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 Perl 5.32
20 Constants from lexical variables potentially modified elsewhere
21 You wrote something like
23 my $var;
25 $sub = sub () { $var };
26 but $var is referenced elsewhere and could be modified after the "sub"
28 expression is evaluated. Either it is explicitly modified elsewhere
29 ("$var = 3") or it is passed to a subroutine or to an operator like
30 "printf" or "map", which may or may not modify the variable.
31 Traditionally, Perl has captured the value of the variable at that
33 point and turned the subroutine into a constant eligible for inlining.
34 In those cases where the variable can be modified elsewhere, this
35 breaks the behavior of closures, in which the subroutine captures the
36 variable itself, rather than its value, so future changes to the
37 variable are reflected in the subroutine's return value.
38 If you intended for the subroutine to be eligible for inlining, then
40 make sure the variable is not referenced elsewhere, possibly by copying
41 it:
42 my $var2 = $var;
44 $sub = sub () { $var2 };
45 If you do want this subroutine to be a closure that reflects future
47 changes to the variable that it closes over, add an explicit "return":
48 my $var;
50 $sub = sub () { return $var };
51 This usage has been deprecated, and will no longer be allowed in Perl
53 5.32.
54 Use of strings with code points over 0xFF as arguments to "vec"
56 "vec" views its string argument as a sequence of bits. A string
58 containing a code point over 0xFF is nonsensical. This usage is
59 deprecated in Perl 5.28, and will be removed in Perl 5.32.
60 Use of code points over 0xFF in string bitwise operators
62 The string bitwise operators, "&", "|", "^", and "~", treat their
64 operands as strings of bytes. As such, values above 0xFF are
65 nonsensical. Some instances of these have been deprecated since Perl
66 5.24, and were made fatal in 5.28, but it turns out that in cases where
67 the wide characters did not affect the end result, no deprecation
68 notice was raised, and so remain legal. Now, all occurrences either
69 are fatal or raise a deprecation warning, so that the remaining legal
70 occurrences will be fatal in 5.32.
71 An example of this is
73 "" & "\x{100}"
75 The wide character is not used in the "&" operation because the left
77 operand is shorter. This now warns anyway.
78 hostname() doesn't accept any arguments
80 The function "hostname()" in the Sys::Hostname module has always been
82 documented to be called with no arguments. Historically it has not
83 enforced this, and has actually accepted and ignored any arguments. As
84 a result, some users have got the mistaken impression that an argument
85 does something useful. To avoid these bugs, the function is being made
86 strict. Passing arguments was deprecated in Perl 5.28, and will become
87 fatal in Perl 5.32.
88 Unescaped left braces in regular expressions
90 The simple rule to remember, if you want to match a literal "{"
92 character (U+007B "LEFT CURLY BRACKET") in a regular expression
93 pattern, is to escape each literal instance of it in some way.
94 Generally easiest is to precede it with a backslash, like "\{" or
95 enclose it in square brackets ("[{]"). If the pattern delimiters are
96 also braces, any matching right brace ("}") should also be escaped to
97 avoid confusing the parser, for example,
98 qr{abc\{def\}ghi}
100 Forcing literal "{" characters to be escaped will enable the Perl
102 language to be extended in various ways in future releases. To avoid
103 needlessly breaking existing code, the restriction is is not enforced
104 in contexts where there are unlikely to ever be extensions that could
105 conflict with the use there of "{" as a literal.
106 Literal uses of "{" were deprecated in Perl 5.20, and some uses of it
108 started to give deprecation warnings since. These cases were made fatal
109 in Perl 5.26. Due to an oversight, not all cases of a use of a literal
110 "{" got a deprecation warning. Some cases started warning in Perl
111 5.26, and they will be fatal by Perl 5.30. Other case started in Perl
112 5.28, and will be made fatal in 5.32.
113 Perl 5.30
115 $* is no longer supported
116 Before Perl 5.10, setting $* to a true value globally enabled multi-
118 line matching within a string. This relique from the past lost its
119 special meaning in 5.10. Use of this variable will be a fatal error in
120 Perl 5.30, freeing the variable up for a future special meaning.
121 To enable multiline matching one should use the "/m" regexp modifier
123 (possibly in combination with "/s"). This can be set on a per match
124 bases, or can be enabled per lexical scope (including a whole file)
125 with "use re '/m'".
126 $# is no longer supported
128 This variable used to have a special meaning -- it could be used to
130 control how numbers were formatted when printed. This seldom used
131 functionality was removed in Perl 5.10. In order to free up the
132 variable for a future special meaning, its use will be a fatal error in
133 Perl 5.30.
134 To specify how numbers are formatted when printed, one is advised to
136 use "printf" or "sprintf" instead.
137 Assigning non-zero to $[ will be fatal
139 This variable (and the corresponding "array_base" feature and arybase
141 module) allows changing the base for array and string indexing
142 operations.
143 Setting this to a non-zero value has been deprecated since Perl 5.12
145 and will become fatal in Perl 5.30.
146 "File::Glob::glob()" will disappear
148 "File::Glob" has a function called "glob", which just calls "bsd_glob".
150 However, its prototype is different from the prototype of "CORE::glob",
151 and hence, "File::Glob::glob" should not be used.
152 "File::Glob::glob()" was deprecated in Perl 5.8. A deprecation message
154 was issued from Perl 5.26 onwards, and the function will disappear in
155 Perl 5.30.
156 Code using "File::Glob::glob()" should call "File::Glob::bsd_glob()"
158 instead.
159 Unescaped left braces in regular expressions (for 5.30)
161 See "Unescaped left braces in regular expressions" above.
163 Unqualified "dump()"
165 Use of "dump()" instead of "CORE::dump()" was deprecated in Perl 5.8,
167 and an unqualified "dump()" will no longer be available in Perl 5.30.
168 See "dump" in perlfunc.
170 Using my() in false conditional.
172 There has been a long-standing bug in Perl that causes a lexical
174 variable not to be cleared at scope exit when its declaration includes
175 a false conditional. Some people have exploited this bug to achieve a
176 kind of static variable. Since we intend to fix this bug, we don't
177 want people relying on this behavior.
178 Instead, it's recommended one uses "state" variables to achieve the
180 same effect:
181 use 5.10.0;
183 sub count {state $counter; return ++ $counter}
184 say count (); # Prints 1
185 say count (); # Prints 2
186 "state" variables were introduced in Perl 5.10.
188 Alternatively, you can achieve a similar static effect by declaring the
190 variable in a separate block outside the function, eg
191 sub f { my $x if 0; return $x++ }
193 becomes
195 { my $x; sub f { return $x++ } }
197 The use of "my()" in a false conditional has been deprecated in Perl
199 5.10, and it will become a fatal error in Perl 5.30.
200 Reading/writing bytes from/to :utf8 handles.
202 The sysread(), recv(), syswrite() and send() operators are deprecated
204 on handles that have the ":utf8" layer, either explicitly, or
205 implicitly, eg., with the ":encoding(UTF-16LE)" layer.
206 Both sysread() and recv() currently use only the ":utf8" flag for the
208 stream, ignoring the actual layers. Since sysread() and recv() do no
209 UTF-8 validation they can end up creating invalidly encoded scalars.
210 Similarly, syswrite() and send() use only the ":utf8" flag, otherwise
212 ignoring any layers. If the flag is set, both write the value UTF-8
213 encoded, even if the layer is some different encoding, such as the
214 example above.
215 Ideally, all of these operators would completely ignore the ":utf8"
217 state, working only with bytes, but this would result in silently
218 breaking existing code. To avoid this a future version of perl will
219 throw an exception when any of sysread(), recv(), syswrite() or send()
220 are called on handle with the ":utf8" layer.
221 In Perl 5.30, it will no longer be possible to use sysread(), recv(),
223 syswrite() or send() to read or send bytes from/to :utf8 handles.
224 Use of unassigned code point or non-standalone grapheme for a
226 delimiter.
227 A grapheme is what appears to a native-speaker of a language to be a
229 character. In Unicode (and hence Perl) a grapheme may actually be
230 several adjacent characters that together form a complete grapheme.
231 For example, there can be a base character, like "R" and an accent,
232 like a circumflex "^", that appear when displayed to be a single
233 character with the circumflex hovering over the "R". Perl currently
234 allows things like that circumflex to be delimiters of strings,
235 patterns, etc. When displayed, the circumflex would look like it
236 belongs to the character just to the left of it. In order to move the
237 language to be able to accept graphemes as delimiters, we have to
238 deprecate the use of delimiters which aren't graphemes by themselves.
239 Also, a delimiter must already be assigned (or known to be never going
240 to be assigned) to try to future-proof code, for otherwise code that
241 works today would fail to compile if the currently unassigned delimiter
242 ends up being something that isn't a stand-alone grapheme. Because
243 Unicode is never going to assign non-character code points, nor code
244 points that are above the legal Unicode maximum, those can be
245 delimiters, and their use won't raise this warning.
246 In Perl 5.30, delimiters which are unassigned code points, or which are
248 non-standalone graphemes will be fatal.
249 In XS code, use of various macros dealing with UTF-8.
251 These macros will require an extra parameter in Perl 5.30:
253 "isALPHANUMERIC_utf8", "isASCII_utf8", "isBLANK_utf8", "isCNTRL_utf8",
254 "isDIGIT_utf8", "isIDFIRST_utf8", "isPSXSPC_utf8", "isSPACE_utf8",
255 "isVERTWS_utf8", "isWORDCHAR_utf8", "isXDIGIT_utf8",
256 "isALPHANUMERIC_LC_utf8", "isALPHA_LC_utf8", "isASCII_LC_utf8",
257 "isBLANK_LC_utf8", "isCNTRL_LC_utf8", "isDIGIT_LC_utf8",
258 "isGRAPH_LC_utf8", "isIDCONT_LC_utf8", "isIDFIRST_LC_utf8",
259 "isLOWER_LC_utf8", "isPRINT_LC_utf8", "isPSXSPC_LC_utf8",
260 "isPUNCT_LC_utf8", "isSPACE_LC_utf8", "isUPPER_LC_utf8",
261 "isWORDCHAR_LC_utf8", "isXDIGIT_LC_utf8", "toFOLD_utf8",
262 "toLOWER_utf8", "toTITLE_utf8", and "toUPPER_utf8".
263 There is now a macro that corresponds to each one of these, simply by
265 appending "_safe" to the name. It takes the extra parameter. For
266 example, "isDIGIT_utf8_safe" corresponds to "isDIGIT_utf8", but takes
267 the extra parameter, and its use doesn't generate a deprecation
268 warning. All are documented in "Character case changing" in perlapi
269 and "Character classification" in perlapi.
270 You can change to use these versions at any time, or, if you can live
272 with the deprecation messages, wait until 5.30 and add the parameter to
273 the existing calls, without changing the names.
274 Perl 5.28
276 Attributes ":locked" and ":unique"
277 The attributes ":locked" (on code references) and ":unique" (on array,
279 hash and scalar references) have had no effect since Perl 5.005 and
280 Perl 5.8.8 respectively. Their use has been deprecated since.
281 As of Perl 5.28, these attributes are syntax errors. Since the
283 attributes do not do anything, removing them from your code fixes the
284 syntax error; and removing them will not influence the behaviour of
285 your code.
286 Bare here-document terminators
288 Perl has allowed you to use a bare here-document terminator to have the
290 here-document end at the first empty line. This practise was deprecated
291 in Perl 5.000; as of Perl 5.28, using a bare here-document terminator
292 throws a fatal error.
293 You are encouraged to use the explicitly quoted form if you wish to use
295 an empty line as the terminator of the here-document:
296 print <<"";
298 Print this line.
299 # Previous blank line ends the here-document.
301 Setting $/ to a reference to a non-positive integer
303 You assigned a reference to a scalar to $/ where the referenced item is
305 not a positive integer. In older perls this appeared to work the same
306 as setting it to "undef" but was in fact internally different, less
307 efficient and with very bad luck could have resulted in your file being
308 split by a stringified form of the reference.
309 In Perl 5.20.0 this was changed so that it would be exactly the same as
311 setting $/ to undef, with the exception that this warning would be
312 thrown.
313 As of Perl 5.28, setting $/ to a reference of a non-positive integer
315 throws a fatal error.
316 You are recommended to change your code to set $/ to "undef" explicitly
318 if you wish to slurp the file.
319 Limit on the value of Unicode code points.
321 Unicode only allows code points up to 0x10FFFF, but Perl allows much
323 larger ones. Up till Perl 5.28, it was allowed to use code points
324 exceeding the maximum value of an integer ("IV_MAX"). However, that
325 did break the perl interpreter in some constructs, including causing it
326 to hang in a few cases. The known problem areas were in "tr///",
327 regular expression pattern matching using quantifiers, as quote
328 delimiters in "qX...X" (where X is the "chr()" of a large code point),
329 and as the upper limits in loops.
330 The use of out of range code points was deprecated in Perl 5.24; as of
332 Perl 5.28 using a code point exceeding "IV_MAX" throws a fatal error.
333 If your code is to run on various platforms, keep in mind that the
335 upper limit depends on the platform. It is much larger on 64-bit word
336 sizes than 32-bit ones. For 32-bit integers, "IV_MAX" equals
337 0x7FFFFFFF, for 64-bit integers, "IV_MAX" equals 0x7FFFFFFFFFFFFFFF.
338 Use of comma-less variable list in formats.
340 It was allowed to use a list of variables in a format, without
342 separating them with commas. This usage has been deprecated for a long
343 time, and as of Perl 5.28, this throws a fatal error.
344 Use of "\N{}"
346 Use of "\N{}" with nothing between the braces was deprecated in Perl
348 5.24, and throws a fatal error as of Perl 5.28.
349 Since such a construct is equivalent to using an empty string, you are
351 recommended to remove such "\N{}" constructs.
352 Using the same symbol to open a filehandle and a dirhandle
354 It used to be legal to use "open()" to associate both a filehandle and
356 a dirhandle to the same symbol (glob or scalar). This idiom is likely
357 to be confusing, and it was deprecated in Perl 5.10.
358 Using the same symbol to "open()" a filehandle and a dirhandle throws a
360 fatal error as of Perl 5.28.
361 You should be using two different symbols instead.
363 ${^ENCODING} is no longer supported.
365 The special variable "${^ENCODING}" was used to implement the
367 "encoding" pragma. Setting this variable to anything other than "undef"
368 was deprecated in Perl 5.22. Full deprecation of the variable happened
369 in Perl 5.25.3.
370 Setting this variable to anything other than an undefined value throws
372 a fatal error as of Perl 5.28.
373 "B::OP::terse"
375 This method, which just calls "B::Concise::b_terse", has been
377 deprecated, and disappeared in Perl 5.28. Please use "B::Concise"
378 instead.
379 Use of inherited AUTOLOAD for non-method %s::%s() is no longer allowed
381 As an (ahem) accidental feature, "AUTOLOAD" subroutines were looked up
383 as methods (using the @ISA hierarchy) even when the subroutines to be
384 autoloaded were called as plain functions (e.g. "Foo::bar()"), not as
385 methods (e.g. "Foo->bar()" or "$obj->bar()").
386 This bug was deprecated in Perl 5.004, has been rectified in Perl 5.28
388 by using method lookup only for methods' "AUTOLOAD"s.
389 The simple rule is: Inheritance will not work when autoloading non-
391 methods. The simple fix for old code is: In any module that used to
392 depend on inheriting "AUTOLOAD" for non-methods from a base class named
393 "BaseClass", execute "*AUTOLOAD = \&BaseClass::AUTOLOAD" during
394 startup.
395 In code that currently says "use AutoLoader; @ISA = qw(AutoLoader);"
397 you should remove AutoLoader from @ISA and change "use AutoLoader;" to
398 "use AutoLoader 'AUTOLOAD';".
399 Use of code points over 0xFF in string bitwise operators
401 The string bitwise operators, "&", "|", "^", and "~", treat their
403 operands as strings of bytes. As such, values above 0xFF are
404 nonsensical. Using such code points with these operators was deprecated
405 in Perl 5.24, and is fatal as of Perl 5.28.
406 In XS code, use of "to_utf8_case()"
408 This function has been removed as of Perl 5.28; instead convert to call
410 the appropriate one of: "toFOLD_utf8_safe". "toLOWER_utf8_safe",
411 "toTITLE_utf8_safe", or "toUPPER_utf8_safe".
412 Perl 5.26
414 "--libpods" in "Pod::Html"
415 Since Perl 5.18, the option "--libpods" has been deprecated, and using
417 this option did not do anything other than producing a warning.
418 The "--libpods" option is no longer recognized as of Perl 5.26.
420 The utilities "c2ph" and "pstruct"
422 These old, perl3-era utilities have been deprecated in favour of "h2xs"
424 for a long time. As of Perl 5.26, they have been removed.
425 Trapping "$SIG {__DIE__}" other than during program exit.
427 The $SIG{__DIE__} hook is called even inside an "eval()". It was never
429 intended to happen this way, but an implementation glitch made this
430 possible. This used to be deprecated, as it allowed strange action at a
431 distance like rewriting a pending exception in $@. Plans to rectify
432 this have been scrapped, as users found that rewriting a pending
433 exception is actually a useful feature, and not a bug.
434 Perl never issued a deprecation warning for this; the deprecation was
436 by documentation policy only. But this deprecation has been lifted as
437 of Perl 5.26.
438 Malformed UTF-8 string in "%s"
440 This message indicates a bug either in the Perl core or in XS code.
442 Such code was trying to find out if a character, allegedly stored
443 internally encoded as UTF-8, was of a given type, such as being
444 punctuation or a digit. But the character was not encoded in legal
445 UTF-8. The %s is replaced by a string that can be used by
446 knowledgeable people to determine what the type being checked against
447 was.
448 Passing malformed strings was deprecated in Perl 5.18, and became fatal
450 in Perl 5.26.
451 Perl 5.24
453 Use of *glob{FILEHANDLE}
454 The use of *glob{FILEHANDLE} was deprecated in Perl 5.8. The intention
456 was to use *glob{IO} instead, for which *glob{FILEHANDLE} is an alias.
457 However, this feature was undeprecated in Perl 5.24.
459 Calling POSIX::%s() is deprecated
461 The following functions in the "POSIX" module are no longer available:
463 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower",
464 "isprint", "ispunct", "isspace", "isupper", and "isxdigit". The
465 functions are buggy and don't work on UTF-8 encoded strings. See their
466 entries in POSIX for more information.
467 The functions were deprecated in Perl 5.20, and removed in Perl 5.24.
469 Perl 5.16
471 Use of %s on a handle without * is deprecated
472 It used to be possible to use "tie", "tied" or "untie" on a scalar
474 while the scalar holds a typeglob. This caused its filehandle to be
475 tied. It left no way to tie the scalar itself when it held a typeglob,
476 and no way to untie a scalar that had had a typeglob assigned to it.
477 This was deprecated in Perl 5.14, and the bug was fixed in Perl 5.16.
479 So now "tie $scalar" will always tie the scalar, not the handle it
481 holds. To tie the handle, use "tie *$scalar" (with an explicit
482 asterisk). The same applies to "tied *$scalar" and "untie *$scalar".
483
485 warnings, diagnostics.
486perl v5.28.2 2018-11-01 PERLDEPRECATION(1)