_utf8_char()" above.
1997
1998       •   The C-level "pregcomp" function could become confused about whether
1999           the pattern was in UTF8 if the pattern was an overloaded, tied, or
2000           otherwise magical scalar [perl #101940].
2001
2002   Compile-time hints
2003       •   Tying "%^H" no longer causes perl to crash or ignore the contents
2004           of "%^H" when entering a compilation scope [perl #106282].
2005
2006       •   "eval $string" and "require" used not to localize "%^H" during
2007           compilation if it was empty at the time the "eval" call itself was
2008           compiled.  This could lead to scary side effects, like "use re
2009           "/m"" enabling other flags that the surrounding code was trying to
2010           enable for its caller [perl #68750].
2011
2012       •   "eval $string" and "require" no longer localize hints ($^H and
2013           "%^H") at run time, but only during compilation of the $string or
2014           required file.  This makes "BEGIN { $^H{foo}=7 }" equivalent to
2015           "BEGIN { eval '$^H{foo}=7' }" [perl #70151].
2016
2017       •   Creating a BEGIN block from XS code (via "newXS" or "newATTRSUB")
2018           would, on completion, make the hints of the current compiling code
2019           the current hints.  This could cause warnings to occur in a non-
2020           warning scope.
2021
2022   Copy-on-write scalars
2023       Copy-on-write or shared hash key scalars were introduced in 5.8.0, but
2024       most Perl code did not encounter them (they were used mostly
2025       internally).  Perl 5.10.0 extended them, such that assigning
2026       "__PACKAGE__" or a hash key to a scalar would make it copy-on-write.
2027       Several parts of Perl were not updated to account for them, but have
2028       now been fixed.
2029
2030       •   "utf8::decode" had a nasty bug that would modify copy-on-write
2031           scalars' string buffers in place (i.e., skipping the copy).  This
2032           could result in hashes having two elements with the same key [perl
2033           #91834]. (5.14.2)
2034
2035       •   Lvalue subroutines were not allowing COW scalars to be returned.
2036           This was fixed for lvalue scalar context in Perl 5.12.3 and 5.14.0,
2037           but list context was not fixed until this release.
2038
2039       •   Elements of restricted hashes (see the fields pragma) containing
2040           copy-on-write values couldn't be deleted, nor could such hashes be
2041           cleared ("%hash = ()"). (5.14.2)
2042
2043       •   Localizing a tied variable used to make it read-only if it
2044           contained a copy-on-write string. (5.14.2)
2045
2046       •   Assigning a copy-on-write string to a stash element no longer
2047           causes a double free.  Regardless of this change, the results of
2048           such assignments are still undefined.
2049
2050       •   Assigning a copy-on-write string to a tied variable no longer stops
2051           that variable from being tied if it happens to be a PVMG or PVLV
2052           internally.
2053
2054       •   Doing a substitution on a tied variable returning a copy-on-write
2055           scalar used to cause an assertion failure or an "Attempt to free
2056           nonexistent shared string" warning.
2057
2058       •   This one is a regression from 5.12: In 5.14.0, the bitwise
2059           assignment operators "|=", "^=" and "&=" started leaving the left-
2060           hand side undefined if it happened to be a copy-on-write string
2061           [perl #108480].
2062
2063       •   Storable, Devel::Peek and PerlIO::scalar had similar problems.  See
2064           "Updated Modules and Pragmata", above.
2065
2066   The debugger
2067dumpvar.pl, and therefore the "x" command in the debugger, have
2068           been fixed to handle objects blessed into classes whose names
2069           contain "=".  The contents of such objects used not to be dumped
2070           [perl #101814].
2071
2072       •   The "R" command for restarting a debugger session has been fixed to
2073           work on Windows, or any other system lacking a
2074           "POSIX::_SC_OPEN_MAX" constant [perl #87740].
2075
2076       •   The "#line 42 foo" directive used not to update the arrays of lines
2077           used by the debugger if it occurred in a string eval.  This was
2078           partially fixed in 5.14, but it worked only for a single "#line 42
2079           foo" in each eval.  Now it works for multiple.
2080
2081       •   When subroutine calls are intercepted by the debugger, the name of
2082           the subroutine or a reference to it is stored in $DB::sub, for the
2083           debugger to access.  Sometimes (such as "$foo = *bar; undef *bar;
2084           &$foo") $DB::sub would be set to a name that could not be used to
2085           find the subroutine, and so the debugger's attempt to call it would
2086           fail.  Now the check to see whether a reference is needed is more
2087           robust, so those problems should not happen anymore [rt.cpan.org
2088           #69862].
2089
2090       •   Every subroutine has a filename associated with it that the
2091           debugger uses.  The one associated with constant subroutines used
2092           to be misallocated when cloned under threads.  Consequently,
2093           debugging threaded applications could result in memory corruption
2094           [perl #96126].
2095
2096   Dereferencing operators
2097       •   "defined(${"..."})", "defined(*{"..."})", etc., used to return true
2098           for most, but not all built-in variables, if they had not been used
2099           yet.  This bug affected "${^GLOBAL_PHASE}" and "${^UTF8CACHE}",
2100           among others.  It also used to return false if the package name was
2101           given as well ("${"::!"}") [perl #97978, #97492].
2102
2103       •   Perl 5.10.0 introduced a similar bug: "defined(*{"foo"})" where
2104           "foo" represents the name of a built-in global variable used to
2105           return false if the variable had never been used before, but only
2106           on the first call.  This, too, has been fixed.
2107
2108       •   Since 5.6.0, "*{ ... }" has been inconsistent in how it treats
2109           undefined values.  It would die in strict mode or lvalue context
2110           for most undefined values, but would be treated as the empty string
2111           (with a warning) for the specific scalar return by "undef()"
2112           (&PL_sv_undef internally).  This has been corrected.  "undef()" is
2113           now treated like other undefined scalars, as in Perl 5.005.
2114
2115   Filehandle, last-accessed
2116       Perl has an internal variable that stores the last filehandle to be
2117       accessed.  It is used by $. and by "tell" and "eof" without arguments.
2118
2119       •   It used to be possible to set this internal variable to a glob copy
2120           and then modify that glob copy to be something other than a glob,
2121           and still have the last-accessed filehandle associated with the
2122           variable after assigning a glob to it again:
2123
2124               my $foo = *STDOUT;  # $foo is a glob copy
2125               <$foo>;             # $foo is now the last-accessed handle
2126               $foo = 3;           # no longer a glob
2127               $foo = *STDERR;     # still the last-accessed handle
2128
2129           Now the "$foo = 3" assignment unsets that internal variable, so
2130           there is no last-accessed filehandle, just as if "<$foo>" had never
2131           happened.
2132
2133           This also prevents some unrelated handle from becoming the last-
2134           accessed handle if $foo falls out of scope and the same internal SV
2135           gets used for another handle [perl #97988].
2136
2137       •   A regression in 5.14 caused these statements not to set that
2138           internal variable:
2139
2140               my $fh = *STDOUT;
2141               tell $fh;
2142               eof  $fh;
2143               seek $fh, 0,0;
2144               tell     *$fh;
2145               eof      *$fh;
2146               seek     *$fh, 0,0;
2147               readline *$fh;
2148
2149           This is now fixed, but "tell *{ *$fh }" still has the problem, and
2150           it is not clear how to fix it [perl #106536].
2151
2152   Filetests and "stat"
2153       The term "filetests" refers to the operators that consist of a hyphen
2154       followed by a single letter: "-r", "-x", "-M", etc.  The term "stacked"
2155       when applied to filetests means followed by another filetest operator
2156       sharing the same operand, as in "-r -x -w $fooo".
2157
2158       •   "stat" produces more consistent warnings.  It no longer warns for
2159           "_" [perl #71002] and no longer skips the warning at times for
2160           other unopened handles.  It no longer warns about an unopened
2161           handle when the operating system's "fstat" function fails.
2162
2163       •   "stat" would sometimes return negative numbers for large inode
2164           numbers, because it was using the wrong internal C type. [perl
2165           #84590]
2166
2167       •   "lstat" is documented to fall back to "stat" (with a warning) when
2168           given a filehandle.  When passed an IO reference, it was actually
2169           doing the equivalent of "stat _" and ignoring the handle.
2170
2171       •   "-T _" with no preceding "stat" used to produce a confusing
2172           "uninitialized" warning, even though there is no visible
2173           uninitialized value to speak of.
2174
2175       •   "-T", "-B", "-l" and "-t" now work when stacked with other filetest
2176           operators [perl #77388].
2177
2178       •   In 5.14.0, filetest ops ("-r", "-x", etc.) started calling FETCH on
2179           a tied argument belonging to the previous argument to a list
2180           operator, if called with a bareword argument or no argument at all.
2181           This has been fixed, so "push @foo, $tied, -r" no longer calls
2182           FETCH on $tied.
2183
2184       •   In Perl 5.6, "-l" followed by anything other than a bareword would
2185           treat its argument as a file name.  That was changed in 5.8 for
2186           glob references ("\*foo"), but not for globs themselves (*foo).
2187           "-l" started returning "undef" for glob references without setting
2188           the last stat buffer that the "_" handle uses, but only if warnings
2189           were turned on.  With warnings off, it was the same as 5.6.  In
2190           other words, it was simply buggy and inconsistent.  Now the 5.6
2191           behavior has been restored.
2192
2193       •   "-l" followed by a bareword no longer "eats" the previous argument
2194           to the list operator in whose argument list it resides.  Hence,
2195           "print "bar", -l foo" now actually prints "bar", because "-l" on
2196           longer eats it.
2197
2198       •   Perl keeps several internal variables to keep track of the last
2199           stat buffer, from which file(handle) it originated, what type it
2200           was, and whether the last stat succeeded.
2201
2202           There were various cases where these could get out of synch,
2203           resulting in inconsistent or erratic behavior in edge cases (every
2204           mention of "-T" applies to "-B" as well):
2205
2206           •   "-T HANDLE", even though it does a "stat", was not resetting
2207               the last stat type, so an "lstat _" following it would merrily
2208               return the wrong results.  Also, it was not setting the success
2209               status.
2210
2211           •   Freeing the handle last used by "stat" or a filetest could
2212               result in "-T _" using an unrelated handle.
2213
2214           •   "stat" with an IO reference would not reset the stat type or
2215               record the filehandle for "-T _" to use.
2216
2217           •   Fatal warnings could cause the stat buffer not to be reset for
2218               a filetest operator on an unopened filehandle or "-l" on any
2219               handle.  Fatal warnings also stopped "-T" from setting $!.
2220
2221           •   When the last stat was on an unreadable file, "-T _" is
2222               supposed to return "undef", leaving the last stat buffer
2223               unchanged.  But it was setting the stat type, causing "lstat _"
2224               to stop working.
2225
2226           •   "-T FILENAME" was not resetting the internal stat buffers for
2227               unreadable files.
2228
2229           These have all been fixed.
2230
2231   Formats
2232       •   Several edge cases have been fixed with formats and "formline"; in
2233           particular, where the format itself is potentially variable (such
2234           as with ties and overloading), and where the format and data differ
2235           in their encoding.  In both these cases, it used to possible for
2236           the output to be corrupted [perl #91032].
2237
2238       •   "formline" no longer converts its argument into a string in-place.
2239           So passing a reference to "formline" no longer destroys the
2240           reference [perl #79532].
2241
2242       •   Assignment to $^A (the format output accumulator) now recalculates
2243           the number of lines output.
2244
2245   "given" and "when"
2246       •   "given" was not scoping its implicit $_ properly, resulting in
2247           memory leaks or "Variable is not available" warnings [perl #94682].
2248
2249       •   "given" was not calling set-magic on the implicit lexical $_ that
2250           it uses.  This meant, for example, that "pos" would be remembered
2251           from one execution of the same "given" block to the next, even if
2252           the input were a different variable [perl #84526].
2253
2254       •   "when" blocks are now capable of returning variables declared
2255           inside the enclosing "given" block [perl #93548].
2256
2257   The "glob" operator
2258       •   On OSes other than VMS, Perl's "glob" operator (and the "<...>"
2259           form) use File::Glob underneath.  File::Glob splits the pattern
2260           into words, before feeding each word to its "bsd_glob" function.
2261
2262           There were several inconsistencies in the way the split was done.
2263           Now quotation marks (' and ") are always treated as shell-style
2264           word delimiters (that allow whitespace as part of a word) and
2265           backslashes are always preserved, unless they exist to escape
2266           quotation marks.  Before, those would only sometimes be the case,
2267           depending on whether the pattern contained whitespace.  Also,
2268           escaped whitespace at the end of the pattern is no longer stripped
2269           [perl #40470].
2270
2271       •   "CORE::glob" now works as a way to call the default globbing
2272           function.  It used to respect overrides, despite the "CORE::"
2273           prefix.
2274
2275       •   Under miniperl (used to configure modules when perl itself is
2276           built), "glob" now clears %ENV before calling csh, since the latter
2277           croaks on some systems if it does not like the contents of the
2278           LS_COLORS environment variable [perl #98662].
2279
2280   Lvalue subroutines
2281       •   Explicit return now returns the actual argument passed to return,
2282           instead of copying it [perl #72724, #72706].
2283
2284       •   Lvalue subroutines used to enforce lvalue syntax (i.e., whatever
2285           can go on the left-hand side of "=") for the last statement and the
2286           arguments to return.  Since lvalue subroutines are not always
2287           called in lvalue context, this restriction has been lifted.
2288
2289       •   Lvalue subroutines are less restrictive about what values can be
2290           returned.  It used to croak on values returned by "shift" and
2291           "delete" and from other subroutines, but no longer does so [perl
2292           #71172].
2293
2294       •   Empty lvalue subroutines ("sub :lvalue {}") used to return @_ in
2295           list context.  All subroutines used to do this, but regular subs
2296           were fixed in Perl 5.8.2.  Now lvalue subroutines have been
2297           likewise fixed.
2298
2299       •   Autovivification now works on values returned from lvalue
2300           subroutines [perl #7946], as does returning "keys" in lvalue
2301           context.
2302
2303       •   Lvalue subroutines used to copy their return values in rvalue
2304           context.  Not only was this a waste of CPU cycles, but it also
2305           caused bugs.  A "($)" prototype would cause an lvalue sub to copy
2306           its return value [perl #51408], and "while(lvalue_sub() =~ m/.../g)
2307           { ... }" would loop endlessly [perl #78680].
2308
2309       •   When called in potential lvalue context (e.g., subroutine arguments
2310           or a list passed to "for"), lvalue subroutines used to copy any
2311           read-only value that was returned.  E.g., " sub :lvalue { $] } "
2312           would not return $], but a copy of it.
2313
2314       •   When called in potential lvalue context, an lvalue subroutine
2315           returning arrays or hashes used to bind the arrays or hashes to
2316           scalar variables, resulting in bugs.  This was fixed in 5.14.0 if
2317           an array were the first thing returned from the subroutine (but not
2318           for "$scalar, @array" or hashes being returned).  Now a more
2319           general fix has been applied [perl #23790].
2320
2321       •   Method calls whose arguments were all surrounded with "my()" or
2322           "our()" (as in "$object->method(my($a,$b))") used to force lvalue
2323           context on the subroutine.  This would prevent lvalue methods from
2324           returning certain values.
2325
2326       •   Lvalue sub calls that are not determined to be such at compile time
2327           (&$name or &{"name"}) are no longer exempt from strict refs if they
2328           occur in the last statement of an lvalue subroutine [perl #102486].
2329
2330       •   Sub calls whose subs are not visible at compile time, if they
2331           occurred in the last statement of an lvalue subroutine, would
2332           reject non-lvalue subroutines and die with "Can't modify non-lvalue
2333           subroutine call" [perl #102486].
2334
2335           Non-lvalue sub calls whose subs are visible at compile time
2336           exhibited the opposite bug.  If the call occurred in the last
2337           statement of an lvalue subroutine, there would be no error when the
2338           lvalue sub was called in lvalue context.  Perl would blindly assign
2339           to the temporary value returned by the non-lvalue subroutine.
2340
2341       •   "AUTOLOAD" routines used to take precedence over the actual sub
2342           being called (i.e., when autoloading wasn't needed), for sub calls
2343           in lvalue or potential lvalue context, if the subroutine was not
2344           visible at compile time.
2345
2346       •   Applying the ":lvalue" attribute to an XSUB or to an aliased
2347           subroutine stub with "sub foo :lvalue;" syntax stopped working in
2348           Perl 5.12.  This has been fixed.
2349
2350       •   Applying the :lvalue attribute to subroutine that is already
2351           defined does not work properly, as the attribute changes the way
2352           the sub is compiled.  Hence, Perl 5.12 began warning when an
2353           attempt is made to apply the attribute to an already defined sub.
2354           In such cases, the attribute is discarded.
2355
2356           But the change in 5.12 missed the case where custom attributes are
2357           also present: that case still silently and ineffectively applied
2358           the attribute.  That omission has now been corrected.  "sub foo
2359           :lvalue :Whatever" (when "foo" is already defined) now warns about
2360           the :lvalue attribute, and does not apply it.
2361
2362       •   A bug affecting lvalue context propagation through nested lvalue
2363           subroutine calls has been fixed.  Previously, returning a value in
2364           nested rvalue context would be treated as lvalue context by the
2365           inner subroutine call, resulting in some values (such as read-only
2366           values) being rejected.
2367
2368   Overloading
2369       •   Arithmetic assignment ("$left += $right") involving overloaded
2370           objects that rely on the 'nomethod' override no longer segfault
2371           when the left operand is not overloaded.
2372
2373       •   Errors that occur when methods cannot be found during overloading
2374           now mention the correct package name, as they did in 5.8.x, instead
2375           of erroneously mentioning the "overload" package, as they have
2376           since 5.10.0.
2377
2378       •   Undefining %overload:: no longer causes a crash.
2379
2380   Prototypes of built-in keywords
2381       •   The "prototype" function no longer dies for the "__FILE__",
2382           "__LINE__" and "__PACKAGE__" directives.  It now returns an empty-
2383           string prototype for them, because they are syntactically
2384           indistinguishable from nullary functions like "time".
2385
2386       •   "prototype" now returns "undef" for all overridable infix
2387           operators, such as "eq", which are not callable in any way
2388           resembling functions.  It used to return incorrect prototypes for
2389           some and die for others [perl #94984].
2390
2391       •   The prototypes of several built-in functions--"getprotobynumber",
2392           "lock", "not" and "select"--have been corrected, or at least are
2393           now closer to reality than before.
2394
2395   Regular expressions
2396       •   "/[[:ascii:]]/" and "/[[:blank:]]/" now use locale rules under "use
2397           locale" when the platform supports that.  Previously, they used the
2398           platform's native character set.
2399
2400       •   "m/[[:ascii:]]/i" and "/\p{ASCII}/i" now match identically (when
2401           not under a differing locale).  This fixes a regression introduced
2402           in 5.14 in which the first expression could match characters
2403           outside of ASCII, such as the KELVIN SIGN.
2404
2405       •   "/.*/g" would sometimes refuse to match at the end of a string that
2406           ends with "\n".  This has been fixed [perl #109206].
2407
2408       •   Starting with 5.12.0, Perl used to get its internal bookkeeping
2409           muddled up after assigning "${ qr// }" to a hash element and
2410           locking it with Hash::Util.  This could result in double frees,
2411           crashes, or erratic behavior.
2412
2413       •   The new (in 5.14.0) regular expression modifier "/a" when repeated
2414           like "/aa" forbids the characters outside the ASCII range that
2415           match characters inside that range from matching under "/i".  This
2416           did not work under some circumstances, all involving alternation,
2417           such as:
2418
2419            "\N{KELVIN SIGN}" =~ /k|foo/iaa;
2420
2421           succeeded inappropriately.  This is now fixed.
2422
2423       •   5.14.0 introduced some memory leaks in regular expression character
2424           classes such as "[\w\s]", which have now been fixed. (5.14.1)
2425
2426       •   An edge case in regular expression matching could potentially loop.
2427           This happened only under "/i" in bracketed character classes that
2428           have characters with multi-character folds, and the target string
2429           to match against includes the first portion of the fold, followed
2430           by another character that has a multi-character fold that begins
2431           with the remaining portion of the fold, plus some more.
2432
2433            "s\N{U+DF}" =~ /[\x{DF}foo]/i
2434
2435           is one such case.  "\xDF" folds to "ss". (5.14.1)
2436
2437       •   A few characters in regular expression pattern matches did not
2438           match correctly in some circumstances, all involving "/i".  The
2439           affected characters are: COMBINING GREEK YPOGEGRAMMENI, GREEK
2440           CAPITAL LETTER IOTA, GREEK CAPITAL LETTER UPSILON, GREEK
2441           PROSGEGRAMMENI, GREEK SMALL LETTER IOTA WITH DIALYTIKA AND OXIA,
2442           GREEK SMALL LETTER IOTA WITH DIALYTIKA AND TONOS, GREEK SMALL
2443           LETTER UPSILON WITH DIALYTIKA AND OXIA, GREEK SMALL LETTER UPSILON
2444           WITH DIALYTIKA AND TONOS, LATIN SMALL LETTER LONG S, LATIN SMALL
2445           LIGATURE LONG S T, and LATIN SMALL LIGATURE ST.
2446
2447       •   A memory leak regression in regular expression compilation under
2448           threading has been fixed.
2449
2450       •   A regression introduced in 5.14.0 has been fixed.  This involved an
2451           inverted bracketed character class in a regular expression that
2452           consisted solely of a Unicode property.  That property wasn't
2453           getting inverted outside the Latin1 range.
2454
2455       •   Three problematic Unicode characters now work better in regex
2456           pattern matching under "/i".
2457
2458           In the past, three Unicode characters: LATIN SMALL LETTER SHARP S,
2459           GREEK SMALL LETTER IOTA WITH DIALYTIKA AND TONOS, and GREEK SMALL
2460           LETTER UPSILON WITH DIALYTIKA AND TONOS, along with the sequences
2461           that they fold to (including "ss" for LATIN SMALL LETTER SHARP S),
2462           did not properly match under "/i".  5.14.0 fixed some of these
2463           cases, but introduced others, including a panic when one of the
2464           characters or sequences was used in the "(?(DEFINE)" regular
2465           expression predicate.  The known bugs that were introduced in 5.14
2466           have now been fixed; as well as some other edge cases that have
2467           never worked until now.  These all involve using the characters and
2468           sequences outside bracketed character classes under "/i".  This
2469           closes [perl #98546].
2470
2471           There remain known problems when using certain characters with
2472           multi-character folds inside bracketed character classes, including
2473           such constructs as "qr/[\N{LATIN SMALL LETTER SHARP}a-z]/i".  These
2474           remaining bugs are addressed in [perl #89774].
2475
2476       •   RT #78266: The regex engine has been leaking memory when accessing
2477           named captures that weren't matched as part of a regex ever since
2478           5.10 when they were introduced; e.g., this would consume over a
2479           hundred MB of memory:
2480
2481               for (1..10_000_000) {
2482                   if ("foo" =~ /(foo|(?<capture>bar))?/) {
2483                       my $capture = $+{capture}
2484                   }
2485               }
2486               system "ps -o rss $$"'
2487
2488       •   In 5.14, "/[[:lower:]]/i" and "/[[:upper:]]/i" no longer matched
2489           the opposite case.  This has been fixed [perl #101970].
2490
2491       •   A regular expression match with an overloaded object on the right-
2492           hand side would sometimes stringify the object too many times.
2493
2494       •   A regression has been fixed that was introduced in 5.14, in "/i"
2495           regular expression matching, in which a match improperly fails if
2496           the pattern is in UTF-8, the target string is not, and a Latin-1
2497           character precedes a character in the string that should match the
2498           pattern.  [perl #101710]
2499
2500       •   In case-insensitive regular expression pattern matching, no longer
2501           on UTF-8 encoded strings does the scan for the start of match look
2502           only at the first possible position.  This caused matches such as
2503           ""f\x{FB00}" =~ /ff/i" to fail.
2504
2505       •   The regexp optimizer no longer crashes on debugging builds when
2506           merging fixed-string nodes with inconvenient contents.
2507
2508       •   A panic involving the combination of the regular expression
2509           modifiers "/aa" and the "\b" escape sequence introduced in 5.14.0
2510           has been fixed [perl #95964]. (5.14.2)
2511
2512       •   The combination of the regular expression modifiers "/aa" and the
2513           "\b" and "\B" escape sequences did not work properly on UTF-8
2514           encoded strings.  All non-ASCII characters under "/aa" should be
2515           treated as non-word characters, but what was happening was that
2516           Unicode rules were used to determine wordness/non-wordness for non-
2517           ASCII characters.  This is now fixed [perl #95968].
2518
2519       •   "(?foo: ...)" no longer loses passed in character set.
2520
2521       •   The trie optimization used to have problems with alternations
2522           containing an empty "(?:)", causing ""x" =~
2523           /\A(?>(?:(?:)A|B|C?x))\z/" not to match, whereas it should [perl
2524           #111842].
2525
2526       •   Use of lexical ("my") variables in code blocks embedded in regular
2527           expressions will no longer result in memory corruption or crashes.
2528
2529           Nevertheless, these code blocks are still experimental, as there
2530           are still problems with the wrong variables being closed over (in
2531           loops for instance) and with abnormal exiting (e.g., "die") causing
2532           memory corruption.
2533
2534       •   The "\h", "\H", "\v" and "\V" regular expression metacharacters
2535           used to cause a panic error message when trying to match at the end
2536           of the string [perl #96354].
2537
2538       •   The abbreviations for four C1 control characters "MW" "PM", "RI",
2539           and "ST" were previously unrecognized by "\N{}", vianame(), and
2540           string_vianame().
2541
2542       •   Mentioning a variable named "&" other than $& (i.e., "@&" or "%&")
2543           no longer stops $& from working.  The same applies to variables
2544           named "'" and "`" [perl #24237].
2545
2546       •   Creating a "UNIVERSAL::AUTOLOAD" sub no longer stops "%+", "%-" and
2547           "%!" from working some of the time [perl #105024].
2548
2549   Smartmatching
2550       •   "~~" now correctly handles the precedence of Any~~Object, and is
2551           not tricked by an overloaded object on the left-hand side.
2552
2553       •   In Perl 5.14.0, "$tainted ~~ @array" stopped working properly.
2554           Sometimes it would erroneously fail (when $tainted contained a
2555           string that occurs in the array after the first element) or
2556           erroneously succeed (when "undef" occurred after the first element)
2557           [perl #93590].
2558
2559   The "sort" operator
2560       •   "sort" was not treating "sub {}" and "sub {()}" as equivalent when
2561           such a sub was provided as the comparison routine.  It used to
2562           croak on "sub {()}".
2563
2564       •   "sort" now works once more with custom sort routines that are
2565           XSUBs.  It stopped working in 5.10.0.
2566
2567       •   "sort" with a constant for a custom sort routine, although it
2568           produces unsorted results, no longer crashes.  It started crashing
2569           in 5.10.0.
2570
2571       •   Warnings emitted by "sort" when a custom comparison routine returns
2572           a non-numeric value now contain "in sort" and show the line number
2573           of the "sort" operator, rather than the last line of the comparison
2574           routine.  The warnings also now occur only if warnings are enabled
2575           in the scope where "sort" occurs.  Previously the warnings would
2576           occur if enabled in the comparison routine's scope.
2577
2578       •   "sort { $a <=> $b }", which is optimized internally, now produces
2579           "uninitialized" warnings for NaNs (not-a-number values), since
2580           "<=>" returns "undef" for those.  This brings it in line with
2581           "sort { 1; $a <=> $b }" and other more complex cases, which are not
2582           optimized [perl #94390].
2583
2584   The "substr" operator
2585       •   Tied (and otherwise magical) variables are no longer exempt from
2586           the "Attempt to use reference as lvalue in substr" warning.
2587
2588       •   That warning now occurs when the returned lvalue is assigned to,
2589           not when "substr" itself is called.  This makes a difference only
2590           if the return value of "substr" is referenced and later assigned
2591           to.
2592
2593       •   Passing a substring of a read-only value or a typeglob to a
2594           function (potential lvalue context) no longer causes an immediate
2595           "Can't coerce" or "Modification of a read-only value" error.  That
2596           error occurs only if the passed value is assigned to.
2597
2598           The same thing happens with the "substr outside of string" error.
2599           If the lvalue is only read from, not written to, it is now just a
2600           warning, as with rvalue "substr".
2601
2602       •   "substr" assignments no longer call FETCH twice if the first
2603           argument is a tied variable, just once.
2604
2605   Support for embedded nulls
2606       Some parts of Perl did not work correctly with nulls ("chr 0") embedded
2607       in strings.  That meant that, for instance, "$m = "a\0b"; foo->$m"
2608       would call the "a" method, instead of the actual method name contained
2609       in $m.  These parts of perl have been fixed to support nulls:
2610
2611       •   Method names
2612
2613       •   Typeglob names (including filehandle and subroutine names)
2614
2615       •   Package names, including the return value of "ref()"
2616
2617       •   Typeglob elements (*foo{"THING\0stuff"})
2618
2619       •   Signal names
2620
2621       •   Various warnings and error messages that mention variable names or
2622           values, methods, etc.
2623
2624       One side effect of these changes is that blessing into "\0" no longer
2625       causes "ref()" to return false.
2626
2627   Threading bugs
2628       •   Typeglobs returned from threads are no longer cloned if the parent
2629           thread already has a glob with the same name.  This means that
2630           returned subroutines will now assign to the right package variables
2631           [perl #107366].
2632
2633       •   Some cases of threads crashing due to memory allocation during
2634           cloning have been fixed [perl #90006].
2635
2636       •   Thread joining would sometimes emit "Attempt to free unreferenced
2637           scalar" warnings if "caller" had been used from the "DB" package
2638           before thread creation [perl #98092].
2639
2640       •   Locking a subroutine (via "lock &sub") is no longer a compile-time
2641           error for regular subs.  For lvalue subroutines, it no longer tries
2642           to return the sub as a scalar, resulting in strange side effects
2643           like "ref \$_" returning "CODE" in some instances.
2644
2645           "lock &sub" is now a run-time error if threads::shared is loaded (a
2646           no-op otherwise), but that may be rectified in a future version.
2647
2648   Tied variables
2649       •   Various cases in which FETCH was being ignored or called too many
2650           times have been fixed:
2651
2652           •   "PerlIO::get_layers" [perl #97956]
2653
2654           •   "$tied =~ y/a/b/", "chop $tied" and "chomp $tied" when $tied
2655               holds a reference.
2656
2657           •   When calling "local $_" [perl #105912]
2658
2659           •   Four-argument "select"
2660
2661           •   A tied buffer passed to "sysread"
2662
2663           •   "$tied .= <>"
2664
2665           •   Three-argument "open", the third being a tied file handle (as
2666               in "open $fh, ">&", $tied")
2667
2668           •   "sort" with a reference to a tied glob for the comparison
2669               routine.
2670
2671           •   ".." and "..." in list context [perl #53554].
2672
2673           •   "${$tied}", "@{$tied}", "%{$tied}" and "*{$tied}" where the
2674               tied variable returns a string ("&{}" was unaffected)
2675
2676           •   "defined ${ $tied_variable }"
2677
2678           •   Various functions that take a filehandle argument in rvalue
2679               context ("close", "readline", etc.) [perl #97482]
2680
2681           •   Some cases of dereferencing a complex expression, such as "${
2682               (), $tied } = 1", used to call "FETCH" multiple times, but now
2683               call it once.
2684
2685           •   "$tied->method" where $tied returns a package name--even
2686               resulting in a failure to call the method, due to memory
2687               corruption
2688
2689           •   Assignments like "*$tied = \&{"..."}" and "*glob = $tied"
2690
2691           •   "chdir", "chmod", "chown", "utime", "truncate", "stat", "lstat"
2692               and the filetest ops ("-r", "-x", etc.)
2693
2694       •   "caller" sets @DB::args to the subroutine arguments when called
2695           from the DB package.  It used to crash when doing so if @DB::args
2696           happened to be tied.  Now it croaks instead.
2697
2698       •   Tying an element of %ENV or "%^H" and then deleting that element
2699           would result in a call to the tie object's DELETE method, even
2700           though tying the element itself is supposed to be equivalent to
2701           tying a scalar (the element is, of course, a scalar) [perl #67490].
2702
2703       •   When Perl autovivifies an element of a tied array or hash (which
2704           entails calling STORE with a new reference), it now calls FETCH
2705           immediately after the STORE, instead of assuming that FETCH would
2706           have returned the same reference.  This can make it easier to
2707           implement tied objects [perl #35865, #43011].
2708
2709       •   Four-argument "select" no longer produces its "Non-string passed as
2710           bitmask" warning on tied or tainted variables that are strings.
2711
2712       •   Localizing a tied scalar that returns a typeglob no longer stops it
2713           from being tied till the end of the scope.
2714
2715       •   Attempting to "goto" out of a tied handle method used to cause
2716           memory corruption or crashes.  Now it produces an error message
2717           instead [perl #8611].
2718
2719       •   A bug has been fixed that occurs when a tied variable is used as a
2720           subroutine reference:  if the last thing assigned to or returned
2721           from the variable was a reference or typeglob, the "\&$tied" could
2722           either crash or return the wrong subroutine.  The reference case is
2723           a regression introduced in Perl 5.10.0.  For typeglobs, it has
2724           probably never worked till now.
2725
2726   Version objects and vstrings
2727       •   The bitwise complement operator (and possibly other operators, too)
2728           when passed a vstring would leave vstring magic attached to the
2729           return value, even though the string had changed.  This meant that
2730           "version->new(~v1.2.3)" would create a version looking like
2731           "v1.2.3" even though the string passed to "version->new" was
2732           actually "\376\375\374".  This also caused B::Deparse to deparse
2733           "~v1.2.3" incorrectly, without the "~" [perl #29070].
2734
2735       •   Assigning a vstring to a magic (e.g., tied, $!) variable and then
2736           assigning something else used to blow away all magic.  This meant
2737           that tied variables would come undone, $! would stop getting
2738           updated on failed system calls, $| would stop setting autoflush,
2739           and other mischief would take place.  This has been fixed.
2740
2741       •   "version->new("version")" and "printf "%vd", "version"" no longer
2742           crash [perl #102586].
2743
2744       •   Version comparisons, such as those that happen implicitly with "use
2745           v5.43", no longer cause locale settings to change [perl #105784].
2746
2747       •   Version objects no longer cause memory leaks in boolean context
2748           [perl #109762].
2749
2750   Warnings, redefinition
2751       •   Subroutines from the "autouse" namespace are once more exempt from
2752           redefinition warnings.  This used to work in 5.005, but was broken
2753           in 5.6 for most subroutines.  For subs created via XS that redefine
2754           subroutines from the "autouse" package, this stopped working in
2755           5.10.
2756
2757       •   New XSUBs now produce redefinition warnings if they overwrite
2758           existing subs, as they did in 5.8.x.  (The "autouse" logic was
2759           reversed in 5.10-14.  Only subroutines from the "autouse" namespace
2760           would warn when clobbered.)
2761
2762       •   "newCONSTSUB" used to use compile-time warning hints, instead of
2763           run-time hints.  The following code should never produce a
2764           redefinition warning, but it used to, if "newCONSTSUB" redefined an
2765           existing subroutine:
2766
2767               use warnings;
2768               BEGIN {
2769                   no warnings;
2770                   some_XS_function_that_calls_new_CONSTSUB();
2771               }
2772
2773       •   Redefinition warnings for constant subroutines are on by default
2774           (what are known as severe warnings in perldiag).  This occurred
2775           only when it was a glob assignment or declaration of a Perl
2776           subroutine that caused the warning.  If the creation of XSUBs
2777           triggered the warning, it was not a default warning.  This has been
2778           corrected.
2779
2780       •   The internal check to see whether a redefinition warning should
2781           occur used to emit "uninitialized" warnings in cases like this:
2782
2783               use warnings "uninitialized";
2784               use constant {u => undef, v => undef};
2785               sub foo(){u}
2786               sub foo(){v}
2787
2788   Warnings, "Uninitialized"
2789       •   Various functions that take a filehandle argument in rvalue context
2790           ("close", "readline", etc.) used to warn twice for an undefined
2791           handle [perl #97482].
2792
2793       •   "dbmopen" now only warns once, rather than three times, if the mode
2794           argument is "undef" [perl #90064].
2795
2796       •   The "+=" operator does not usually warn when the left-hand side is
2797           "undef", but it was doing so for tied variables.  This has been
2798           fixed [perl #44895].
2799
2800       •   A bug fix in Perl 5.14 introduced a new bug, causing
2801           "uninitialized" warnings to report the wrong variable if the
2802           operator in question had two operands and one was "%{...}" or
2803           "@{...}".  This has been fixed [perl #103766].
2804
2805       •   ".." and "..." in list context now mention the name of the variable
2806           in "uninitialized" warnings for string (as opposed to numeric)
2807           ranges.
2808
2809   Weak references
2810       •   Weakening the first argument to an automatically-invoked "DESTROY"
2811           method could result in erroneous "DESTROY created new reference"
2812           errors or crashes.  Now it is an error to weaken a read-only
2813           reference.
2814
2815       •   Weak references to lexical hashes going out of scope were not going
2816           stale (becoming undefined), but continued to point to the hash.
2817
2818       •   Weak references to lexical variables going out of scope are now
2819           broken before any magical methods (e.g., DESTROY on a tie object)
2820           are called.  This prevents such methods from modifying the variable
2821           that will be seen the next time the scope is entered.
2822
2823       •   Creating a weak reference to an @ISA array or accessing the array
2824           index ($#ISA) could result in confused internal bookkeeping for
2825           elements later added to the @ISA array.  For instance, creating a
2826           weak reference to the element itself could push that weak reference
2827           on to @ISA; and elements added after use of $#ISA would be ignored
2828           by method lookup [perl #85670].
2829
2830   Other notable fixes
2831       •   "quotemeta" now quotes consistently the same non-ASCII characters
2832           under "use feature 'unicode_strings'", regardless of whether the
2833           string is encoded in UTF-8 or not, hence fixing the last vestiges
2834           (we hope) of the notorious "The "Unicode Bug"" in perlunicode.
2835           [perl #77654].
2836
2837           Which of these code points is quoted has changed, based on
2838           Unicode's recommendations.  See "quotemeta" in perlfunc for
2839           details.
2840
2841       •   "study" is now a no-op, presumably fixing all outstanding bugs
2842           related to study causing regex matches to behave incorrectly!
2843
2844       •   When one writes "open foo || die", which used to work in Perl 4, a
2845           "Precedence problem" warning is produced.  This warning used
2846           erroneously to apply to fully-qualified bareword handle names not
2847           followed by "||".  This has been corrected.
2848
2849       •   After package aliasing ("*foo:: = *bar::"), "select" with 0 or 1
2850           argument would sometimes return a name that could not be used to
2851           refer to the filehandle, or sometimes it would return "undef" even
2852           when a filehandle was selected.  Now it returns a typeglob
2853           reference in such cases.
2854
2855       •   "PerlIO::get_layers" no longer ignores some arguments that it
2856           thinks are numeric, while treating others as filehandle names.  It
2857           is now consistent for flat scalars (i.e., not references).
2858
2859       •   Unrecognized switches on "#!" line
2860
2861           If a switch, such as -x, that cannot occur on the "#!" line is used
2862           there, perl dies with "Can't emulate...".
2863
2864           It used to produce the same message for switches that perl did not
2865           recognize at all, whether on the command line or the "#!" line.
2866
2867           Now it produces the "Unrecognized switch" error message [perl
2868           #104288].
2869
2870       •   "system" now temporarily blocks the SIGCHLD signal handler, to
2871           prevent the signal handler from stealing the exit status [perl
2872           #105700].
2873
2874       •   The %n formatting code for "printf" and "sprintf", which causes the
2875           number of characters to be assigned to the next argument, now
2876           actually assigns the number of characters, instead of the number of
2877           bytes.
2878
2879           It also works now with special lvalue functions like "substr" and
2880           with nonexistent hash and array elements [perl #3471, #103492].
2881
2882       •   Perl skips copying values returned from a subroutine, for the sake
2883           of speed, if doing so would make no observable difference.  Because
2884           of faulty logic, this would happen with the result of "delete",
2885           "shift" or "splice", even if the result was referenced elsewhere.
2886           It also did so with tied variables about to be freed [perl #91844,
2887           #95548].
2888
2889       •   "utf8::decode" now refuses to modify read-only scalars [perl
2890           #91850].
2891
2892       •   Freeing $_ inside a "grep" or "map" block, a code block embedded in
2893           a regular expression, or an @INC filter (a subroutine returned by a
2894           subroutine in @INC) used to result in double frees or crashes [perl
2895           #91880, #92254, #92256].
2896
2897       •   "eval" returns "undef" in scalar context or an empty list in list
2898           context when there is a run-time error.  When "eval" was passed a
2899           string in list context and a syntax error occurred, it used to
2900           return a list containing a single undefined element.  Now it
2901           returns an empty list in list context for all errors [perl #80630].
2902
2903       •   "goto &func" no longer crashes, but produces an error message, when
2904           the unwinding of the current subroutine's scope fires a destructor
2905           that undefines the subroutine being "goneto" [perl #99850].
2906
2907       •   Perl now holds an extra reference count on the package that code is
2908           currently compiling in.  This means that the following code no
2909           longer crashes [perl #101486]:
2910
2911               package Foo;
2912               BEGIN {*Foo:: = *Bar::}
2913               sub foo;
2914
2915       •   The "x" repetition operator no longer crashes on 64-bit builds with
2916           large repeat counts [perl #94560].
2917
2918       •   Calling "require" on an implicit $_ when *CORE::GLOBAL::require has
2919           been overridden does not segfault anymore, and $_ is now passed to
2920           the overriding subroutine [perl #78260].
2921
2922       •   "use" and "require" are no longer affected by the I/O layers active
2923           in the caller's scope (enabled by open.pm) [perl #96008].
2924
2925       •   "our $::e; $e" (which is invalid) no longer produces the
2926           "Compilation error at lib/utf8_heavy.pl..." error message, which it
2927           started emitting in 5.10.0 [perl #99984].
2928
2929       •   On 64-bit systems, "read()" now understands large string offsets
2930           beyond the 32-bit range.
2931
2932       •   Errors that occur when processing subroutine attributes no longer
2933           cause the subroutine's op tree to leak.
2934
2935       •   Passing the same constant subroutine to both "index" and "formline"
2936           no longer causes one or the other to fail [perl #89218]. (5.14.1)
2937
2938       •   List assignment to lexical variables declared with attributes in
2939           the same statement ("my ($x,@y) : blimp = (72,94)") stopped working
2940           in Perl 5.8.0.  It has now been fixed.
2941
2942       •   Perl 5.10.0 introduced some faulty logic that made "U*" in the
2943           middle of a pack template equivalent to "U0" if the input string
2944           was empty.  This has been fixed [perl #90160]. (5.14.2)
2945
2946       •   Destructors on objects were not called during global destruction on
2947           objects that were not referenced by any scalars.  This could happen
2948           if an array element were blessed (e.g., "bless \$a[0]") or if a
2949           closure referenced a blessed variable ("bless \my @a; sub foo { @a
2950           }").
2951
2952           Now there is an extra pass during global destruction to fire
2953           destructors on any objects that might be left after the usual
2954           passes that check for objects referenced by scalars [perl #36347].
2955
2956       •   Fixed a case where it was possible that a freed buffer may have
2957           been read from when parsing a here document [perl #90128]. (5.14.1)
2958
2959       •   "each(ARRAY)" is now wrapped in "defined(...)", like "each(HASH)",
2960           inside a "while" condition [perl #90888].
2961
2962       •   A problem with context propagation when a "do" block is an argument
2963           to "return" has been fixed.  It used to cause "undef" to be
2964           returned in certain cases of a "return" inside an "if" block which
2965           itself is followed by another "return".
2966
2967       •   Calling "index" with a tainted constant no longer causes constants
2968           in subsequently compiled code to become tainted [perl #64804].
2969
2970       •   Infinite loops like "1 while 1" used to stop "strict 'subs'" mode
2971           from working for the rest of the block.
2972
2973       •   For list assignments like "($a,$b) = ($b,$a)", Perl has to make a
2974           copy of the items on the right-hand side before assignment them to
2975           the left.  For efficiency's sake, it assigns the values on the
2976           right straight to the items on the left if no one variable is
2977           mentioned on both sides, as in "($a,$b) = ($c,$d)".  The logic for
2978           determining when it can cheat was faulty, in that "&&" and "||" on
2979           the right-hand side could fool it.  So "($a,$b) = $some_true_value
2980           && ($b,$a)" would end up assigning the value of $b to both scalars.
2981
2982       •   Perl no longer tries to apply lvalue context to the string in
2983           "("string", $variable) ||= 1" (which used to be an error).  Since
2984           the left-hand side of "||=" is evaluated in scalar context, that's
2985           a scalar comma operator, which gives all but the last item void
2986           context.  There is no such thing as void lvalue context, so it was
2987           a mistake for Perl to try to force it [perl #96942].
2988
2989       •   "caller" no longer leaks memory when called from the DB package if
2990           @DB::args was assigned to after the first call to "caller".  Carp
2991           was triggering this bug [perl #97010]. (5.14.2)
2992
2993       •   "close" and similar filehandle functions, when called on built-in
2994           global variables (like $+), used to die if the variable happened to
2995           hold the undefined value, instead of producing the usual "Use of
2996           uninitialized value" warning.
2997
2998       •   When autovivified file handles were introduced in Perl 5.6.0,
2999           "readline" was inadvertently made to autovivify when called as
3000           "readline($foo)" (but not as "<$foo>").  It has now been fixed
3001           never to autovivify.
3002
3003       •   Calling an undefined anonymous subroutine (e.g., what $x holds
3004           after "undef &{$x = sub{}}") used to cause a "Not a CODE reference"
3005           error, which has been corrected to "Undefined subroutine called"
3006           [perl #71154].
3007
3008       •   Causing @DB::args to be freed between uses of "caller" no longer
3009           results in a crash [perl #93320].
3010
3011       •   "setpgrp($foo)" used to be equivalent to "($foo, setpgrp)", because
3012           "setpgrp" was ignoring its argument if there was just one.  Now it
3013           is equivalent to "setpgrp($foo,0)".
3014
3015       •   "shmread" was not setting the scalar flags correctly when reading
3016           from shared memory, causing the existing cached numeric
3017           representation in the scalar to persist [perl #98480].
3018
3019       •   "++" and "--" now work on copies of globs, instead of dying.
3020
3021       •   "splice()" doesn't warn when truncating
3022
3023           You can now limit the size of an array using "splice(@a,MAX_LEN)"
3024           without worrying about warnings.
3025
3026       •   $$ is no longer tainted.  Since this value comes directly from
3027           "getpid()", it is always safe.
3028
3029       •   The parser no longer leaks a filehandle if STDIN was closed before
3030           parsing started [perl #37033].
3031
3032       •   "die;" with a non-reference, non-string, or magical (e.g., tainted)
3033           value in $@ now properly propagates that value [perl #111654].
3034

Known Problems

3036       •   On Solaris, we have two kinds of failure.
3037
3038           If make is Sun's make, we get an error about a badly formed macro
3039           assignment in the Makefile.  That happens when ./Configure tries to
3040           make depends.  Configure then exits 0, but further make-ing fails.
3041
3042           If make is gmake, Configure completes, then we get errors related
3043           to /usr/include/stdbool.h
3044
3045       •   On Win32, a number of tests hang unless STDERR is redirected.  The
3046           cause of this is still under investigation.
3047
3048       •   When building as root with a umask that prevents files from being
3049           other-readable, t/op/filetest.t will fail.  This is a test bug, not
3050           a bug in perl's behavior.
3051
3052       •   Configuring with a recent gcc and link-time-optimization, such as
3053           "Configure -Doptimize='-O2 -flto'" fails because the optimizer
3054           optimizes away some of Configure's tests.  A workaround is to omit
3055           the "-flto" flag when running Configure, but add it back in while
3056           actually building, something like
3057
3058               sh Configure -Doptimize=-O2
3059               make OPTIMIZE='-O2 -flto'
3060
3061       •   The following CPAN modules have test failures with perl 5.16.
3062           Patches have been submitted for all of these, so hopefully there
3063           will be new releases soon:
3064
3065           •   Date::Pcalc version 6.1
3066
3067           •   Module::CPANTS::Analyse version 0.85
3068
3069               This fails due to problems in Module::Find 0.10 and
3070               File::MMagic 1.27.
3071
3072           •   PerlIO::Util version 0.72
3073

Acknowledgements

3075       Perl 5.16.0 represents approximately 12 months of development since
3076       Perl 5.14.0 and contains approximately 590,000 lines of changes across
3077       2,500 files from 139 authors.
3078
3079       Perl continues to flourish into its third decade thanks to a vibrant
3080       community of users and developers.  The following people are known to
3081       have contributed the improvements that became Perl 5.16.0:
3082
3083       Aaron Crane, Abhijit Menon-Sen, Abigail, Alan Haggai Alavi, Alberto
3084       Simo~es, Alexandr Ciornii, Andreas Koenig, Andy Dougherty, Aristotle
3085       Pagaltzis, Bo Johansson, Bo Lindbergh, Breno G. de Oliveira, brian d
3086       foy, Brian Fraser, Brian Greenfield, Carl Hayter, Chas. Owens, Chia-
3087       liang Kao, Chip Salzenberg, Chris 'BinGOs' Williams, Christian Hansen,
3088       Christopher J. Madsen, chromatic, Claes Jacobsson, Claudio Ramirez,
3089       Craig A. Berry, Damian Conway, Daniel Kahn Gillmor, Darin McBride, Dave
3090       Rolsky, David Cantrell, David Golden, David Leadbeater, David Mitchell,
3091       Dee Newcum, Dennis Kaarsemaker, Dominic Hargreaves, Douglas Christopher
3092       Wilson, Eric Brine, Father Chrysostomos, Florian Ragwitz, Frederic
3093       Briere, George Greer, Gerard Goossen, Gisle Aas, H.Merijn Brand, Hojung
3094       Youn, Ian Goodacre, James E Keenan, Jan Dubois, Jerry D. Hedden, Jesse
3095       Luehrs, Jesse Vincent, Jilles Tjoelker, Jim Cromie, Jim Meyering, Joel
3096       Berger, Johan Vromans, Johannes Plunien, John Hawkinson, John P.
3097       Linderman, John Peacock, Joshua ben Jore, Juerd Waalboer, Karl
3098       Williamson, Karthik Rajagopalan, Keith Thompson, Kevin J.  Woolley,
3099       Kevin Ryde, Laurent Dami, Leo Lapworth, Leon Brocard, Leon Timmermans,
3100       Louis Strous, Lukas Mai, Marc Green, Marcel Gruenauer, Mark A.
3101       Stratman, Mark Dootson, Mark Jason Dominus, Martin Hasch, Matthew
3102       Horsfall, Max Maischein, Michael G Schwern, Michael Witten, Mike
3103       Sheldrake, Moritz Lenz, Nicholas Clark, Niko Tyni, Nuno Carvalho, Pau
3104       Amma, Paul Evans, Paul Green, Paul Johnson, Perlover, Peter John
3105       Acklam, Peter Martini, Peter Scott, Phil Monsen, Pino Toscano, Rafael
3106       Garcia-Suarez, Rainer Tammer, Reini Urban, Ricardo Signes, Robin
3107       Barker, Rodolfo Carvalho, Salvador Fandin~o, Sam Kimbrel, Samuel
3108       Thibault, Shawn M Moore, Shigeya Suzuki, Shirakata Kentaro, Shlomi
3109       Fish, Sisyphus, Slaven Rezic, Spiros Denaxas, Steffen Mueller, Steffen
3110       Schwigon, Stephen Bennett, Stephen Oberholtzer, Stevan Little, Steve
3111       Hay, Steve Peters, Thomas Sibley, Thorsten Glaser, Timothe Litt, Todd
3112       Rinaldo, Tom Christiansen, Tom Hukins, Tony Cook, Vadim Konovalov,
3113       Vincent Pit, Vladimir Timofeev, Walt Mankowski, Yves Orton, Zefram,
3114       Zsban Ambrus, AEvar Arnfjoerd` Bjarmason.
3115
3116       The list above is almost certainly incomplete as it is automatically
3117       generated from version control history.  In particular, it does not
3118       include the names of the (very much appreciated) contributors who
3119       reported issues to the Perl bug tracker.
3120
3121       Many of the changes included in this version originated in the CPAN
3122       modules included in Perl's core.  We're grateful to the entire CPAN
3123       community for helping Perl to flourish.
3124
3125       For a more complete list of all of Perl's historical contributors,
3126       please see the AUTHORS file in the Perl source distribution.
3127

Reporting Bugs

3129       If you find what you think is a bug, you might check the articles
3130       recently posted to the comp.lang.perl.misc newsgroup and the perl bug
3131       database at <http://rt.perl.org/perlbug/>.  There may also be
3132       information at <http://www.perl.org/>, the Perl Home Page.
3133
3134       If you believe you have an unreported bug, please run the perlbug
3135       program included with your release.  Be sure to trim your bug down to a
3136       tiny but sufficient test case.  Your bug report, along with the output
3137       of "perl -V", will be sent off to perlbug@perl.org to be analysed by
3138       the Perl porting team.
3139
3140       If the bug you are reporting has security implications, which make it
3141       inappropriate to send to a publicly archived mailing list, then please
3142       send it to perl5-security-report@perl.org.  This points to a closed
3143       subscription unarchived mailing list, which includes all core
3144       committers, who will be able to help assess the impact of issues,
3145       figure out a resolution, and help co-ordinate the release of patches to
3146       mitigate or fix the problem across all platforms on which Perl is
3147       supported.  Please use this address only for security issues in the
3148       Perl core, not for modules independently distributed on CPAN.
3149

SEE ALSO

3151       The Changes file for an explanation of how to view exhaustive details
3152       on what changed.
3153
3154       The INSTALL file for how to build Perl.
3155
3156       The README file for general stuff.
3157
3158       The Artistic and Copying files for copyright information.
3159
3160
3161
3162perl v5.34.1                      2022-03-15                  PERL5160DELTA(1)
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