1PERLDEPRECATION(1) Perl Programmers Reference Guide PERLDEPRECATION(1)
2
6 perldeprecation - list Perl deprecations
7
9 The purpose of this document is to document what has been deprecated in
10 Perl, and by which version the deprecated feature will disappear, or,
11 for already removed features, when it was removed.
12 This document will try to discuss what alternatives for the deprecated
14 features are available.
15 The deprecated features will be grouped by the version of Perl in which
17 they will be removed.
18 Unscheduled Deprecations
20 Unicode Delimiter Will be Paired
21 Some unicode delimiters used to be allowed as single characters but in
23 the future will be part of a ballanced pair. This deprecation category
24 is used to mark the ones that will change from being unpaired, to
25 paired.
26 Category: "deprecated::delimiter_will_be_paired"
28 Dot In Inc
30 The current working direct "." used to be automatically included in
32 @INC, but in Perl 5.26 this was removed for security reasons. Ever
33 since then we have produced a warning when a user uses "do EXPR" and
34 "EXPR" does not include a path, and the file was not found in any
35 directory in @INC but was located ".". The file will not be loaded but
36 a deprecated warning will be generated.
37 Category: "deprecated::dot_in_inc"
39 Goto Block Construct
41 "goto LABEL;" will produce a deprecated warning when jumping into the
43 body of a loop or other block construct from outside. For instance
44 while (should_loop($x)) {
46 LABEL:
47 do_stuff();
48 }
49 goto LABEL;
50 will produce a warning that this behavior is deprecated. In general you
52 should just avoid doing this, the people that maintain your code will
53 be grateful for your restraint.
54 Category: "deprecated::goto_construct"
56 Unicode Property Name
58 Various types of unicode property name will generate deprecated
60 warnings when used in a regex pattern. For instance surrogate
61 characters will result in deprecation warnings.
62 Category: "deprecated::unicode_property_name"
64 Perl 5.42
66 Smartmatch
67 Smartmatch is now seen as a failed experiment and was marked as
69 deprecated in Perl 5.37.10. This includes the "when" and "given"
70 keywords, as well as the smartmatch operator "~~". The feature will be
71 removed entirely in the Perl 5.42.0 production release.
72 Category: "deprecated::smartmatch"
74 Use of "'" as a global name separator.
76 Perl allows use of "'" instead of "::" to replace the parts of a
78 package or global variable name, for example "A::B" and "A'B" are
79 equivalent.
80 "'" will no longer be recognized as a name separator in Perl 5.42.
82 Category: "deprecated::apostrophe_as_package_separator"
84 Perl 5.40
86 Downgrading a "use VERSION" to below v5.11
87 Once Perl has seen a "use VERSION" declaration that requests a version
89 "v5.11" or above, a subsequent second declaration that requests an
90 earlier version will print a deprecation warning. For example,
91 use v5.14;
93 say "We can use v5.14's features here";
94 use v5.10; # This prints a warning
96 This behaviour will be removed in Perl 5.40; such a subsequent request
98 will become a compile-time error.
99 This is because of an intended related change to the interaction
101 between "use VERSION" and "use strict". If you specify a version >=
102 5.11, strict is enabled implicitly. If you request a version < 5.11,
103 strict will become disabled even if you had previously written "use
104 strict". This was not the previous behaviour of "use VERSION", which at
105 present will track explicitly-enabled strictness flags independently.
106 Category: "deprecated::version_downgrade"
108 Perl 5.38
110 Pod::Html utility functions
111 The definition and documentation of three utility functions previously
113 importable from Pod::Html were moved to new package Pod::Html::Util in
114 Perl 5.36. While they remain importable from Pod::Html in Perl 5.36,
115 as of Perl 5.38 they will only be importable, on request, from
116 Pod::Html::Util.
117 Perl 5.34
119 There were no deprecations or fatalizations in Perl 5.34.
120 Perl 5.32
122 Constants from lexical variables potentially modified elsewhere
123 You wrote something like
125 my $var;
127 $sub = sub () { $var };
128 but $var is referenced elsewhere and could be modified after the "sub"
130 expression is evaluated. Either it is explicitly modified elsewhere
131 ("$var = 3") or it is passed to a subroutine or to an operator like
132 "printf" or "map", which may or may not modify the variable.
133 Traditionally, Perl has captured the value of the variable at that
135 point and turned the subroutine into a constant eligible for inlining.
136 In those cases where the variable can be modified elsewhere, this
137 breaks the behavior of closures, in which the subroutine captures the
138 variable itself, rather than its value, so future changes to the
139 variable are reflected in the subroutine's return value.
140 If you intended for the subroutine to be eligible for inlining, then
142 make sure the variable is not referenced elsewhere, possibly by copying
143 it:
144 my $var2 = $var;
146 $sub = sub () { $var2 };
147 If you do want this subroutine to be a closure that reflects future
149 changes to the variable that it closes over, add an explicit "return":
150 my $var;
152 $sub = sub () { return $var };
153 This usage was deprecated and as of Perl 5.32 is no longer allowed.
155 Use of strings with code points over 0xFF as arguments to "vec"
157 "vec" views its string argument as a sequence of bits. A string
159 containing a code point over 0xFF is nonsensical. This usage is
160 deprecated in Perl 5.28, and was removed in Perl 5.32.
161 Use of code points over 0xFF in string bitwise operators
163 The string bitwise operators, "&", "|", "^", and "~", treat their
165 operands as strings of bytes. As such, values above 0xFF are
166 nonsensical. Some instances of these have been deprecated since Perl
167 5.24, and were made fatal in 5.28, but it turns out that in cases where
168 the wide characters did not affect the end result, no deprecation
169 notice was raised, and so remain legal. Now, all occurrences either
170 are fatal or raise a deprecation warning, so that the remaining legal
171 occurrences became fatal in 5.32.
172 An example of this is
174 "" & "\x{100}"
176 The wide character is not used in the "&" operation because the left
178 operand is shorter. This now throws an exception.
179 hostname() doesn't accept any arguments
181 The function hostname() in the Sys::Hostname module has always been
183 documented to be called with no arguments. Historically it has not
184 enforced this, and has actually accepted and ignored any arguments. As
185 a result, some users have got the mistaken impression that an argument
186 does something useful. To avoid these bugs, the function is being made
187 strict. Passing arguments was deprecated in Perl 5.28 and became fatal
188 in Perl 5.32.
189 Unescaped left braces in regular expressions
191 The simple rule to remember, if you want to match a literal "{"
193 character (U+007B "LEFT CURLY BRACKET") in a regular expression
194 pattern, is to escape each literal instance of it in some way.
195 Generally easiest is to precede it with a backslash, like "\{" or
196 enclose it in square brackets ("[{]"). If the pattern delimiters are
197 also braces, any matching right brace ("}") should also be escaped to
198 avoid confusing the parser, for example,
199 qr{abc\{def\}ghi}
201 Forcing literal "{" characters to be escaped will enable the Perl
203 language to be extended in various ways in future releases. To avoid
204 needlessly breaking existing code, the restriction is not enforced in
205 contexts where there are unlikely to ever be extensions that could
206 conflict with the use there of "{" as a literal. A non-deprecation
207 warning that the left brace is being taken literally is raised in
208 contexts where there could be confusion about it.
209 Literal uses of "{" were deprecated in Perl 5.20, and some uses of it
211 started to give deprecation warnings since. These cases were made fatal
212 in Perl 5.26. Due to an oversight, not all cases of a use of a literal
213 "{" got a deprecation warning. Some cases started warning in Perl
214 5.26, and were made fatal in Perl 5.30. Other cases started in Perl
215 5.28, and were made fatal in 5.32.
216 In XS code, use of various macros dealing with UTF-8.
218 The macros below now require an extra parameter than in versions prior
220 to Perl 5.32. The final parameter in each one is a pointer into the
221 string supplied by the first parameter beyond which the input will not
222 be read. This prevents potential reading beyond the end of the buffer.
223 "isALPHANUMERIC_utf8", "isASCII_utf8", "isBLANK_utf8", "isCNTRL_utf8",
224 "isDIGIT_utf8", "isIDFIRST_utf8", "isPSXSPC_utf8", "isSPACE_utf8",
225 "isVERTWS_utf8", "isWORDCHAR_utf8", "isXDIGIT_utf8",
226 "isALPHANUMERIC_LC_utf8", "isALPHA_LC_utf8", "isASCII_LC_utf8",
227 "isBLANK_LC_utf8", "isCNTRL_LC_utf8", "isDIGIT_LC_utf8",
228 "isGRAPH_LC_utf8", "isIDCONT_LC_utf8", "isIDFIRST_LC_utf8",
229 "isLOWER_LC_utf8", "isPRINT_LC_utf8", "isPSXSPC_LC_utf8",
230 "isPUNCT_LC_utf8", "isSPACE_LC_utf8", "isUPPER_LC_utf8",
231 "isWORDCHAR_LC_utf8", "isXDIGIT_LC_utf8", "toFOLD_utf8",
232 "toLOWER_utf8", "toTITLE_utf8", and "toUPPER_utf8".
233 Since Perl 5.26, this functionality with the extra parameter has been
235 available by using a corresponding macro to each one of these, and
236 whose name is formed by appending "_safe" to the base name. There is
237 no change to the functionality of those. For example,
238 "isDIGIT_utf8_safe" corresponds to "isDIGIT_utf8", and both now behave
239 identically. All are documented in "Character case changing" in
240 perlapi and "Character classification" in perlapi.
241 This change was originally scheduled for 5.30, but was delayed until
243 5.32.
244 File::Glob::glob() was removed
246 "File::Glob" has a function called "glob", which just calls "bsd_glob".
248 File::Glob::glob() was deprecated in Perl 5.8. A deprecation message
250 was issued from Perl 5.26 onwards, the function became fatal in Perl
251 5.30, and was removed entirely in Perl 5.32.
252 Code using File::Glob::glob() should call File::Glob::bsd_glob()
254 instead.
255 Perl 5.30
257 $* is no longer supported
258 Before Perl 5.10, setting $* to a true value globally enabled multi-
260 line matching within a string. This relique from the past lost its
261 special meaning in 5.10. Use of this variable became a fatal error in
262 Perl 5.30, freeing the variable up for a future special meaning.
263 To enable multiline matching one should use the "/m" regexp modifier
265 (possibly in combination with "/s"). This can be set on a per match
266 bases, or can be enabled per lexical scope (including a whole file)
267 with "use re '/m'".
268 $# is no longer supported
270 This variable used to have a special meaning -- it could be used to
272 control how numbers were formatted when printed. This seldom used
273 functionality was removed in Perl 5.10. In order to free up the
274 variable for a future special meaning, its use became a fatal error in
275 Perl 5.30.
276 To specify how numbers are formatted when printed, one is advised to
278 use "printf" or "sprintf" instead.
279 Assigning non-zero to $[ is fatal
281 This variable (and the corresponding "array_base" feature and arybase
283 module) allowed changing the base for array and string indexing
284 operations.
285 Setting this to a non-zero value has been deprecated since Perl 5.12
287 and throws a fatal error as of Perl 5.30.
288 File::Glob::glob() will disappear
290 "File::Glob" has a function called "glob", which just calls "bsd_glob".
292 However, its prototype is different from the prototype of "CORE::glob",
293 and hence, "File::Glob::glob" should not be used.
294 File::Glob::glob() was deprecated in Perl 5.8. A deprecation message
296 was issued from Perl 5.26 onwards, and in Perl 5.30 this was turned
297 into a fatal error.
298 Code using File::Glob::glob() should call File::Glob::bsd_glob()
300 instead.
301 Unescaped left braces in regular expressions (for 5.30)
303 See "Unescaped left braces in regular expressions" above.
305 Unqualified dump()
307 Use of dump() instead of CORE::dump() was deprecated in Perl 5.8, and
309 an unqualified dump() is no longer available as of Perl 5.30.
310 See "dump" in perlfunc.
312 Using my() in false conditional.
314 There has been a long-standing bug in Perl that causes a lexical
316 variable not to be cleared at scope exit when its declaration includes
317 a false conditional. Some people have exploited this bug to achieve a
318 kind of static variable. To allow us to fix this bug, people should
319 not be relying on this behavior.
320 Instead, it's recommended one uses "state" variables to achieve the
322 same effect:
323 use 5.10.0;
325 sub count {state $counter; return ++ $counter}
326 say count (); # Prints 1
327 say count (); # Prints 2
328 "state" variables were introduced in Perl 5.10.
330 Alternatively, you can achieve a similar static effect by declaring the
332 variable in a separate block outside the function, e.g.,
333 sub f { my $x if 0; return $x++ }
335 becomes
337 { my $x; sub f { return $x++ } }
339 The use of my() in a false conditional has been deprecated in Perl
341 5.10, and became a fatal error in Perl 5.30.
342 Reading/writing bytes from/to :utf8 handles.
344 The sysread(), recv(), syswrite() and send() operators are deprecated
346 on handles that have the ":utf8" layer, either explicitly, or
347 implicitly, eg., with the :encoding(UTF-16LE) layer.
348 Both sysread() and recv() currently use only the ":utf8" flag for the
350 stream, ignoring the actual layers. Since sysread() and recv() do no
351 UTF-8 validation they can end up creating invalidly encoded scalars.
352 Similarly, syswrite() and send() use only the ":utf8" flag, otherwise
354 ignoring any layers. If the flag is set, both write the value UTF-8
355 encoded, even if the layer is some different encoding, such as the
356 example above.
357 Ideally, all of these operators would completely ignore the ":utf8"
359 state, working only with bytes, but this would result in silently
360 breaking existing code. To avoid this a future version of perl will
361 throw an exception when any of sysread(), recv(), syswrite() or send()
362 are called on handle with the ":utf8" layer.
363 As of Perl 5.30, it is no longer be possible to use sysread(), recv(),
365 syswrite() or send() to read or send bytes from/to :utf8 handles.
366 Use of unassigned code point or non-standalone grapheme for a
368 delimiter.
369 A grapheme is what appears to a native-speaker of a language to be a
371 character. In Unicode (and hence Perl) a grapheme may actually be
372 several adjacent characters that together form a complete grapheme.
373 For example, there can be a base character, like "R" and an accent,
374 like a circumflex "^", that appear to be a single character when
375 displayed, with the circumflex hovering over the "R".
376 As of Perl 5.30, use of delimiters which are non-standalone graphemes
378 is fatal, in order to move the language to be able to accept multi-
379 character graphemes as delimiters.
380 Also, as of Perl 5.30, delimiters which are unassigned code points but
382 that may someday become assigned are prohibited. Otherwise, code that
383 works today would fail to compile if the currently unassigned delimiter
384 ends up being something that isn't a stand-alone grapheme. Because
385 Unicode is never going to assign non-character code points, nor code
386 points that are above the legal Unicode maximum, those can be
387 delimiters.
388 Perl 5.28
390 Attributes ":locked" and ":unique"
391 The attributes ":locked" (on code references) and ":unique" (on array,
393 hash and scalar references) have had no effect since Perl 5.005 and
394 Perl 5.8.8 respectively. Their use has been deprecated since.
395 As of Perl 5.28, these attributes are syntax errors. Since the
397 attributes do not do anything, removing them from your code fixes the
398 syntax error; and removing them will not influence the behaviour of
399 your code.
400 Bare here-document terminators
402 Perl has allowed you to use a bare here-document terminator to have the
404 here-document end at the first empty line. This practise was deprecated
405 in Perl 5.000; as of Perl 5.28, using a bare here-document terminator
406 throws a fatal error.
407 You are encouraged to use the explicitly quoted form if you wish to use
409 an empty line as the terminator of the here-document:
410 print <<"";
412 Print this line.
413 # Previous blank line ends the here-document.
415 Setting $/ to a reference to a non-positive integer
417 You assigned a reference to a scalar to $/ where the referenced item is
419 not a positive integer. In older perls this appeared to work the same
420 as setting it to "undef" but was in fact internally different, less
421 efficient and with very bad luck could have resulted in your file being
422 split by a stringified form of the reference.
423 In Perl 5.20.0 this was changed so that it would be exactly the same as
425 setting $/ to undef, with the exception that this warning would be
426 thrown.
427 As of Perl 5.28, setting $/ to a reference of a non-positive integer
429 throws a fatal error.
430 You are recommended to change your code to set $/ to "undef" explicitly
432 if you wish to slurp the file.
433 Limit on the value of Unicode code points.
435 Unicode only allows code points up to 0x10FFFF, but Perl allows much
437 larger ones. Up till Perl 5.28, it was allowed to use code points
438 exceeding the maximum value of an integer ("IV_MAX"). However, that
439 did break the perl interpreter in some constructs, including causing it
440 to hang in a few cases. The known problem areas were in "tr///",
441 regular expression pattern matching using quantifiers, as quote
442 delimiters in "qX...X" (where X is the chr() of a large code point),
443 and as the upper limits in loops.
444 The use of out of range code points was deprecated in Perl 5.24; as of
446 Perl 5.28 using a code point exceeding "IV_MAX" throws a fatal error.
447 If your code is to run on various platforms, keep in mind that the
449 upper limit depends on the platform. It is much larger on 64-bit word
450 sizes than 32-bit ones. For 32-bit integers, "IV_MAX" equals
451 0x7FFFFFFF, for 64-bit integers, "IV_MAX" equals 0x7FFFFFFFFFFFFFFF.
452 Use of comma-less variable list in formats.
454 It was allowed to use a list of variables in a format, without
456 separating them with commas. This usage has been deprecated for a long
457 time, and as of Perl 5.28, this throws a fatal error.
458 Use of "\N{}"
460 Use of "\N{}" with nothing between the braces was deprecated in Perl
462 5.24, and throws a fatal error as of Perl 5.28.
463 Since such a construct is equivalent to using an empty string, you are
465 recommended to remove such "\N{}" constructs.
466 Using the same symbol to open a filehandle and a dirhandle
468 It used to be legal to use open() to associate both a filehandle and a
470 dirhandle to the same symbol (glob or scalar). This idiom is likely to
471 be confusing, and it was deprecated in Perl 5.10.
472 Using the same symbol to open() a filehandle and a dirhandle throws a
474 fatal error as of Perl 5.28.
475 You should be using two different symbols instead.
477 ${^ENCODING} is no longer supported.
479 The special variable "${^ENCODING}" was used to implement the
481 "encoding" pragma. Setting this variable to anything other than "undef"
482 was deprecated in Perl 5.22. Full deprecation of the variable happened
483 in Perl 5.25.3.
484 Setting this variable to anything other than an undefined value throws
486 a fatal error as of Perl 5.28.
487 "B::OP::terse"
489 This method, which just calls "B::Concise::b_terse", has been
491 deprecated, and disappeared in Perl 5.28. Please use "B::Concise"
492 instead.
493 Use of inherited AUTOLOAD for non-method %s::%s() is no longer allowed
495 As an (ahem) accidental feature, "AUTOLOAD" subroutines were looked up
497 as methods (using the @ISA hierarchy) even when the subroutines to be
498 autoloaded were called as plain functions (e.g. Foo::bar()), not as
499 methods (e.g. "Foo->bar()" or "$obj->bar()").
500 This bug was deprecated in Perl 5.004, has been rectified in Perl 5.28
502 by using method lookup only for methods' "AUTOLOAD"s.
503 The simple rule is: Inheritance will not work when autoloading non-
505 methods. The simple fix for old code is: In any module that used to
506 depend on inheriting "AUTOLOAD" for non-methods from a base class named
507 "BaseClass", execute "*AUTOLOAD = \&BaseClass::AUTOLOAD" during
508 startup.
509 In code that currently says "use AutoLoader; @ISA = qw(AutoLoader);"
511 you should remove AutoLoader from @ISA and change "use AutoLoader;" to
512 "use AutoLoader 'AUTOLOAD';".
513 Use of code points over 0xFF in string bitwise operators
515 The string bitwise operators, "&", "|", "^", and "~", treat their
517 operands as strings of bytes. As such, values above 0xFF are
518 nonsensical. Using such code points with these operators was deprecated
519 in Perl 5.24, and is fatal as of Perl 5.28.
520 In XS code, use of to_utf8_case()
522 This function has been removed as of Perl 5.28; instead convert to call
524 the appropriate one of: "toFOLD_utf8_safe". "toLOWER_utf8_safe",
525 "toTITLE_utf8_safe", or "toUPPER_utf8_safe".
526 Perl 5.26
528 "--libpods" in "Pod::Html"
529 Since Perl 5.18, the option "--libpods" has been deprecated, and using
531 this option did not do anything other than producing a warning.
532 The "--libpods" option is no longer recognized as of Perl 5.26.
534 The utilities "c2ph" and "pstruct"
536 These old, perl3-era utilities have been deprecated in favour of "h2xs"
538 for a long time. As of Perl 5.26, they have been removed.
539 Trapping "$SIG {__DIE__}" other than during program exit.
541 The $SIG{__DIE__} hook is called even inside an eval(). It was never
543 intended to happen this way, but an implementation glitch made this
544 possible. This used to be deprecated, as it allowed strange action at a
545 distance like rewriting a pending exception in $@. Plans to rectify
546 this have been scrapped, as users found that rewriting a pending
547 exception is actually a useful feature, and not a bug.
548 Perl never issued a deprecation warning for this; the deprecation was
550 by documentation policy only. But this deprecation has been lifted as
551 of Perl 5.26.
552 Malformed UTF-8 string in "%s"
554 This message indicates a bug either in the Perl core or in XS code.
556 Such code was trying to find out if a character, allegedly stored
557 internally encoded as UTF-8, was of a given type, such as being
558 punctuation or a digit. But the character was not encoded in legal
559 UTF-8. The %s is replaced by a string that can be used by
560 knowledgeable people to determine what the type being checked against
561 was.
562 Passing malformed strings was deprecated in Perl 5.18, and became fatal
564 in Perl 5.26.
565 Perl 5.24
567 Use of *glob{FILEHANDLE}
568 The use of *glob{FILEHANDLE} was deprecated in Perl 5.8. The intention
570 was to use *glob{IO} instead, for which *glob{FILEHANDLE} is an alias.
571 However, this feature was undeprecated in Perl 5.24.
573 Calling POSIX::%s() is deprecated
575 The following functions in the "POSIX" module are no longer available:
577 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower",
578 "isprint", "ispunct", "isspace", "isupper", and "isxdigit". The
579 functions are buggy and don't work on UTF-8 encoded strings. See their
580 entries in POSIX for more information.
581 The functions were deprecated in Perl 5.20, and removed in Perl 5.24.
583 Perl 5.16
585 Use of %s on a handle without * is deprecated
586 It used to be possible to use "tie", "tied" or "untie" on a scalar
588 while the scalar holds a typeglob. This caused its filehandle to be
589 tied. It left no way to tie the scalar itself when it held a typeglob,
590 and no way to untie a scalar that had had a typeglob assigned to it.
591 This was deprecated in Perl 5.14, and the bug was fixed in Perl 5.16.
593 So now "tie $scalar" will always tie the scalar, not the handle it
595 holds. To tie the handle, use "tie *$scalar" (with an explicit
596 asterisk). The same applies to "tied *$scalar" and "untie *$scalar".
597
599 warnings, diagnostics.
600perl v5.38.2 2023-11-30 PERLDEPRECATION(1)