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 Perl 5.30
56 $* is no longer supported
57 Before Perl 5.10, setting $* to a true value globally enabled multi-
59 line matching within a string. This relique from the past lost its
60 special meaning in 5.10. Use of this variable will be a fatal error in
61 Perl 5.30, freeing the variable up for a future special meaning.
62 To enable multiline matching one should use the "/m" regexp modifier
64 (possibly in combination with "/s"). This can be set on a per match
65 bases, or can be enabled per lexical scope (including a whole file)
66 with "use re '/m'".
67 $# is no longer supported
69 This variable used to have a special meaning -- it could be used to
71 control how numbers were formatted when printed. This seldom used
72 functionality was removed in Perl 5.10. In order to free up the
73 variable for a future special meaning, its use will be a fatal error in
74 Perl 5.30.
75 To specify how numbers are formatted when printed, one is adviced to
77 use "printf" or "sprintf" instead.
78 "File::Glob::glob()" will disappear
80 "File::Glob" has a function called "glob", which just calls "bsd_glob".
82 However, its prototype is different from the prototype of "CORE::glob",
83 and hence, "File::Glob::glob" should not be used.
84 "File::Glob::glob()" was deprecated in Perl 5.8. A deprecation message
86 was issued from Perl 5.26 onwards, and the function will disappear in
87 Perl 5.30.
88 Code using "File::Glob::glob()" should call "File::Glob::bsd_glob()"
90 instead.
91 Unescaped left braces in regular expressions
93 The simple rule to remember, if you want to match a literal "{"
95 character (U+007B "LEFT CURLY BRACKET") in a regular expression
96 pattern, is to escape each literal instance of it in some way.
97 Generally easiest is to precede it with a backslash, like "\{" or
98 enclose it in square brackets ("[{]"). If the pattern delimiters are
99 also braces, any matching right brace ("}") should also be escaped to
100 avoid confusing the parser, for example,
101 qr{abc\{def\}ghi}
103 Forcing literal "{" characters to be escaped will enable the Perl
105 language to be extended in various ways in future releases. To avoid
106 needlessly breaking existing code, the restriction is is not enforced
107 in contexts where there are unlikely to ever be extensions that could
108 conflict with the use there of "{" as a literal.
109 Literal uses of "{" were deprecated in Perl 5.20, and some uses of it
111 started to give deprecation warnings since. These cases were made fatal
112 in Perl 5.26. Due to an oversight, not all cases of a use of a literal
113 "{" got a deprecation warning. These cases started warning in Perl
114 5.26, and they will be fatal by Perl 5.30.
115 Unqualified "dump()"
117 Use of "dump()" instead of "CORE::dump()" was deprecated in Perl 5.8,
119 and an unqualified "dump()" will no longer be available in Perl 5.30.
120 See "dump" in perlfunc.
122 Using my() in false conditional.
124 There has been a long-standing bug in Perl that causes a lexical
126 variable not to be cleared at scope exit when its declaration includes
127 a false conditional. Some people have exploited this bug to achieve a
128 kind of static variable. Since we intend to fix this bug, we don't
129 want people relying on this behavior.
130 Instead, it's recommended one uses "state" variables to achieve the
132 same effect:
133 use 5.10.0;
135 sub count {state $counter; return ++ $counter}
136 say count (); # Prints 1
137 say count (); # Prints 2
138 "state" variables were introduced in Perl 5.10.
140 Alternatively, you can achieve a similar static effect by declaring the
142 variable in a separate block outside the function, eg
143 sub f { my $x if 0; return $x++ }
145 becomes
147 { my $x; sub f { return $x++ } }
149 The use of "my()" in a false conditional has been deprecated in Perl
151 5.10, and it will become a fatal error in Perl 5.30.
152 Reading/writing bytes from/to :utf8 handles.
154 The sysread(), recv(), syswrite() and send() operators are deprecated
156 on handles that have the ":utf8" layer, either explicitly, or
157 implicitly, eg., with the ":encoding(UTF-16LE)" layer.
158 Both sysread() and recv() currently use only the ":utf8" flag for the
160 stream, ignoring the actual layers. Since sysread() and recv() do no
161 UTF-8 validation they can end up creating invalidly encoded scalars.
162 Similarly, syswrite() and send() use only the ":utf8" flag, otherwise
164 ignoring any layers. If the flag is set, both write the value UTF-8
165 encoded, even if the layer is some different encoding, such as the
166 example above.
167 Ideally, all of these operators would completely ignore the ":utf8"
169 state, working only with bytes, but this would result in silently
170 breaking existing code. To avoid this a future version of perl will
171 throw an exception when any of sysread(), recv(), syswrite() or send()
172 are called on handle with the ":utf8" layer.
173 In Perl 5.30, it will no longer be possible to use sysread(), recv(),
175 syswrite() or send() to read or send bytes from/to :utf8 handles.
176 Use of unassigned code point or non-standalone grapheme for a
178 delimiter.
179 A grapheme is what appears to a native-speaker of a language to be a
181 character. In Unicode (and hence Perl) a grapheme may actually be
182 several adjacent characters that together form a complete grapheme.
183 For example, there can be a base character, like "R" and an accent,
184 like a circumflex "^", that appear when displayed to be a single
185 character with the circumflex hovering over the "R". Perl currently
186 allows things like that circumflex to be delimiters of strings,
187 patterns, etc. When displayed, the circumflex would look like it
188 belongs to the character just to the left of it. In order to move the
189 language to be able to accept graphemes as delimiters, we have to
190 deprecate the use of delimiters which aren't graphemes by themselves.
191 Also, a delimiter must already be assigned (or known to be never going
192 to be assigned) to try to future-proof code, for otherwise code that
193 works today would fail to compile if the currently unassigned delimiter
194 ends up being something that isn't a stand-alone grapheme. Because
195 Unicode is never going to assign non-character code points, nor code
196 points that are above the legal Unicode maximum, those can be
197 delimiters, and their use won't raise this warning.
198 In Perl 5.30, delimiters which are unassigned code points, or which are
200 non-standalone graphemes will be fatal.
201 In XS code, use of various macros dealing with UTF-8.
203 These macros will require an extra parameter in Perl 5.30:
205 "isALPHANUMERIC_utf8", "isASCII_utf8", "isBLANK_utf8", "isCNTRL_utf8",
206 "isDIGIT_utf8", "isIDFIRST_utf8", "isPSXSPC_utf8", "isSPACE_utf8",
207 "isVERTWS_utf8", "isWORDCHAR_utf8", "isXDIGIT_utf8",
208 "isALPHANUMERIC_LC_utf8", "isALPHA_LC_utf8", "isASCII_LC_utf8",
209 "isBLANK_LC_utf8", "isCNTRL_LC_utf8", "isDIGIT_LC_utf8",
210 "isGRAPH_LC_utf8", "isIDCONT_LC_utf8", "isIDFIRST_LC_utf8",
211 "isLOWER_LC_utf8", "isPRINT_LC_utf8", "isPSXSPC_LC_utf8",
212 "isPUNCT_LC_utf8", "isSPACE_LC_utf8", "isUPPER_LC_utf8",
213 "isWORDCHAR_LC_utf8", "isXDIGIT_LC_utf8", "toFOLD_utf8",
214 "toLOWER_utf8", "toTITLE_utf8", and "toUPPER_utf8".
215 There is now a macro that corresponds to each one of these, simply by
217 appending "_safe" to the name. It takes the extra parameter. For
218 example, "isDIGIT_utf8_safe" corresponds to "isDIGIT_utf8", but takes
219 the extra parameter, and its use doesn't generate a deprecation
220 warning. All are documented in "Character case changing" in perlapi
221 and "Character classification" in perlapi.
222 You can change to use these versions at any time, or, if you can live
224 with the deprecation messages, wait until 5.30 and add the parameter to
225 the existing calls, without changing the names.
226 Perl 5.28
228 Attribute "%s" is deprecated, and will disappear in 5.28
229 The attributes ":locked" (on code references) and ":unique" (on array,
231 hash and scalar references) have had no effect since Perl 5.005 and
232 Perl 5.8.8 respectively. Their use has been deprecated since.
233 These attributes will no longer be recognized in Perl 5.28, and will
235 then result in a syntax error. Since the attributes do not do anything,
236 removing them from your code fixes the deprecation warning; and
237 removing them will not influence the behaviour of your code.
238 Bare here-document terminators
240 Perl has allowed you to use a bare here-document terminator to have the
242 here-document end at the first empty line. This practise was deprecated
243 in Perl 5.000, and this will be a fatal error in Perl 5.28.
244 You are encouraged to use the explictly quoted form if you wish to use
246 an empty line as the terminator of the here-document:
247 print <<"";
249 Print this line.
250 # Previous blank line ends the here-document.
252 Setting $/ to a reference to a non-positive integer
254 You assigned a reference to a scalar to $/ where the referenced item is
256 not a positive integer. In older perls this appeared to work the same
257 as setting it to "undef" but was in fact internally different, less
258 efficient and with very bad luck could have resulted in your file being
259 split by a stringified form of the reference.
260 In Perl 5.20.0 this was changed so that it would be exactly the same as
262 setting $/ to undef, with the exception that this warning would be
263 thrown.
264 In Perl 5.28, this will throw a fatal error.
266 You are recommended to change your code to set $/ to "undef" explicitly
268 if you wish to slurp the file.
269 Limit on the value of Unicode code points.
271 Unicode only allows code points up to 0x10FFFF, but Perl allows much
273 larger ones. However, using code points exceeding the maximum value of
274 an integer ("IV_MAX") may break the perl interpreter in some
275 constructs, including causing it to hang in a few cases. The known
276 problem areas are in "tr///", regular expression pattern matching using
277 quantifiers, as quote delimiters in "qX...X" (where X is the "chr()" of
278 a large code point), and as the upper limits in loops.
279 The use of out of range code points was deprecated in Perl 5.24, and it
281 will be a fatal error in Perl 5.28.
282 If your code is to run on various platforms, keep in mind that the
284 upper limit depends on the platform. It is much larger on 64-bit word
285 sizes than 32-bit ones.
286 Use of comma-less variable list in formats.
288 It's allowed to use a list of variables in a format, without separating
290 them with commas. This usage has been deprecated for a long time, and
291 it will be a fatal error in Perl 5.28.
292 Use of "\N{}"
294 Use of "\N{}" with nothing between the braces was deprecated in Perl
296 5.24, and will throw a fatal error in Perl 5.28.
297 Since such a construct is equivalent to using an empty string, you are
299 recommended to remove such "\N{}" constructs.
300 Using the same symbol to open a filehandle and a dirhandle
302 It used to be legal to use "open()" to associate both a filehandle and
304 a dirhandle to the same symbol (glob or scalar). This idiom is likely
305 to be confusing, and it was deprecated in Perl 5.10.
306 Using the same symbol to "open()" a filehandle and a dirhandle will be
308 a fatal error in Perl 5.28.
309 You should be using two different symbols instead.
311 ${^ENCODING} is no longer supported.
313 The special variable "${^ENCODING}" was used to implement the
315 "encoding" pragma. Setting this variable to anything other than "undef"
316 was deprecated in Perl 5.22. Full deprecation of the variable happened
317 in Perl 5.25.3.
318 Setting this variable will become a fatal error in Perl 5.28.
320 "B::OP::terse"
322 This method, which just calls "B::Concise::b_terse", has been
324 deprecated, and will disappear in Perl 5.28. Please use "B::Concise"
325 instead.
326 Use of inherited AUTOLOAD for non-method %s() is deprecated
328 As an (ahem) accidental feature, "AUTOLOAD" subroutines are looked up
330 as methods (using the @ISA hierarchy) even when the subroutines to be
331 autoloaded were called as plain functions (e.g. "Foo::bar()"), not as
332 methods (e.g. "Foo->bar()" or "$obj->bar()").
333 This bug will be rectified in future by using method lookup only for
335 methods' "AUTOLOAD"s.
336 The simple rule is: Inheritance will not work when autoloading non-
338 methods. The simple fix for old code is: In any module that used to
339 depend on inheriting "AUTOLOAD" for non-methods from a base class named
340 "BaseClass", execute "*AUTOLOAD = \&BaseClass::AUTOLOAD" during
341 startup.
342 In code that currently says "use AutoLoader; @ISA = qw(AutoLoader);"
344 you should remove AutoLoader from @ISA and change "use AutoLoader;" to
345 "use AutoLoader 'AUTOLOAD';".
346 This feature was deprecated in Perl 5.004, and will be fatal in Perl
348 5.28.
349 Use of code points over 0xFF in string bitwise operators
351 The string bitwise operators, "&", "|", "^", and "~", treat their
353 operands as strings of bytes. As such, values above 0xFF are
354 nonsensical. Using such code points with these operators was deprecated
355 in Perl 5.24, and will be fatal in Perl 5.28.
356 In XS code, use of "to_utf8_case()"
358 This function is being removed; instead convert to call the appropriate
360 one of: "toFOLD_utf8_safe". "toLOWER_utf8_safe", "toTITLE_utf8_safe",
361 or "toUPPER_utf8_safe".
362 Perl 5.26
364 "--libpods" in "Pod::Html"
365 Since Perl 5.18, the option "--libpods" has been deprecated, and using
367 this option did not do anything other than producing a warning.
368 The "--libpods" option is no longer recognized in Perl 5.26.
370 The utilities "c2ph" and "pstruct"
372 These old, perl3-era utilities have been deprecated in favour of "h2xs"
374 for a long time. In Perl 5.26, they have been removed.
375 Trapping "$SIG {__DIE__}" other than during program exit.
377 The $SIG{__DIE__} hook is called even inside an "eval()". It was never
379 intended to happen this way, but an implementation glitch made this
380 possible. This used to be deprecated, as it allowed strange action at a
381 distance like rewriting a pending exception in $@. Plans to rectify
382 this have been scrapped, as users found that rewriting a pending
383 exception is actually a useful feature, and not a bug.
384 Perl never issued a deprecation warning for this; the deprecation was
386 by documentation policy only. But this deprecation has been lifted in
387 Perl 5.26.
388 Malformed UTF-8 string in "%s"
390 This message indicates a bug either in the Perl core or in XS code.
392 Such code was trying to find out if a character, allegedly stored
393 internally encoded as UTF-8, was of a given type, such as being
394 punctuation or a digit. But the character was not encoded in legal
395 UTF-8. The %s is replaced by a string that can be used by
396 knowledgeable people to determine what the type being checked against
397 was.
398 Passing malformed strings was deprecated in Perl 5.18, and became fatal
400 in Perl 5.26.
401 Perl 5.24
403 Use of *glob{FILEHANDLE}
404 The use of *glob{FILEHANDLE} was deprecated in Perl 5.8. The intention
406 was to use *glob{IO} instead, for which *glob{FILEHANDLE} is an alias.
407 However, this feature was undeprecated in Perl 5.24.
409 Calling POSIX::%s() is deprecated
411 The following functions in the "POSIX" module are no longer available:
413 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower",
414 "isprint", "ispunct", "isspace", "isupper", and "isxdigit". The
415 functions are buggy and don't work on UTF-8 encoded strings. See their
416 entries in POSIX for more information.
417 The functions were deprecated in Perl 5.20, and removed in Perl 5.24.
419 Perl 5.16
421 Use of %s on a handle without * is deprecated
422 It used to be possible to use "tie", "tied" or "untie" on a scalar
424 while the scalar holds a typeglob. This caused its filehandle to be
425 tied. It left no way to tie the scalar itself when it held a typeglob,
426 and no way to untie a scalar that had had a typeglob assigned to it.
427 This was deprecated in Perl 5.14, and the bug was fixed in Perl 5.16.
429 So now "tie $scalar" will always tie the scalar, not the handle it
431 holds. To tie the handle, use "tie *$scalar" (with an explicit
432 asterisk). The same applies to "tied *$scalar" and "untie *$scalar".
433
435 warnings, diagnostics.
436perl v5.26.3 2018-03-23 PERLDEPRECATION(1)