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perldelta: remove placeholders for module changes
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1=encoding utf8
2
3=head1 NAME
4
5ed58cbd 5perldelta - what is new for perl v5.18.0
e128ab2c 6
4eabcf70 7=head1 DESCRIPTION
6db9054f 8
e612b5a0 9This document describes differences between the v5.16.0 release and the v5.18.0
e08634c5 10release.
6db9054f 11
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12If you are upgrading from an earlier release such as v5.14.0, first read
13L<perl5160delta>, which describes differences between v5.14.0 and v5.16.0.
3f01b192 14
5ed58cbd 15=head1 Core Enhancements
3f01b192 16
5ed58cbd 17=head2 New mechanism for experimental features
82d98f72 18
5ed58cbd 19Newly-added experimental features will now require this incantation:
82d98f72 20
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21 no warnings "experimental::feature_name";
22 use feature "feature_name"; # would warn without the prev line
23
24There is a new warnings category, called "experimental", containing
25warnings that the L<feature> pragma emits when enabling experimental
26features.
27
28Newly-added experimental features will also be given special warning IDs,
29which consist of "experimental::" followed by the name of the feature. (The
30plan is to extend this mechanism eventually to all warnings, to allow them
31to be enabled or disabled individually, and not just by category.)
32
33By saying
34
35 no warnings "experimental::feature_name";
36
37you are taking responsibility for any breakage that future changes to, or
38removal of, the feature may cause.
39
40Existing experimental features may begin emitting these warnings, too. Please
41consult L<perlexperiment> for information on which features are considered
42experimental.
43
44=head2 Hash overhaul
45
e612b5a0 46Changes to the implementation of hashes in perl v5.18.0 will be one of the most
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47visible changes to the behavior of existing code.
48
8e74b2ed 49By default, two distinct hash variables with identical keys and values may now
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50provide their contents in a different order where it was previously identical.
51
52When encountering these changes, the key to cleaning up from them is to accept
53that B<hashes are unordered collections> and to act accordingly.
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54
55=head3 Hash randomization
56
57The seed used by Perl's hash function is now random. This means that the
58order which keys/values will be returned from functions like C<keys()>,
59C<values()>, and C<each()> will differ from run to run.
60
61This change was introduced to make Perl's hashes more robust to algorithmic
62complexity attacks, and also because we discovered that it exposes hash
63ordering dependency bugs and makes them easier to track down.
64
65Toolchain maintainers might want to invest in additional infrastructure to
66test for things like this. Running tests several times in a row and then
67comparing results will make it easier to spot hash order dependencies in
68code. Authors are strongly encouraged not to expose the key order of
69Perl's hashes to insecure audiences.
70
71Further, every hash has its own iteration order, which should make it much
72more difficult to determine what the current hash seed is.
73
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74=head3 New hash functions
75
e612b5a0 76Perl v5.18 includes support for multiple hash functions, and changed
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77the default (to ONE_AT_A_TIME_HARD), you can choose a different
78algorithm by defining a symbol at compile time. For a current list,
e612b5a0 79consult the F<INSTALL> document. Note that as of Perl v5.18 we can
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80only recommend use of the default or SIPHASH. All the others are
81known to have security issues and are for research purposes only.
5ed58cbd 82
f105b7be 83=head3 PERL_HASH_SEED environment variable now takes a hex value
5ed58cbd 84
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85C<PERL_HASH_SEED> no longer accepts an integer as a parameter;
86instead the value is expected to be a binary value encoded in a hex
87string, such as "0xf5867c55039dc724". This is to make the
88infrastructure support hash seeds of arbitrary lengths, which might
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89exceed that of an integer. (SipHash uses a 16 byte seed).
90
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91=head3 PERL_PERTURB_KEYS environment variable added
92
f105b7be 93The C<PERL_PERTURB_KEYS> environment variable allows one to control the level of
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94randomization applied to C<keys> and friends.
95
f105b7be 96When C<PERL_PERTURB_KEYS> is 0, perl will not randomize the key order at all. The
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97chance that C<keys> changes due to an insert will be the same as in previous
98perls, basically only when the bucket size is changed.
99
f105b7be 100When C<PERL_PERTURB_KEYS> is 1, perl will randomize keys in a non-repeatable
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101way. The chance that C<keys> changes due to an insert will be very high. This
102is the most secure and default mode.
103
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104When C<PERL_PERTURB_KEYS> is 2, perl will randomize keys in a repeatable way.
105Repeated runs of the same program should produce the same output every time.
c40c48bb 106
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107C<PERL_HASH_SEED> implies a non-default C<PERL_PERTURB_KEYS> setting. Setting
108C<PERL_HASH_SEED=0> (exactly one 0) implies C<PERL_PERTURB_KEYS=0> (hash key
109randomization disabled); settng C<PERL_HASH_SEED> to any other value implies
110C<PERL_PERTURB_KEYS=2> (deterministic and repeatable hash key randomization).
111Specifying C<PERL_PERTURB_KEYS> explicitly to a different level overrides this
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112behavior.
113
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114=head3 Hash::Util::hash_seed() now returns a string
115
116Hash::Util::hash_seed() now returns a string instead of an integer. This
117is to make the infrastructure support hash seeds of arbitrary lengths
118which might exceed that of an integer. (SipHash uses a 16 byte seed).
119
120=head3 Output of PERL_HASH_SEED_DEBUG has been changed
121
122The environment variable PERL_HASH_SEED_DEBUG now makes perl show both the
f105b7be 123hash function perl was built with, I<and> the seed, in hex, in use for that
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124process. Code parsing this output, should it exist, must change to accommodate
125the new format. Example of the new format:
126
127 $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
128 HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f
129
130=head2 Upgrade to Unicode 6.2
131
2e7bc647 132Perl now supports Unicode 6.2. A list of changes from Unicode
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1336.1 is at L<http://www.unicode.org/versions/Unicode6.2.0>.
134
135=head2 Character name aliases may now include non-Latin1-range characters
136
137It is possible to define your own names for characters for use in
138C<\N{...}>, C<charnames::vianame()>, etc. These names can now be
139comprised of characters from the whole Unicode range. This allows for
140names to be in your native language, and not just English. Certain
141restrictions apply to the characters that may be used (you can't define
142a name that has punctuation in it, for example). See L<charnames/CUSTOM
143ALIASES>.
144
145=head2 New DTrace probes
146
147The following new DTrace probes have been added:
14731ad1 148
337fb649 149=over 4
14731ad1 150
82d98f72 151=item *
14731ad1 152
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153C<op-entry>
154
155=item *
156
157C<loading-file>
158
159=item *
160
161C<loaded-file>
162
163=back
164
165=head2 C<${^LAST_FH}>
166
167This new variable provides access to the filehandle that was last read.
168This is the handle used by C<$.> and by C<tell> and C<eof> without
169arguments.
170
171=head2 Regular Expression Set Operations
172
173This is an B<experimental> feature to allow matching against the union,
174intersection, etc., of sets of code points, similar to
175L<Unicode::Regex::Set>. It can also be used to extend C</x> processing
176to [bracketed] character classes, and as a replacement of user-defined
177properties, allowing more complex expressions than they do. See
178L<perlrecharclass/Extended Bracketed Character Classes>.
179
180=head2 Lexical subroutines
181
182This new feature is still considered B<experimental>. To enable it:
183
184 use 5.018;
185 no warnings "experimental::lexical_subs";
186 use feature "lexical_subs";
187
188You can now declare subroutines with C<state sub foo>, C<my sub foo>, and
189C<our sub foo>. (C<state sub> requires that the "state" feature be
190enabled, unless you write it as C<CORE::state sub foo>.)
191
192C<state sub> creates a subroutine visible within the lexical scope in which
193it is declared. The subroutine is shared between calls to the outer sub.
194
195C<my sub> declares a lexical subroutine that is created each time the
196enclosing block is entered. C<state sub> is generally slightly faster than
197C<my sub>.
198
199C<our sub> declares a lexical alias to the package subroutine of the same
200name.
201
202For more information, see L<perlsub/Lexical Subroutines>.
203
204=head2 Computed Labels
205
206The loop controls C<next>, C<last> and C<redo>, and the special C<dump>
207operator, now allow arbitrary expressions to be used to compute labels at run
208time. Previously, any argument that was not a constant was treated as the
209empty string.
210
211=head2 More CORE:: subs
212
213Several more built-in functions have been added as subroutines to the
214CORE:: namespace - namely, those non-overridable keywords that can be
215implemented without custom parsers: C<defined>, C<delete>, C<exists>,
216C<glob>, C<pos>, C<protoytpe>, C<scalar>, C<split>, C<study>, and C<undef>.
217
218As some of these have prototypes, C<prototype('CORE::...')> has been
219changed to not make a distinction between overridable and non-overridable
220keywords. This is to make C<prototype('CORE::pos')> consistent with
221C<prototype(&CORE::pos)>.
222
223=head2 C<kill> with negative signal names
224
225C<kill> has always allowed a negative signal number, which kills the
226process group instead of a single process. It has also allowed signal
227names. But it did not behave consistently, because negative signal names
228were treated as 0. Now negative signals names like C<-INT> are supported
229and treated the same way as -2 [perl #112990].
230
231=head1 Security
232
233=head2 C<Storable> security warning in documentation
234
235The documentation for C<Storable> now includes a section which warns readers
236of the danger of accepting Storable documents from untrusted sources. The
237short version is that deserializing certain types of data can lead to loading
238modules and other code execution. This is documented behavior and wanted
239behavior, but this opens an attack vector for malicious entities.
240
241=head2 C<Locale::Maketext> allowed code injection via a malicious template
242
243If users could provide a translation string to Locale::Maketext, this could be
244used to invoke arbitrary Perl subroutines available in the current process.
245
246This has been fixed, but it is still possible to invoke any method provided by
247C<Locale::Maketext> itself or a subclass that you are using. One of these
248methods in turn will invoke the Perl core's C<sprintf> subroutine.
249
250In summary, allowing users to provide translation strings without auditing
251them is a bad idea.
252
253This vulnerability is documented in CVE-2012-6329.
254
255=head2 Avoid calling memset with a negative count
256
257Poorly written perl code that allows an attacker to specify the count to perl's
258C<x> string repeat operator can already cause a memory exhaustion
e612b5a0 259denial-of-service attack. A flaw in versions of perl before v5.15.5 can escalate
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260that into a heap buffer overrun; coupled with versions of glibc before 2.16, it
261possibly allows the execution of arbitrary code.
262
263The flaw addressed to this commit has been assigned identifier CVE-2012-5195
264and was researched by Tim Brown.
265
266=head1 Incompatible Changes
267
268=head2 See also: hash overhaul
269
270Some of the changes in the L<hash overhaul|/"Hash overhaul"> are not fully
271compatible with previous versions of perl. Please read that section.
272
273=head2 An unknown character name in C<\N{...}> is now a syntax error
274
275Previously, it warned, and the Unicode REPLACEMENT CHARACTER was
276substituted. Unicode now recommends that this situation be a syntax
277error. Also, the previous behavior led to some confusing warnings and
278behaviors, and since the REPLACEMENT CHARACTER has no use other than as
279a stand-in for some unknown character, any code that has this problem is
280buggy.
281
282=head2 Formerly deprecated characters in C<\N{}> character name aliases are now errors.
283
284Since v5.12.0, it has been deprecated to use certain characters in
285user-defined C<\N{...}> character names. These now cause a syntax
286error. For example, it is now an error to begin a name with a digit,
287such as in
288
289 my $undraftable = "\N{4F}"; # Syntax error!
290
291or to have commas anywhere in the name. See L<charnames/CUSTOM ALIASES>
292
293=head2 C<\N{BELL}> now refers to U+1F514 instead of U+0007
294
295Unicode 6.0 reused the name "BELL" for a different code point than it
296traditionally had meant. Since Perl v5.14, use of this name still
297referred to U+0007, but would raise a deprecation warning. Now, "BELL"
298refers to U+1F514, and the name for U+0007 is "ALERT". All the
299functions in L<charnames> have been correspondingly updated.
300
301=head2 New Restrictions in Multi-Character Case-Insensitive Matching in Regular Expression Bracketed Character Classes
302
303Unicode has now withdrawn their previous recommendation for regular
304expressions to automatically handle cases where a single character can
305match multiple characters case-insensitively, for example the letter
306LATIN SMALL LETTER SHARP S and the sequence C<ss>. This is because
307it turns out to be impracticable to do this correctly in all
308circumstances. Because Perl has tried to do this as best it can, it
309will continue to do so. (We are considering an option to turn it off.)
310However, a new restriction is being added on such matches when they
311occur in [bracketed] character classes. People were specifying
312things such as C</[\0-\xff]/i>, and being surprised that it matches the
313two character sequence C<ss> (since LATIN SMALL LETTER SHARP S occurs in
314this range). This behavior is also inconsistent with using a
315property instead of a range: C<\p{Block=Latin1}> also includes LATIN
316SMALL LETTER SHARP S, but C</[\p{Block=Latin1}]/i> does not match C<ss>.
317The new rule is that for there to be a multi-character case-insensitive
318match within a bracketed character class, the character must be
319explicitly listed, and not as an end point of a range. This more
320closely obeys the Principle of Least Astonishment. See
321L<perlrecharclass/Bracketed Character Classes>. Note that a bug [perl
322#89774], now fixed as part of this change, prevented the previous
323behavior from working fully.
324
325=head2 Explicit rules for variable names and identifiers
326
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327Due to an oversight, single character variable names in v5.16 were
328completely unrestricted. This opened the door to several kinds of
329insanity. As of v5.18, these now follow the rules of other identifiers,
330in addition to accepting characters that match the C<\p{POSIX_Punct}>
331property.
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332
333There are no longer any differences in the parsing of identifiers
334specified as C<$...> or C<${...}>; previously, they were dealt with in
335different parts of the core, and so had slightly different behavior. For
336instance, C<${foo:bar}> was a legal variable name. Since they are now
337both parsed by the same code, that is no longer the case.
338
339=head2 C<\s> in regular expressions now matches a Vertical Tab
340
341No one could recall why C<\s> didn't match C<\cK>, the vertical tab.
342Now it does. Given the extreme rarity of that character, very little
343breakage is expected.
344
345=head2 C</(?{})/> and C</(??{})/> have been heavily reworked
346
347The implementation of this feature has been almost completely rewritten.
348Although its main intent is to fix bugs, some behaviors, especially
349related to the scope of lexical variables, will have changed. This is
350described more fully in the L</Selected Bug Fixes> section.
351
352=head2 Stricter parsing of substitution replacement
353
354It is no longer possible to abuse the way the parser parses C<s///e> like
355this:
356
357 %_=(_,"Just another ");
358 $_="Perl hacker,\n";
359 s//_}->{_/e;print
360
361=head2 C<given> now aliases the global C<$_>
362
363Instead of assigning to an implicit lexical C<$_>, C<given> now makes the
364global C<$_> an alias for its argument, just like C<foreach>. However, it
365still uses lexical C<$_> if there is lexical C<$_> in scope (again, just like
366C<foreach>) [perl #114020].
367
368=head2 Lexical C<$_> is now experimental
369
e612b5a0 370Since it was introduced in Perl v5.10, it has caused much confusion with no
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371obvious solution:
372
373=over
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374
375=item *
376
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377Various modules (e.g., List::Util) expect callback routines to use the
378global C<$_>. C<use List::Util 'first'; my $_; first { $_ == 1 } @list>
379does not work as one would expect.
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380
381=item *
382
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383A C<my $_> declaration earlier in the same file can cause confusing closure
384warnings.
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385
386=item *
387
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388The "_" subroutine prototype character allows called subroutines to access
389your lexical C<$_>, so it is not really private after all.
2426c394 390
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391=item *
392
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393Nevertheless, subroutines with a "(@)" prototype and methods cannot access
394the caller's lexical C<$_>, unless they are written in XS.
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395
396=item *
397
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398But even XS routines cannot access a lexical C<$_> declared, not in the
399calling subroutine, but in an outer scope, iff that subroutine happened not
400to mention C<$_> or use any operators that default to C<$_>.
401
402=back
403
404It is our hope that lexical C<$_> can be rehabilitated, but this may
405cause changes in its behavior. Please use it with caution until it
406becomes stable.
407
408=head2 readline() with C<$/ = \N> now reads N characters, not N bytes
409
410Previously, when reading from a stream with I/O layers such as
411C<encoding>, the readline() function, otherwise known as the C<< <> >>
412operator, would read I<N> bytes from the top-most layer. [perl #79960]
413
414Now, I<N> characters are read instead.
415
416There is no change in behaviour when reading from streams with no
417extra layers, since bytes map exactly to characters.
418
419=head2 Overridden C<glob> is now passed one argument
420
421C<glob> overrides used to be passed a magical undocumented second argument
422that identified the caller. Nothing on CPAN was using this, and it got in
423the way of a bug fix, so it was removed. If you really need to identify
424the caller, see L<Devel::Callsite> on CPAN.
425
426=head2 Here-doc parsing
427
428The body of a here-document inside a quote-like operator now always begins
429on the line after the "<<foo" marker. Previously, it was documented to
430begin on the line following the containing quote-like operator, but that
431was only sometimes the case [perl #114040].
432
433=head2 Alphanumeric operators must now be separated from the closing
434delimiter of regular expressions
435
436You may no longer write something like:
437
438 m/a/and 1
439
440Instead you must write
441
442 m/a/ and 1
443
444with whitespace separating the operator from the closing delimiter of
445the regular expression. Not having whitespace has resulted in a
446deprecation warning since Perl v5.14.0.
447
448=head2 qw(...) can no longer be used as parentheses
449
450C<qw> lists used to fool the parser into thinking they were always
451surrounded by parentheses. This permitted some surprising constructions
452such as C<foreach $x qw(a b c) {...}>, which should really be written
453C<foreach $x (qw(a b c)) {...}>. These would sometimes get the lexer into
454the wrong state, so they didn't fully work, and the similar C<foreach qw(a
455b c) {...}> that one might expect to be permitted never worked at all.
456
457This side effect of C<qw> has now been abolished. It has been deprecated
e612b5a0 458since Perl v5.13.11. It is now necessary to use real parentheses
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459everywhere that the grammar calls for them.
460
461=head2 Interaction of lexical and default warnings
462
463Turning on any lexical warnings used first to disable all default warnings
464if lexical warnings were not already enabled:
465
466 $*; # deprecation warning
467 use warnings "void";
468 $#; # void warning; no deprecation warning
469
f105b7be 470Now, the C<debugging>, C<deprecated>, C<glob>, C<inplace> and C<malloc> warnings
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471categories are left on when turning on lexical warnings (unless they are
472turned off by C<no warnings>, of course).
473
474This may cause deprecation warnings to occur in code that used to be free
475of warnings.
476
477Those are the only categories consisting only of default warnings. Default
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478warnings in other categories are still disabled by C<< use warnings "category" >>,
479as we do not yet have the infrastructure for controlling
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480individual warnings.
481
482=head2 C<state sub> and C<our sub>
483
484Due to an accident of history, C<state sub> and C<our sub> were equivalent
485to a plain C<sub>, so one could even create an anonymous sub with
486C<our sub { ... }>. These are now disallowed outside of the "lexical_subs"
487feature. Under the "lexical_subs" feature they have new meanings described
488in L<perlsub/Lexical Subroutines>.
489
490=head2 Defined values stored in environment are forced to byte strings
491
492A value stored in an environment variable has always been stringified. In this
493release, it is converted to be only a byte string. First, it is forced to be a
494only a string. Then if the string is utf8 and the equivalent of
495C<utf8::downgrade()> works, that result is used; otherwise, the equivalent of
496C<utf8::encode()> is used, and a warning is issued about wide characters
497(L</Diagnostics>).
498
499=head2 C<require> dies for unreadable files
500
501When C<require> encounters an unreadable file, it now dies. It used to
502ignore the file and continue searching the directories in C<@INC>
503[perl #113422].
504
505=head2 C<gv_fetchmeth_*> and SUPER
506
507The various C<gv_fetchmeth_*> XS functions used to treat a package whose
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508named ended with C<::SUPER> specially. A method lookup on the C<Foo::SUPER>
509package would be treated as a C<SUPER> method lookup on the C<Foo> package. This
510is no longer the case. To do a C<SUPER> lookup, pass the C<Foo> stash and the
511C<GV_SUPER> flag.
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512
513=head2 C<split>'s first argument is more consistently interpreted
514
e612b5a0 515After some changes earlier in v5.17, C<split>'s behavior has been
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516simplified: if the PATTERN argument evaluates to a literal string
517containing one space, it is treated the way that a I<literal> string
518containing one space once was.
519
520=head1 Deprecations
521
522=head2 Deprecated modules
523
524The following modules will be removed from the core distribution in a
525future release, and should be installed from CPAN instead. Distributions
526on CPAN which require these should add them to their prerequisites.
f105b7be 527The core versions of these modules will issue C<"deprecated">-category
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528warnings.
529
530You can silence these deprecation warnings by installing the modules
531in question from CPAN.
532
533=over
534
535=item L<Archive::Extract>
536
537=item L<B::Lint>
538
539=item L<B::Lint::Debug>
540
541=item L<CPANPLUS> and all included C<CPANPLUS::*> modules
542
543=item L<Devel::InnerPackage>
544
545=item L<encoding>
546
547=item L<Log::Message>
548
549=item L<Log::Message::Config>
550
551=item L<Log::Message::Handlers>
552
553=item L<Log::Message::Item>
554
555=item L<Log::Message::Simple>
556
557=item L<Module::Pluggable>
558
559=item L<Module::Pluggable::Object>
560
561=item L<Object::Accessor>
562
563=item L<Pod::LaTeX>
564
565=item L<Term::UI>
566
567=item L<Term::UI::History>
568
569=back
570
571=head2 Deprecated Utilities
572
573The following utilities will be removed from the core distribution in a
574future release as their associated modules have been deprecated. They
575will remain available with the applicable CPAN distribution.
576
577=over
578
579=item L<cpanp>
580
581=item C<cpanp-run-perl>
582
583=item L<cpan2dist>
584
585These items are part of the C<CPANPLUS> distribution.
586
587=item L<pod2latex>
588
589This item is part of the C<Pod::LaTeX> distribution.
590
591=back
592
593=head2 PL_sv_objcount
594
595This interpreter-global variable used to track the total number of
596Perl objects in the interpreter. It is no longer maintained and will
e612b5a0 597be removed altogether in Perl v5.20.
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598
599=head2 Five additional characters should be escaped in patterns with C</x>
600
601When a regular expression pattern is compiled with C</x>, Perl treats 6
602characters as white space to ignore, such as SPACE and TAB. However,
603Unicode recommends 11 characters be treated thusly. We will conform
604with this in a future Perl version. In the meantime, use of any of the
605missing characters will raise a deprecation warning, unless turned off.
606The five characters are:
f105b7be
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607
608 U+0085 NEXT LINE,
609 U+200E LEFT-TO-RIGHT MARK,
610 U+200F RIGHT-TO-LEFT MARK,
611 U+2028 LINE SEPARATOR,
612
5ed58cbd 613and
f105b7be
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614
615 U+2029 PARAGRAPH SEPARATOR.
5ed58cbd
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616
617=head2 User-defined charnames with surprising whitespace
618
619A user-defined character name with trailing or multiple spaces in a row is
620likely a typo. This now generates a warning when defined, on the assumption
621that uses of it will be unlikely to include the excess whitespace.
622
623=head2 Various XS-callable functions are now deprecated
624
625All the functions used to classify characters will be removed from a
626future version of Perl, and should not be used. With participating C
627compilers (e.g., gcc), compiling any file that uses any of these will
628generate a warning. These were not intended for public use; there are
629equivalent, faster, macros for most of them.
e612b5a0 630
2e7bc647 631See L<perlapi/Character classes>. The complete list is:
e612b5a0 632
5ed58cbd
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633C<is_uni_alnum>, C<is_uni_alnumc>, C<is_uni_alnumc_lc>,
634C<is_uni_alnum_lc>, C<is_uni_alpha>, C<is_uni_alpha_lc>,
635C<is_uni_ascii>, C<is_uni_ascii_lc>, C<is_uni_blank>,
636C<is_uni_blank_lc>, C<is_uni_cntrl>, C<is_uni_cntrl_lc>,
637C<is_uni_digit>, C<is_uni_digit_lc>, C<is_uni_graph>,
638C<is_uni_graph_lc>, C<is_uni_idfirst>, C<is_uni_idfirst_lc>,
639C<is_uni_lower>, C<is_uni_lower_lc>, C<is_uni_print>,
640C<is_uni_print_lc>, C<is_uni_punct>, C<is_uni_punct_lc>,
641C<is_uni_space>, C<is_uni_space_lc>, C<is_uni_upper>,
642C<is_uni_upper_lc>, C<is_uni_xdigit>, C<is_uni_xdigit_lc>,
643C<is_utf8_alnum>, C<is_utf8_alnumc>, C<is_utf8_alpha>,
644C<is_utf8_ascii>, C<is_utf8_blank>, C<is_utf8_char>,
645C<is_utf8_cntrl>, C<is_utf8_digit>, C<is_utf8_graph>,
646C<is_utf8_idcont>, C<is_utf8_idfirst>, C<is_utf8_lower>,
647C<is_utf8_mark>, C<is_utf8_perl_space>, C<is_utf8_perl_word>,
648C<is_utf8_posix_digit>, C<is_utf8_print>, C<is_utf8_punct>,
649C<is_utf8_space>, C<is_utf8_upper>, C<is_utf8_xdigit>,
650C<is_utf8_xidcont>, C<is_utf8_xidfirst>.
651
652In addition these three functions that have never worked properly are
653deprecated:
654C<to_uni_lower_lc>, C<to_uni_title_lc>, and C<to_uni_upper_lc>.
655
f105b7be 656=head2 Certain rare uses of backslashes within regexes are now deprecated
5ed58cbd
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657
658There are three pairs of characters that Perl recognizes as
659metacharacters in regular expression patterns: C<{}>, C<[]>, and C<()>.
660These can be used as well to delimit patterns, as in:
661
662 m{foo}
663 s(foo)(bar)
664
665Since they are metacharacters, they have special meaning to regular
666expression patterns, and it turns out that you can't turn off that
667special meaning by the normal means of preceding them with a backslash,
f105b7be 668if you use them, paired, within a pattern delimited by them. For
5ed58cbd
RS
669example, in
670
671 m{foo\{1,3\}}
672
673the backslashes do not change the behavior, and this matches
674S<C<"f o">> followed by one to three more occurrences of C<"o">.
675
676Usages like this, where they are interpreted as metacharacters, are
677exceedingly rare; we think there are none, for example, in all of CPAN.
678Hence, this deprecation should affect very little code. It does give
679notice, however, that any such code needs to change, which will in turn
680allow us to change the behavior in future Perl versions so that the
681backslashes do have an effect, and without fear that we are silently
682breaking any existing code.
683
d5f315e8
KW
684=head2 Splitting the tokens C<(?> and C<(*> in regular expressions
685
686A deprecation warning is now raised if the C<(> and C<?> are separated
687by white space or comments in C<(?...)> regular expression constructs.
688Similarly, if the C<(> and C<*> are separated in C<(*VERB...)>
689constructs.
690
e0a1dec5
LT
691=head2 Pre-PerlIO IO implementations
692
693Perl supports being built without PerlIO proper, using a stdio or sfio
694wrapper instead. A perl build like this will not support IO layers and
695thus Unicode IO, making it rather handicapped.
696
697PerlIO supports a C<stdio> layer if stdio use is desired, and similarly a
698sfio layer could be produced.
699
5ed58cbd
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700=head1 Future Deprecations
701
702=over
71e6aba6
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703
704=item *
705
4263dd11 706Platforms without support infrastructure
5ed58cbd
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707
708Both Windows CE and z/OS have been historically under-maintained, and are
709currently neither successfully building nor regularly being smoke tested.
710Efforts are underway to change this situation, but it should not be taken for
711granted that the platforms are safe and supported. If they do not become
712buildable and regularly smoked, support for them may be actively removed in
713future releases. If you have an interest in these platforms and you can lend
714your time, expertise, or hardware to help support these platforms, please let
715the perl development effort know by emailing C<perl5-porters@perl.org>.
716
717Some platforms that appear otherwise entirely dead are also on the short list
e612b5a0 718for removal between now and v5.20.0:
5ed58cbd
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719
720=over
721
722=item DG/UX
723
724=item NeXT
725
726=back
1993add8 727
ec985017
RS
728We also think it likely that current versions of Perl will no longer
729build AmigaOS, DJGPP, NetWare (natively), OS/2 and Plan 9. If you
730are using Perl on such a platform and have an interest in ensuring
731Perl's future on them, please contact us.
732
733We believe that Perl has long been unable to build on mixed endian
734architectures (such as PDP-11s), and intend to remove any remain
735support code. Similarly, code supporting the long umaintained GNU
736dld will be removed soon if no-one makes themselves known as an
737active user.
738
1993add8
RS
739=item *
740
5ed58cbd
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741Swapping of $< and $>
742
743For more information about this future deprecation, see L<the relevant RT
744ticket|https://rt.perl.org/rt3/Ticket/Display.html?id=96212>.
71e6aba6
RS
745
746=item *
747
5ed58cbd 748C<microperl>, long broken and of unclear present purpose, will be removed.
71e6aba6
RS
749
750=item *
751
5ed58cbd
RS
752Revamping C<< "\Q" >> semantics in double-quotish strings when combined with
753other escapes.
754
755There are several bugs and inconsistencies involving combinations
756of C<\Q> and escapes like C<\x>, C<\L>, etc., within a C<\Q...\E> pair.
757These need to be fixed, and doing so will necessarily change current
758behavior. The changes have not yet been settled.
71e6aba6 759
d5f315e8
KW
760=item *
761
762Use of C<$^>, where C<^> stands for any actual (non-printing) C0 control
763character will be disallowed in a future Perl version. Use C<${^}>
764instead (where again C<^> stands for a control character),
765or better, C<$^A> , where C<^> this time is a caret (CIRCUMFLEX ACCENT),
766and C<A> stands for any of the characters listed at the end of
767L<perlebcdic/OPERATOR DIFFERENCES>.
768
337fb649 769=back
2426c394 770
5ed58cbd
RS
771=head1 Performance Enhancements
772
773=over 4
2426c394 774
5ed58cbd 775=item *
2426c394 776
5ed58cbd
RS
777Lists of lexical variable declarations (C<my($x, $y)>) are now optimised
778down to a single op and are hence faster than before.
2426c394 779
5ed58cbd 780=item *
2426c394 781
5ed58cbd
RS
782A new C preprocessor define C<NO_TAINT_SUPPORT> was added that, if set,
783disables Perl's taint support altogether. Using the -T or -t command
784line flags will cause a fatal error. Beware that both core tests as
785well as many a CPAN distribution's tests will fail with this change. On
786the upside, it provides a small performance benefit due to reduced
787branching.
2426c394 788
5ed58cbd
RS
789B<Do not enable this unless you know exactly what you are getting yourself
790into.>
791
792=item *
793
794C<pack> with constant arguments is now constant folded in most cases
795[perl #113470].
796
797=item *
798
799Speed up in regular expression matching against Unicode properties. The
800largest gain is for C<\X>, the Unicode "extended grapheme cluster." The
801gain for it is about 35% - 40%. Bracketed character classes, e.g.,
802C<[0-9\x{100}]> containing code points above 255 are also now faster.
803
804=item *
805
806On platforms supporting it, several former macros are now implemented as static
807inline functions. This should speed things up slightly on non-GCC platforms.
808
809=item *
810
66f62cf6
RS
811The optimisation of hashes in boolean context has been extended to
812affect C<scalar(%hash)>, C<%hash ? ... : ...>, and C<sub { %hash || ... }>.
5ed58cbd
RS
813
814=item *
815
f105b7be 816Filetest operators manage the stack in a fractionally more efficient manner.
5ed58cbd
RS
817
818=item *
819
820Globs used in a numeric context are now numified directly in most cases,
f105b7be 821rather than being numified via stringification.
5ed58cbd
RS
822
823=item *
824
825The C<x> repetition operator is now folded to a single constant at compile
826time if called in scalar context with constant operands and no parentheses
827around the left operand.
828
829=back
830
831=head1 Modules and Pragmata
832
833=head2 New Modules and Pragmata
2426c394 834
337fb649 835=over 4
982110e0 836
82d98f72 837=item *
2426c394 838
5ed58cbd
RS
839L<Config::Perl::V> version 0.16 has been added as a dual-lifed module.
840It provides structured data retrieval of C<perl -V> output including
841information only known to the C<perl> binary and not available via L<Config>.
842
843=back
844
845=head2 Updated Modules and Pragmata
846
9863976f 847For a complete list of updates, run:
5ed58cbd 848
f105b7be 849 $ corelist --diff 5.16.0 5.18.0
5ed58cbd 850
e612b5a0 851You can substitute your favorite version in place of C<5.16.0>, too.
5ed58cbd 852
5ed58cbd
RS
853=head2 Removed Modules and Pragmata
854
855=over
33392251
BF
856
857=item *
858
5ed58cbd
RS
859L<Version::Requirements> has been removed from the core distribution. It is
860available under a different name: L<CPAN::Meta::Requirements>.
2426c394 861
337fb649 862=back
2426c394 863
5ed58cbd 864=head1 Documentation
19718730 865
5ed58cbd
RS
866=head2 Changes to Existing Documentation
867
868=head3 L<perlcheat>
82d98f72 869
5a6a30f4 870=over 4
b7c7d786 871
5ed58cbd
RS
872=item *
873
874L<perlcheat> has been reorganized, and a few new sections were added.
875
876=back
877
878=head3 L<perldata>
879
880=over 4
82d98f72 881
5ed58cbd 882=item *
d2d1e842 883
5ed58cbd
RS
884Now explicitly documents the behaviour of hash initializer lists that
885contain duplicate keys.
f355e93d 886
5a6a30f4 887=back
f355e93d 888
5ed58cbd 889=head3 L<perldiag>
19718730 890
19718730 891=over 4
e14ac59b 892
5ed58cbd
RS
893=item *
894
895The explanation of symbolic references being prevented by "strict refs"
896now doesn't assume that the reader knows what symbolic references are.
897
898=back
9f351b45 899
5ed58cbd 900=head3 L<perlfaq>
9f351b45 901
5ed58cbd 902=over 4
9f351b45 903
5ed58cbd 904=item *
7cf3104f 905
5ed58cbd 906L<perlfaq> has been synchronized with version 5.0150040 from CPAN.
12719193 907
6253ee75 908=back
216cf7fc 909
5ed58cbd 910=head3 L<perlfunc>
f5b73711 911
5ed58cbd
RS
912=over 4
913
914=item *
a75569c0 915
5ed58cbd 916The return value of C<pipe> is now documented.
a75569c0 917
5ed58cbd 918=item *
a75569c0 919
5ed58cbd
RS
920Clarified documentation of C<our>.
921
922=back
923
924=head3 L<perlop>
925
926=over 4
927
928=item *
929
930Loop control verbs (C<dump>, C<goto>, C<next>, C<last> and C<redo>) have always
931had the same precedence as assignment operators, but this was not documented
932until now.
933
934=back
935
936=head3 Diagnostics
937
938The following additions or changes have been made to diagnostic output,
939including warnings and fatal error messages. For the complete list of
940diagnostic messages, see L<perldiag>.
941
5ed58cbd
RS
942=head2 New Diagnostics
943
5ed58cbd
RS
944=head3 New Errors
945
946=over 4
947
948=item *
949
950L<Unterminated delimiter for here document|perldiag/"Unterminated delimiter for here document">
951
952This message now occurs when a here document label has an initial quotation
953mark but the final quotation mark is missing.
954
955This replaces a bogus and misleading error message about not finding the label
956itself [perl #114104].
957
958=item *
959
960L<panic: child pseudo-process was never scheduled|perldiag/"panic: child pseudo-process was never scheduled">
961
962This error is thrown when a child pseudo-process in the ithreads implementation
963on Windows was not scheduled within the time period allowed and therefore was
964not able to initialize properly [perl #88840].
965
966=item *
967
968L<Group name must start with a non-digit word character in regex; marked by <-- HERE in mE<sol>%sE<sol>|perldiag/"Group name must start with a non-digit word character in regex; marked by <-- HERE in m/%s/">
969
970This error has been added for C<(?&0)>, which is invalid. It used to
971produce an incomprehensible error message [perl #101666].
972
973=item *
974
975L<Can't use an undefined value as a subroutine reference|perldiag/"Can't use an undefined value as %s reference">
976
977Calling an undefined value as a subroutine now produces this error message.
978It used to, but was accidentally disabled, first in Perl 5.004 for
e612b5a0 979non-magical variables, and then in Perl v5.14 for magical (e.g., tied)
5ed58cbd
RS
980variables. It has now been restored. In the mean time, undef was treated
981as an empty string [perl #113576].
982
983=item *
984
985L<Experimental "%s" subs not enabled|perldiag/"Experimental "%s" subs not enabled">
986
987To use lexical subs, you must first enable them:
988
989 no warnings 'experimental::lexical_subs';
990 use feature 'lexical_subs';
991 my sub foo { ... }
992
993=back
994
995=head3 New Warnings
996
997=over 4
998
999=item *
1000
5ed58cbd
RS
1001Strings with code points over 0xFF may not be mapped into in-memory file
1002handles
1003
1004=item *
1005
1006L<'%s' resolved to '\o{%s}%d'|perldiag/"'%s' resolved to '\o{%s}%d'">
1007
1008=item *
1009
1010L<'Trailing white-space in a charnames alias definition is deprecated'|perldiag/"Trailing white-space in a charnames alias definition is deprecated">
1011
1012=item *
1013
1014L<'A sequence of multiple spaces in a charnames alias definition is deprecated'|perldiag/"A sequence of multiple spaces in a charnames alias definition is deprecated">
1015
1016=item *
1017
1018L<'Passing malformed UTF-8 to "%s" is deprecated'|perldiag/"Passing malformed UTF-8 to "%s" is deprecated">
1019
1020=item *
1021
1022L<Subroutine "&%s" is not available|perldiag/"Subroutine "&%s" is not available">
1023
1024(W closure) During compilation, an inner named subroutine or eval is
1025attempting to capture an outer lexical subroutine that is not currently
1026available. This can happen for one of two reasons. First, the lexical
1027subroutine may be declared in an outer anonymous subroutine that has not
1028yet been created. (Remember that named subs are created at compile time,
1029while anonymous subs are created at run-time.) For example,
1030
1031 sub { my sub a {...} sub f { \&a } }
1032
1033At the time that f is created, it can't capture the current the "a" sub,
1034since the anonymous subroutine hasn't been created yet. Conversely, the
1035following won't give a warning since the anonymous subroutine has by now
1036been created and is live:
1037
1038 sub { my sub a {...} eval 'sub f { \&a }' }->();
1039
1040The second situation is caused by an eval accessing a variable that has
1041gone out of scope, for example,
1042
1043 sub f {
1044 my sub a {...}
1045 sub { eval '\&a' }
1046 }
1047 f()->();
1048
1049Here, when the '\&a' in the eval is being compiled, f() is not currently
1050being executed, so its &a is not available for capture.
1051
1052=item *
1053
1054L<"%s" subroutine &%s masks earlier declaration in same %s|perldiag/"%s" subroutine &%s masks earlier declaration in same %s>
1055
1056(W misc) A "my" or "state" subroutine has been redeclared in the
1057current scope or statement, effectively eliminating all access to
1058the previous instance. This is almost always a typographical error.
1059Note that the earlier subroutine will still exist until the end of
1060the scope or until all closure references to it are destroyed.
1061
1062=item *
1063
1064L<The %s feature is experimental|perldiag/"The %s feature is experimental">
1065
1066(S experimental) This warning is emitted if you enable an experimental
1067feature via C<use feature>. Simply suppress the warning if you want
1068to use the feature, but know that in doing so you are taking the risk
1069of using an experimental feature which may change or be removed in a
1070future Perl version:
1071
1072 no warnings "experimental::lexical_subs";
1073 use feature "lexical_subs";
1074
1075=item *
1076
1077L<sleep(%u) too large|perldiag/"sleep(%u) too large">
1078
1079(W overflow) You called C<sleep> with a number that was larger than it can
1080reliably handle and C<sleep> probably slept for less time than requested.
1081
1082=item *
1083
1084L<Wide character in setenv|perldiag/"Wide character in %s">
1085
1086Attempts to put wide characters into environment variables via C<%ENV> now
1087provoke this warning.
1088
1089=item *
1090
1091"L<Invalid negative number (%s) in chr|perldiag/"Invalid negative number (%s) in chr">"
1092
1093C<chr()> now warns when passed a negative value [perl #83048].
1094
1095=item *
1096
1097"L<Integer overflow in srand|perldiag/"Integer overflow in srand">"
1098
1099C<srand()> now warns when passed a value that doesn't fit in a C<UV> (since the
1100value will be truncated rather than overflowing) [perl #40605].
1101
1102=item *
1103
1104"L<-i used with no filenames on the command line, reading from STDIN|perldiag/"-i used with no filenames on the command line, reading from STDIN">"
1105
1106Running perl with the C<-i> flag now warns if no input files are provided on
1107the command line [perl #113410].
1108
1109=back
1110
1111=head2 Changes to Existing Diagnostics
1112
1113=over 4
1114
1115=item *
1116
1117L<$* is no longer supported|perldiag/"$* is no longer supported">
1118
1119The warning that use of C<$*> and C<$#> is no longer supported is now
1120generated for every location that references them. Previously it would fail
1121to be generated if another variable using the same typeglob was seen first
1122(e.g. C<@*> before C<$*>), and would not be generated for the second and
1123subsequent uses. (It's hard to fix the failure to generate warnings at all
1124without also generating them every time, and warning every time is
1125consistent with the warnings that C<$[> used to generate.)
1126
1127=item *
1128
1129The warnings for C<\b{> and C<\B{> were added. They are a deprecation
1130warning which should be turned off by that category. One should not
1131have to turn off regular regexp warnings as well to get rid of these.
1132
1133=item *
1134
1135L<Constant(%s): Call to &{$^H{%s}} did not return a defined value|perldiag/Constant(%s): Call to &{$^H{%s}} did not return a defined value>
1136
1137Constant overloading that returns C<undef> results in this error message.
1138For numeric constants, it used to say "Constant(undef)". "undef" has been
1139replaced with the number itself.
1140
1141=item *
1142
1143The error produced when a module cannot be loaded now includes a hint that
1144the module may need to be installed: "Can't locate hopping.pm in @INC (you
1145may need to install the hopping module) (@INC contains: ...)"
1146
1147=item *
1148
1149L<vector argument not supported with alpha versions|perldiag/vector argument not supported with alpha versions>
1150
1151This warning was not suppressable, even with C<no warnings>. Now it is
1152suppressible, and has been moved from the "internal" category to the
1153"printf" category.
1154
1155=item *
1156
1157C<< Can't do {n,m} with n > m in regex; marked by <-- HERE in m/%s/ >>
1158
1159This fatal error has been turned into a warning that reads:
1160
1161L<< Quantifier {n,m} with n > m can't match in regex | perldiag/Quantifier {n,m} with n > m can't match in regex >>
1162
1163(W regexp) Minima should be less than or equal to maxima. If you really want
1164your regexp to match something 0 times, just put {0}.
1165
1166=item *
1167
1168The "Runaway prototype" warning that occurs in bizarre cases has been
1169removed as being unhelpful and inconsistent.
1170
1171=item *
1172
1173The "Not a format reference" error has been removed, as the only case in
1174which it could be triggered was a bug.
1175
1176=item *
1177
1178The "Unable to create sub named %s" error has been removed for the same
1179reason.
1180
1181=item *
1182
1183The 'Can't use "my %s" in sort comparison' error has been downgraded to a
1184warning, '"my %s" used in sort comparison' (with 'state' instead of 'my'
1185for state variables). In addition, the heuristics for guessing whether
1186lexical $a or $b has been misused have been improved to generate fewer
1187false positives. Lexical $a and $b are no longer disallowed if they are
1188outside the sort block. Also, a named unary or list operator inside the
1189sort block no longer causes the $a or $b to be ignored [perl #86136].
1190
1191=back
1192
1193=head1 Utility Changes
1194
1195=head3 L<h2xs>
1196
1197=over 4
1198
1199=item *
1200
1201F<h2xs> no longer produces invalid code for empty defines. [perl #20636]
1202
1203=back
1204
1205=head1 Configuration and Compilation
1206
1207=over 4
1208
1209=item *
1210
1211Added C<useversionedarchname> option to Configure
1212
1213When set, it includes 'api_versionstring' in 'archname'. E.g.
1214x86_64-linux-5.13.6-thread-multi. It is unset by default.
1215
1216This feature was requested by Tim Bunce, who observed that
f105b7be 1217C<INSTALL_BASE> creates a library structure that does not
5ed58cbd
RS
1218differentiate by perl version. Instead, it places architecture
1219specific files in "$install_base/lib/perl5/$archname". This makes
f105b7be 1220it difficult to use a common C<INSTALL_BASE> library path with
5ed58cbd
RS
1221multiple versions of perl.
1222
f105b7be 1223By setting C<-Duseversionedarchname>, the $archname will be
c2959982 1224distinct for architecture I<and> API version, allowing mixed use of
f105b7be 1225C<INSTALL_BASE>.
5ed58cbd
RS
1226
1227=item *
1228
ff772877
RS
1229Add a C<PERL_NO_INLINE_FUNCTIONS> option
1230
f105b7be 1231If C<PERL_NO_INLINE_FUNCTIONS> is defined, don't include "inline.h"
ff772877
RS
1232
1233This permits test code to include the perl headers for definitions without
1234creating a link dependency on the perl library (which may not exist yet).
1235
1236=item *
1237
5ed58cbd
RS
1238Configure will honour the external C<MAILDOMAIN> environment variable, if set.
1239
1240=item *
1241
1242C<installman> no longer ignores the silent option
1243
1244=item *
1245
1246Both C<META.yml> and C<META.json> files are now included in the distribution.
1247
1248=item *
1249
1250F<Configure> will now correctly detect C<isblank()> when compiling with a C++
1251compiler.
1252
1253=item *
1254
1255The pager detection in F<Configure> has been improved to allow responses which
1256specify options after the program name, e.g. B</usr/bin/less -R>, if the user
1257accepts the default value. This helps B<perldoc> when handling ANSI escapes
1258[perl #72156].
1259
1260=back
1261
1262=head1 Testing
1263
1264=over 4
1265
1266=item *
1267
1268The test suite now has a section for tests that require very large amounts
1269of memory. These tests won't run by default; they can be enabled by
1270setting the C<PERL_TEST_MEMORY> environment variable to the number of
1271gibibytes of memory that may be safely used.
1272
1273=back
1274
1275=head1 Platform Support
1276
1277=head2 Discontinued Platforms
1278
1279=over 4
1280
1281=item BeOS
1282
1283BeOS was an operating system for personal computers developed by Be Inc,
1284initially for their BeBox hardware. The OS Haiku was written as an open
1285source replacement for/continuation of BeOS, and its perl port is current and
1286actively maintained.
1287
1288=item UTS Global
1289
1290Support code relating to UTS global has been removed. UTS was a mainframe
1291version of System V created by Amdahl, subsequently sold to UTS Global. The
e612b5a0 1292port has not been touched since before Perl v5.8.0, and UTS Global is now
5ed58cbd
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1293defunct.
1294
1295=item VM/ESA
1296
1297Support for VM/ESA has been removed. The port was tested on 2.3.0, which
1298IBM ended service on in March 2002. 2.4.0 ended service in June 2003, and
1299was superseded by Z/VM. The current version of Z/VM is V6.2.0, and scheduled
1300for end of service on 2015/04/30.
1301
1302=item MPE/IX
1303
1304Support for MPE/IX has been removed.
1305
1306=item EPOC
1307
1308Support code relating to EPOC has been removed. EPOC was a family of
1309operating systems developed by Psion for mobile devices. It was the
1310predecessor of Symbian. The port was last updated in April 2002.
1311
1312=item Rhapsody
1313
1314Support for Rhapsody has been removed.
1315
1316=back
1317
1318=head2 Platform-Specific Notes
1319
1320=head3 AIX
1321
1322Configure now always adds C<-qlanglvl=extc99> to the CC flags on AIX when
1323using xlC. This will make it easier to compile a number of XS-based modules
1324that assume C99 [perl #113778].
1325
1326=head3 clang++
1327
1328There is now a workaround for a compiler bug that prevented compiling
e612b5a0 1329with clang++ since Perl v5.15.7 [perl #112786].
5ed58cbd
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1330
1331=head3 C++
1332
1333When compiling the Perl core as C++ (which is only semi-supported), the
1334mathom functions are now compiled as C<extern "C">, to ensure proper
1335binary compatibility. (However, binary compatibility isn't generally
1336guaranteed anyway in the situations where this would matter.)
1337
1338=head3 Darwin
1339
1340Stop hardcoding an alignment on 8 byte boundaries to fix builds using
1341-Dusemorebits.
1342
1343=head3 Haiku
1344
1345Perl should now work out of the box on Haiku R1 Alpha 4.
1346
1347=head3 MidnightBSD
1348
1349C<libc_r> was removed from recent versions of MidnightBSD and older versions
1350work better with C<pthread>. Threading is now enabled using C<pthread> which
1351corrects build errors with threading enabled on 0.4-CURRENT.
1352
1353=head3 Solaris
1354
1355In Configure, avoid running sed commands with flags not supported on Solaris.
1356
1357=head3 VMS
1358
1359=over
1360
1361=item *
1362
1363Where possible, the case of filenames and command-line arguments is now
1364preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
1365C<DECC$ARGV_PARSE_STYLE> at start-up time. The latter only takes effect
1366when extended parse is enabled in the process from which Perl is run.
1367
1368=item *
1369
1370The character set for Extended Filename Syntax (EFS) is now enabled by default
1371on VMS. Among other things, this provides better handling of dots in directory
05f5908f 1372names, multiple dots in filenames, and spaces in filenames. To obtain the old
5ed58cbd
RS
1373behavior, set the logical name C<DECC$EFS_CHARSET> to C<DISABLE>.
1374
1375=item *
1376
05f5908f 1377Fixed linking on builds configured with C<-Dusemymalloc=y>.
5ed58cbd
RS
1378
1379=item *
1380
05f5908f
CB
1381Experimental support for building Perl with the HP C++ compiler is available
1382by configuring with C<-Dusecxx>.
5ed58cbd
RS
1383
1384=item *
1385
1386All C header files from the top-level directory of the distribution are now
1387installed on VMS, providing consistency with a long-standing practice on other
1388platforms. Previously only a subset were installed, which broke non-core
1389extension builds for extensions that depended on the missing include files.
1390
1391=item *
1392
1393Quotes are now removed from the command verb (but not the parameters) for
1394commands spawned via C<system>, backticks, or a piped C<open>. Previously,
1395quotes on the verb were passed through to DCL, which would fail to recognize
1396the command. Also, if the verb is actually a path to an image or command
1397procedure on an ODS-5 volume, quoting it now allows the path to contain spaces.
1398
1399=item *
1400
1401The B<a2p> build has been fixed for the HP C++ compiler on OpenVMS.
1402
1403=back
1404
1405=head3 Win32
1406
1407=over
1408
1409=item *
1410
1411Perl can now be built using Microsoft's Visual C++ 2012 compiler by specifying
1412CCTYPE=MSVC110 (or MSVC110FREE if you are using the free Express edition for
1413Windows Desktop) in F<win32/Makefile>.
1414
1415=item *
1416
f105b7be 1417The option to build without C<USE_SOCKETS_AS_HANDLES> has been removed.
5ed58cbd
RS
1418
1419=item *
1420
1421Fixed a problem where perl could crash while cleaning up threads (including the
1422main thread) in threaded debugging builds on Win32 and possibly other platforms
1423[perl #114496].
1424
1425=item *
1426
1427A rare race condition that would lead to L<sleep|perlfunc/sleep> taking more
1428time than requested, and possibly even hanging, has been fixed [perl #33096].
1429
1430=item *
1431
1432C<link> on Win32 now attempts to set C<$!> to more appropriate values
1433based on the Win32 API error code. [perl #112272]
1434
1435Perl no longer mangles the environment block, e.g. when launching a new
1436sub-process, when the environment contains non-ASCII characters. Known
1437problems still remain, however, when the environment contains characters
1438outside of the current ANSI codepage (e.g. see the item about Unicode in
1439C<%ENV> in L<http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod>).
1440[perl #113536]
1441
1442=item *
1443
1444Building perl with some Windows compilers used to fail due to a problem
1445with miniperl's C<glob> operator (which uses the C<perlglob> program)
1446deleting the PATH environment variable [perl #113798].
1447
1448=item *
1449
f105b7be 1450A new makefile option, C<USE_64_BIT_INT>, has been added to the Windows
5ed58cbd
RS
1451makefiles. Set this to "define" when building a 32-bit perl if you want
1452it to use 64-bit integers.
1453
1454Machine code size reductions, already made to the DLLs of XS modules in
e612b5a0 1455Perl v5.17.2, have now been extended to the perl DLL itself.
5ed58cbd 1456
e612b5a0 1457Building with VC++ 6.0 was inadvertently broken in Perl v5.17.2 but has
5ed58cbd
RS
1458now been fixed again.
1459
1460=back
1461
1462=head3 WinCE
1463
1464Building on WinCE is now possible once again, although more work is required
1465to fully restore a clean build.
1466
1467=head1 Internal Changes
1468
1469=over
1470
1471=item *
1472
4263dd11 1473Synonyms for the misleadingly named C<av_len()> have been created:
5ed58cbd
RS
1474C<av_top_index()> and C<av_tindex>. All three of these return the
1475number of the highest index in the array, not the number of elements it
1476contains.
1477
1478=item *
1479
1480SvUPGRADE() is no longer an expression. Originally this macro (and its
1481underlying function, sv_upgrade()) were documented as boolean, although
1482in reality they always croaked on error and never returned false. In 2005
1483the documentation was updated to specify a void return value, but
1484SvUPGRADE() was left always returning 1 for backwards compatibility. This
1485has now been removed, and SvUPGRADE() is now a statement with no return
1486value.
1487
1488So this is now a syntax error:
1489
1490 if (!SvUPGRADE(sv)) { croak(...); }
1491
1492If you have code like that, simply replace it with
1493
1494 SvUPGRADE(sv);
1495
1496or to to avoid compiler warnings with older perls, possibly
1497
1498 (void)SvUPGRADE(sv);
1499
1500=item *
1501
1502Perl has a new copy-on-write mechanism that allows any SvPOK scalar to be
1503upgraded to a copy-on-write scalar. A reference count on the string buffer
d16360cf
RS
1504is stored in the string buffer itself. This feature is B<not enabled by
1505default>.
5ed58cbd 1506
d16360cf
RS
1507It can be enabled in a perl build by running F<Configure> with
1508B<-Accflags=-DPERL_NEW_COPY_ON_WRITE>, and we would encourage XS authors
1509to try their code with such an enabled perl, and provide feedback.
1510Unfortunately, there is not yet a good guide to updating XS code to cope
1511with COW. Until such a document is available, consult the perl5-porters
1512mailing list.
5ed58cbd 1513
d16360cf
RS
1514It breaks a few XS modules by allowing copy-on-write scalars to go
1515through code paths that never encountered them before.
5ed58cbd
RS
1516
1517=item *
1518
1519Copy-on-write no longer uses the SvFAKE and SvREADONLY flags. Hence,
1520SvREADONLY indicates a true read-only SV.
1521
1522Use the SvIsCOW macro (as before) to identify a copy-on-write scalar.
1523
1524=item *
1525
f105b7be 1526C<PL_glob_index> is gone.
5ed58cbd
RS
1527
1528=item *
1529
1530The private Perl_croak_no_modify has had its context parameter removed. It is
1531now has a void prototype. Users of the public API croak_no_modify remain
1532unaffected.
1533
1534=item *
1535
1536Copy-on-write (shared hash key) scalars are no longer marked read-only.
1537C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
1538true.
1539
1540=item *
1541
1542A new op type, C<OP_PADRANGE> has been introduced. The perl peephole
1543optimiser will, where possible, substitute a single padrange op for a
1544pushmark followed by one or more pad ops, and possibly also skipping list
1545and nextstate ops. In addition, the op can carry out the tasks associated
f105b7be 1546with the RHS of a C<< my(...) = @_ >> assignment, so those ops may be optimised
5ed58cbd
RS
1547away too.
1548
1549=item *
1550
1551Case-insensitive matching inside a [bracketed] character class with a
1552multi-character fold no longer excludes one of the possibilities in the
1553circumstances that it used to. [perl #89774].
1554
1555=item *
1556
1557C<PL_formfeed> has been removed.
1558
1559=item *
1560
1561The regular expression engine no longer reads one byte past the end of the
1562target string. While for all internally well-formed scalars this should
1563never have been a problem, this change facilitates clever tricks with
1564string buffers in CPAN modules. [perl #73542]
1565
1566=item *
1567
1568Inside a BEGIN block, C<PL_compcv> now points to the currently-compiling
1569subroutine, rather than the BEGIN block itself.
1570
1571=item *
1572
1573C<mg_length> has been deprecated.
1574
1575=item *
1576
1577C<sv_len> now always returns a byte count and C<sv_len_utf8> a character
1578count. Previously, C<sv_len> and C<sv_len_utf8> were both buggy and would
1579sometimes returns bytes and sometimes characters. C<sv_len_utf8> no longer
be12dd22 1580assumes that its argument is in UTF-8. Neither of these creates UTF-8 caches
5ed58cbd
RS
1581for tied or overloaded values or for non-PVs any more.
1582
1583=item *
1584
1585C<sv_mortalcopy> now copies string buffers of shared hash key scalars when
1586called from XS modules [perl #79824].
1587
1588=item *
1589
1590C<RXf_SPLIT> and C<RXf_SKIPWHITE> are no longer used. They are now
1591#defined as 0.
1592
1593=item *
1594
1595The new C<RXf_MODIFIES_VARS> flag can be set by custom regular expression
1596engines to indicate that the execution of the regular expression may cause
1597variables to be modified. This lets C<s///> know to skip certain
1598optimisations. Perl's own regular expression engine sets this flag for the
1599special backtracking verbs that set $REGMARK and $REGERROR.
1600
1601=item *
1602
1603The APIs for accessing lexical pads have changed considerably.
1604
1605C<PADLIST>s are now longer C<AV>s, but their own type instead.
1606C<PADLIST>s now contain a C<PAD> and a C<PADNAMELIST> of C<PADNAME>s,
1607rather than C<AV>s for the pad and the list of pad names. C<PAD>s,
1608C<PADNAMELIST>s, and C<PADNAME>s are to be accessed as such through the
1609newly added pad API instead of the plain C<AV> and C<SV> APIs. See
1610L<perlapi> for details.
1611
1612=item *
1613
1614In the regex API, the numbered capture callbacks are passed an index
1615indicating what match variable is being accessed. There are special
1616index values for the C<$`, $&, $&> variables. Previously the same three
1617values were used to retrieve C<${^PREMATCH}, ${^MATCH}, ${^POSTMATCH}>
1618too, but these have now been assigned three separate values. See
1619L<perlreapi/Numbered capture callbacks>.
1620
1621=item *
1622
1623C<PL_sawampersand> was previously a boolean indicating that any of
1624C<$`, $&, $&> had been seen; it now contains three one-bit flags
1625indicating the presence of each of the variables individually.
1626
1627=item *
1628
1629The C<CV *> typemap entry now supports C<&{}> overloading and typeglobs,
1630just like C<&{...}> [perl #96872].
1631
1632=item *
1633
1634The C<SVf_AMAGIC> flag to indicate overloading is now on the stash, not the
1635object. It is now set automatically whenever a method or @ISA changes, so
1636its meaning has changed, too. It now means "potentially overloaded". When
1637the overload table is calculated, the flag is automatically turned off if
1638there is no overloading, so there should be no noticeable slowdown.
1639
1640The staleness of the overload tables is now checked when overload methods
1641are invoked, rather than during C<bless>.
1642
1643"A" magic is gone. The changes to the handling of the C<SVf_AMAGIC> flag
1644eliminate the need for it.
1645
1646C<PL_amagic_generation> has been removed as no longer necessary. For XS
1647modules, it is now a macro alias to C<PL_na>.
1648
1649The fallback overload setting is now stored in a stash entry separate from
1650overloadedness itself.
1651
1652=item *
1653
1654The character-processing code has been cleaned up in places. The changes
1655should be operationally invisible.
1656
1657=item *
1658
e612b5a0 1659The C<study> function was made a no-op in v5.16. It was simply disabled via
5ed58cbd
RS
1660a C<return> statement; the code was left in place. Now the code supporting
1661what C<study> used to do has been removed.
1662
1663=item *
1664
1665Under threaded perls, there is no longer a separate PV allocated for every
1666COP to store its package name (C<< cop->stashpv >>). Instead, there is an
1667offset (C<< cop->stashoff >>) into the new C<PL_stashpad> array, which
1668holds stash pointers.
1669
1670=item *
1671
1672In the pluggable regex API, the C<regexp_engine> struct has acquired a new
1673field C<op_comp>, which is currently just for perl's internal use, and
f105b7be 1674should be initialized to NULL by other regex plugin modules.
5ed58cbd
RS
1675
1676=item *
1677
7779650e 1678A new function C<alloccopstash> has been added to the API, but is considered
5ed58cbd
RS
1679experimental. See L<perlapi>.
1680
1681=item *
1682
1683Perl used to implement get magic in a way that would sometimes hide bugs in
4263dd11 1684code that could call mg_get() too many times on magical values. This hiding of
5ed58cbd
RS
1685errors no longer occurs, so long-standing bugs may become visible now. If
1686you see magic-related errors in XS code, check to make sure it, together
1687with the Perl API functions it uses, calls mg_get() only once on SvGMAGICAL()
1688values.
1689
1690=item *
1691
1692OP allocation for CVs now uses a slab allocator. This simplifies
1693memory management for OPs allocated to a CV, so cleaning up after a
1694compilation error is simpler and safer [perl #111462][perl #112312].
1695
1696=item *
1697
f105b7be 1698C<PERL_DEBUG_READONLY_OPS> has been rewritten to work with the new slab
5ed58cbd
RS
1699allocator, allowing it to catch more violations than before.
1700
1701=item *
1702
f105b7be
KE
1703The old slab allocator for ops, which was only enabled for C<PERL_IMPLICIT_SYS>
1704and C<PERL_DEBUG_READONLY_OPS>, has been retired.
5ed58cbd
RS
1705
1706=back
1707
1708=head1 Selected Bug Fixes
1709
1710=over 4
1711
1712=item *
1713
1714Here-doc terminators no longer require a terminating newline character when
1715they occur at the end of a file. This was already the case at the end of a
1716string eval [perl #65838].
1717
1718=item *
1719
f105b7be 1720C<-DPERL_GLOBAL_STRUCT> builds now free the global struct B<after>
5ed58cbd
RS
1721they've finished using it.
1722
1723=item *
1724
1725A trailing '/' on a path in @INC will no longer have an additional '/'
1726appended.
1727
1728=item *
1729
1730The C<:crlf> layer now works when unread data doesn't fit into its own
1731buffer. [perl #112244].
1732
1733=item *
1734
1735C<ungetc()> now handles UTF-8 encoded data. [perl #116322].
1736
1737=item *
1738
1739A bug in the core typemap caused any C types that map to the T_BOOL core
1740typemap entry to not be set, updated, or modified when the T_BOOL variable was
1741used in an OUTPUT: section with an exception for RETVAL. T_BOOL in an INPUT:
1742section was not affected. Using a T_BOOL return type for an XSUB (RETVAL)
1743was not affected. A side effect of fixing this bug is, if a T_BOOL is specified
1744in the OUTPUT: section (which previous did nothing to the SV), and a read only
1745SV (literal) is passed to the XSUB, croaks like "Modification of a read-only
1746value attempted" will happen. [perl #115796]
1747
1748=item *
1749
1750On many platforms, providing a directory name as the script name caused perl
1751to do nothing and report success. It should now universally report an error
1752and exit nonzero. [perl #61362]
1753
1754=item *
1755
1756C<sort {undef} ...> under fatal warnings no longer crashes. It had
e612b5a0 1757begun crashing in Perl v5.16.
5ed58cbd
RS
1758
1759=item *
1760
1761Stashes blessed into each other
1762(C<bless \%Foo::, 'Bar'; bless \%Bar::, 'Foo'>) no longer result in double
e612b5a0 1763frees. This bug started happening in Perl v5.16.
5ed58cbd
RS
1764
1765=item *
1766
1767Numerous memory leaks have been fixed, mostly involving fatal warnings and
1768syntax errors.
1769
1770=item *
1771
1772Some failed regular expression matches such as C<'f' =~ /../g> were not
1773resetting C<pos>. Also, "match-once" patterns (C<m?...?g>) failed to reset
1774it, too, when invoked a second time [perl #23180].
1775
1776=item *
1777
1778Accessing C<$&> after a pattern match now works if it had not been seen
1779before the match. I.e., this applies to C<${'&'}> (under C<no strict>) and
1780C<eval '$&'>. The same applies to C<$'> and C<$`> [perl #4289].
1781
1782=item *
1783
1784Several bugs involving C<local *ISA> and C<local *Foo::> causing stale
1785MRO caches have been fixed.
1786
1787=item *
1788
1789Defining a subroutine when its typeglob has been aliased no longer results
e612b5a0 1790in stale method caches. This bug was introduced in Perl v5.10.
5ed58cbd
RS
1791
1792=item *
1793
1794Localising a typeglob containing a subroutine when the typeglob's package
1795has been deleted from its parent stash no longer produces an error. This
e612b5a0 1796bug was introduced in Perl v5.14.
5ed58cbd
RS
1797
1798=item *
1799
1800Under some circumstances, C<local *method=...> would fail to reset method
1801caches upon scope exit.
1802
1803=item *
1804
1805C</[.foo.]/> is no longer an error, but produces a warning (as before) and
1806is treated as C</[.fo]/> [perl #115818].
1807
1808=item *
1809
1810C<goto $tied_var> now calls FETCH before deciding what type of goto
1811(subroutine or label) this is.
1812
1813=item *
1814
1815Renaming packages through glob assignment
1816(C<*Foo:: = *Bar::; *Bar:: = *Baz::>) in combination with C<m?...?> and
1817C<reset> no longer makes threaded builds crash.
1818
1819=item *
1820
1821A number of bugs related to assigning a list to hash have been fixed. Many of
1822these involve lists with repeated keys like C<(1, 1, 1, 1)>.
1823
1824=over 4
1825
1826=item *
1827
1828The expression C<scalar(%h = (1, 1, 1, 1))> now returns C<4>, not C<2>.
1829
1830=item *
1831
1832The return value of C<%h = (1, 1, 1)> in list context was wrong. Previously
1833this would return C<(1, undef, 1)>, now it returns C<(1, undef)>.
1834
1835=item *
1836
1837Perl now issues the same warning on C<($s, %h) = (1, {})> as it does for
1838C<(%h) = ({})>, "Reference found where even-sized list expected".
1839
1840=item *
1841
1842A number of additional edge cases in list assignment to hashes were
1843corrected. For more details see commit 23b7025ebc.
1844
1845=back
1846
1847=item *
1848
1849Attributes applied to lexical variables no longer leak memory.
1850[perl #114764]
1851
1852=item *
1853
1854C<dump>, C<goto>, C<last>, C<next>, C<redo> or C<require> followed by a
1855bareword (or version) and then an infix operator is no longer a syntax
1856error. It used to be for those infix operators (like C<+>) that have a
1857different meaning where a term is expected. [perl #105924]
1858
1859=item *
1860
1861C<require a::b . 1> and C<require a::b + 1> no longer produce erroneous
1862ambiguity warnings. [perl #107002]
1863
1864=item *
1865
1866Class method calls are now allowed on any string, and not just strings
1867beginning with an alphanumeric character. [perl #105922]
1868
1869=item *
1870
1871An empty pattern created with C<qr//> used in C<m///> no longer triggers
1872the "empty pattern reuses last pattern" behaviour. [perl #96230]
1873
1874=item *
1875
1876Tying a hash during iteration no longer results in a memory leak.
1877
1878=item *
1879
1880Freeing a tied hash during iteration no longer results in a memory leak.
1881
1882=item *
1883
1884List assignment to a tied array or hash that dies on STORE no longer
1885results in a memory leak.
1886
1887=item *
1888
1889If the hint hash (C<%^H>) is tied, compile-time scope entry (which copies
1890the hint hash) no longer leaks memory if FETCH dies. [perl #107000]
1891
1892=item *
1893
1894Constant folding no longer inappropriately triggers the special
1895C<split " "> behaviour. [perl #94490]
1896
1897=item *
1898
1899C<defined scalar(@array)>, C<defined do { &foo }>, and similar constructs
1900now treat the argument to C<defined> as a simple scalar. [perl #97466]
1901
1902=item *
1903
1904Running a custom debugging that defines no C<*DB::DB> glob or provides a
1905subroutine stub for C<&DB::DB> no longer results in a crash, but an error
1906instead. [perl #114990]
1907
1908=item *
1909
1910C<reset ""> now matches its documentation. C<reset> only resets C<m?...?>
1911patterns when called with no argument. An empty string for an argument now
1912does nothing. (It used to be treated as no argument.) [perl #97958]
1913
1914=item *
1915
1916C<printf> with an argument returning an empty list no longer reads past the
1917end of the stack, resulting in erratic behaviour. [perl #77094]
1918
1919=item *
1920
1921C<--subname> no longer produces erroneous ambiguity warnings.
1922[perl #77240]
1923
1924=item *
1925
1926C<v10> is now allowed as a label or package name. This was inadvertently
e612b5a0 1927broken when v-strings were added in Perl v5.6. [perl #56880]
5ed58cbd
RS
1928
1929=item *
1930
1931C<length>, C<pos>, C<substr> and C<sprintf> could be confused by ties,
1932overloading, references and typeglobs if the stringification of such
be12dd22 1933changed the internal representation to or from UTF-8. [perl #114410]
5ed58cbd
RS
1934
1935=item *
1936
1937utf8::encode now calls FETCH and STORE on tied variables. utf8::decode now
1938calls STORE (it was already calling FETCH).
1939
1940=item *
1941
1942C<$tied =~ s/$non_utf8/$utf8/> no longer loops infinitely if the tied
1943variable returns a Latin-1 string, shared hash key scalar, or reference or
2ae351f8 1944typeglob that stringifies as ASCII or Latin-1. This was a regression from
e612b5a0 1945v5.12.
5ed58cbd
RS
1946
1947=item *
1948
1949C<s///> without /e is now better at detecting when it needs to forego
1950certain optimisations, fixing some buggy cases:
1951
1952=over
1953
1954=item *
1955
1956Match variables in certain constructs (C<&&>, C<||>, C<..> and others) in
1957the replacement part; e.g., C<s/(.)/$l{$a||$1}/g>. [perl #26986]
1958
1959=item *
1960
1961Aliases to match variables in the replacement.
1962
1963=item *
1964
1965C<$REGERROR> or C<$REGMARK> in the replacement. [perl #49190]
1966
1967=item *
1968
1969An empty pattern (C<s//$foo/>) that causes the last-successful pattern to
1970be used, when that pattern contains code blocks that modify the variables
1971in the replacement.
1972
1973=back
1974
1975=item *
1976
1977The taintedness of the replacement string no longer affects the taintedness
1978of the return value of C<s///e>.
1979
1980=item *
1981
1982The C<$|> autoflush variable is created on-the-fly when needed. If this
1983happened (e.g., if it was mentioned in a module or eval) when the
1984currently-selected filehandle was a typeglob with an empty IO slot, it used
1985to crash. [perl #115206]
1986
1987=item *
1988
1989Line numbers at the end of a string eval are no longer off by one.
1990[perl #114658]
1991
1992=item *
1993
1994@INC filters (subroutines returned by subroutines in @INC) that set $_ to a
1995copy-on-write scalar no longer cause the parser to modify that string
1996buffer in place.
1997
1998=item *
1999
2000C<length($object)> no longer returns the undefined value if the object has
2001string overloading that returns undef. [perl #115260]
2002
2003=item *
2004
2005The use of C<PL_stashcache>, the stash name lookup cache for method calls, has
2006been restored,
2007
2008Commit da6b625f78f5f133 in August 2011 inadvertently broke the code that looks
2009up values in C<PL_stashcache>. As it's a only cache, quite correctly everything
2010carried on working without it.
2011
2012=item *
2013
e612b5a0 2014The error "Can't localize through a reference" had disappeared in v5.16.0
5ed58cbd 2015when C<local %$ref> appeared on the last line of an lvalue subroutine.
e612b5a0 2016This error disappeared for C<\local %$ref> in perl v5.8.1. It has now
5ed58cbd
RS
2017been restored.
2018
2019=item *
2020
2021The parsing of here-docs has been improved significantly, fixing several
2022parsing bugs and crashes and one memory leak, and correcting wrong
2023subsequent line numbers under certain conditions.
2024
2025=item *
2026
2027Inside an eval, the error message for an unterminated here-doc no longer
2028has a newline in the middle of it [perl #70836].
2029
2030=item *
2031
2032A substitution inside a substitution pattern (C<s/${s|||}//>) no longer
2033confuses the parser.
2034
2035=item *
2036
2037It may be an odd place to allow comments, but C<s//"" # hello/e> has
2038always worked, I<unless> there happens to be a null character before the
2039first #. Now it works even in the presence of nulls.
2040
2041=item *
2042
2043An invalid range in C<tr///> or C<y///> no longer results in a memory leak.
2044
2045=item *
2046
2047String eval no longer treats a semicolon-delimited quote-like operator at
2048the very end (C<eval 'q;;'>) as a syntax error.
2049
2050=item *
2051
2052C<< warn {$_ => 1} + 1 >> is no longer a syntax error. The parser used to
2053get confused with certain list operators followed by an anonymous hash and
2054then an infix operator that shares its form with a unary operator.
2055
2056=item *
2057
2058C<(caller $n)[6]> (which gives the text of the eval) used to return the
2059actual parser buffer. Modifying it could result in crashes. Now it always
2060returns a copy. The string returned no longer has "\n;" tacked on to the
2061end. The returned text also includes here-doc bodies, which used to be
2062omitted.
2063
2064=item *
2065
be12dd22
RS
2066Reset the UTF-8 position cache when accessing magical variables to avoid the
2067string buffer and the UTF-8 position cache getting out of sync
5ed58cbd
RS
2068[perl #114410].
2069
2070=item *
2071
be12dd22
RS
2072Various cases of get magic being called twice for magical UTF-8
2073strings have been fixed.
5ed58cbd
RS
2074
2075=item *
2076
2077This code (when not in the presence of C<$&> etc)
2078
2079 $_ = 'x' x 1_000_000;
2080 1 while /(.)/;
2081
2082used to skip the buffer copy for performance reasons, but suffered from C<$1>
2083etc changing if the original string changed. That's now been fixed.
2084
2085=item *
2086
2087Perl doesn't use PerlIO anymore to report out of memory messages, as PerlIO
2088might attempt to allocate more memory.
2089
2090=item *
2091
2092In a regular expression, if something is quantified with C<{n,m}> where
2093C<S<n E<gt> m>>, it can't possibly match. Previously this was a fatal
2094error, but now is merely a warning (and that something won't match).
2095[perl #82954].
2096
2097=item *
2098
2099It used to be possible for formats defined in subroutines that have
2100subsequently been undefined and redefined to close over variables in the
2101wrong pad (the newly-defined enclosing sub), resulting in crashes or
2102"Bizarre copy" errors.
2103
2104=item *
2105
2106Redefinition of XSUBs at run time could produce warnings with the wrong
2107line number.
2108
2109=item *
2110
2111The %vd sprintf format does not support version objects for alpha versions.
2112It used to output the format itself (%vd) when passed an alpha version, and
2113also emit an "Invalid conversion in printf" warning. It no longer does,
2114but produces the empty string in the output. It also no longer leaks
2115memory in this case.
2116
2117=item *
2118
2119C<< $obj->SUPER::method >> calls in the main package could fail if the
2120SUPER package had already been accessed by other means.
2121
2122=item *
2123
f105b7be 2124Stash aliasing (C<< *foo:: = *bar:: >>) no longer causes SUPER calls to ignore
5ed58cbd
RS
2125changes to methods or @ISA or use the wrong package.
2126
2127=item *
2128
2129Method calls on packages whose names end in ::SUPER are no longer treated
2130as SUPER method calls, resulting in failure to find the method.
2131Furthermore, defining subroutines in such packages no longer causes them to
2132be found by SUPER method calls on the containing package [perl #114924].
2133
2134=item *
2135
2136C<\w> now matches the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D
2137(ZERO WIDTH JOINER). C<\W> no longer matches these. This change is because
2138Unicode corrected their definition of what C<\w> should match.
2139
2140=item *
2141
2142C<dump LABEL> no longer leaks its label.
2143
2144=item *
2145
2146Constant folding no longer changes the behaviour of functions like C<stat()>
2147and C<truncate()> that can take either filenames or handles.
2148C<stat 1 ? foo : bar> nows treats its argument as a file name (since it is an
2149arbitrary expression), rather than the handle "foo".
2150
2151=item *
2152
2153C<truncate FOO, $len> no longer falls back to treating "FOO" as a file name if
e612b5a0 2154the filehandle has been deleted. This was broken in Perl v5.16.0.
5ed58cbd
RS
2155
2156=item *
2157
2158Subroutine redefinitions after sub-to-glob and glob-to-glob assignments no
2159longer cause double frees or panic messages.
2160
2161=item *
2162
2163C<s///> now turns vstrings into plain strings when performing a substitution,
2164even if the resulting string is the same (C<s/a/a/>).
2165
2166=item *
2167
2168Prototype mismatch warnings no longer erroneously treat constant subs as having
2169no prototype when they actually have "".
2170
2171=item *
2172
2173Constant subroutines and forward declarations no longer prevent prototype
2174mismatch warnings from omitting the sub name.
2175
2176=item *
2177
2178C<undef> on a subroutine now clears call checkers.
2179
2180=item *
2181
e612b5a0 2182The C<ref> operator started leaking memory on blessed objects in Perl v5.16.0.
5ed58cbd
RS
2183This has been fixed [perl #114340].
2184
2185=item *
2186
2187C<use> no longer tries to parse its arguments as a statement, making
2188C<use constant { () };> a syntax error [perl #114222].
2189
2190=item *
2191
2192On debugging builds, "uninitialized" warnings inside formats no longer cause
2193assertion failures.
2194
2195=item *
2196
2197On debugging builds, subroutines nested inside formats no longer cause
2198assertion failures [perl #78550].
2199
2200=item *
2201
2202Formats and C<use> statements are now permitted inside formats.
2203
2204=item *
2205
2206C<print $x> and C<sub { print $x }-E<gt>()> now always produce the same output.
2207It was possible for the latter to refuse to close over $x if the variable was
2208not active; e.g., if it was defined outside a currently-running named
2209subroutine.
2210
2211=item *
2212
2213Similarly, C<print $x> and C<print eval '$x'> now produce the same output.
2214This also allows "my $x if 0" variables to be seen in the debugger [perl
2215#114018].
2216
2217=item *
2218
2219Formats called recursively no longer stomp on their own lexical variables, but
2220each recursive call has its own set of lexicals.
2221
2222=item *
2223
2224Attempting to free an active format or the handle associated with it no longer
2225results in a crash.
2226
2227=item *
2228
2229Format parsing no longer gets confused by braces, semicolons and low-precedence
2230operators. It used to be possible to use braces as format delimiters (instead
2231of C<=> and C<.>), but only sometimes. Semicolons and low-precedence operators
2232in format argument lines no longer confuse the parser into ignoring the line's
2233return value. In format argument lines, braces can now be used for anonymous
2234hashes, instead of being treated always as C<do> blocks.
2235
2236=item *
2237
2238Formats can now be nested inside code blocks in regular expressions and other
2239quoted constructs (C</(?{...})/> and C<qq/${...}/>) [perl #114040].
2240
2241=item *
2242
2243Formats are no longer created after compilation errors.
2244
2245=item *
2246
2247Under debugging builds, the B<-DA> command line option started crashing in Perl
e612b5a0 2248v5.16.0. It has been fixed [perl #114368].
5ed58cbd
RS
2249
2250=item *
2251
2252A potential deadlock scenario involving the premature termination of a pseudo-
2253forked child in a Windows build with ithreads enabled has been fixed. This
2254resolves the common problem of the F<t/op/fork.t> test hanging on Windows [perl
2255#88840].
2256
2257=item *
2258
5ed58cbd
RS
2259The code which generates errors from C<require()> could potentially read one or
2260two bytes before the start of the filename for filenames less than three bytes
2261long and ending C</\.p?\z/>. This has now been fixed. Note that it could
2262never have happened with module names given to C<use()> or C<require()> anyway.
2263
2264=item *
2265
2266The handling of pathnames of modules given to C<require()> has been made
2267thread-safe on VMS.
2268
2269=item *
2270
d85cd26b
RS
2271Non-blocking sockets have been fixed on VMS.
2272
2273=item *
2274
5ed58cbd
RS
2275A bug in the compilation of a C</(?{})/> expression which affected the TryCatch
2276test suite has been fixed [perl #114242].
2277
2278=item *
2279
2280Pod can now be nested in code inside a quoted construct outside of a string
2281eval. This used to work only within string evals [perl #114040].
2282
2283=item *
2284
2285C<goto ''> now looks for an empty label, producing the "goto must have
2286label" error message, instead of exiting the program [perl #111794].
2287
2288=item *
2289
2290C<goto "\0"> now dies with "Can't find label" instead of "goto must have
2291label".
2292
2293=item *
2294
2295The C function C<hv_store> used to result in crashes when used on C<%^H>
2296[perl #111000].
2297
2298=item *
2299
2300A call checker attached to a closure prototype via C<cv_set_call_checker>
2301is now copied to closures cloned from it. So C<cv_set_call_checker> now
2302works inside an attribute handler for a closure.
2303
2304=item *
2305
2306Writing to C<$^N> used to have no effect. Now it croaks with "Modification
2307of a read-only value" by default, but that can be overridden by a custom
2308regular expression engine, as with C<$1> [perl #112184].
2309
2310=item *
2311
2312C<undef> on a control character glob (C<undef *^H>) no longer emits an
2313erroneous warning about ambiguity [perl #112456].
2314
2315=item *
2316
2317For efficiency's sake, many operators and built-in functions return the
2318same scalar each time. Lvalue subroutines and subroutines in the CORE::
2319namespace were allowing this implementation detail to leak through.
2320C<print &CORE::uc("a"), &CORE::uc("b")> used to print "BB". The same thing
2321would happen with an lvalue subroutine returning the return value of C<uc>.
2322Now the value is copied in such cases.
2323
2324=item *
2325
2326C<method {}> syntax with an empty block or a block returning an empty list
2327used to crash or use some random value left on the stack as its invocant.
2328Now it produces an error.
2329
2330=item *
2331
2332C<vec> now works with extremely large offsets (E<gt>2 GB) [perl #111730].
2333
2334=item *
2335
2336Changes to overload settings now take effect immediately, as do changes to
2337inheritance that affect overloading. They used to take effect only after
2338C<bless>.
2339
2340Objects that were created before a class had any overloading used to remain
2341non-overloaded even if the class gained overloading through C<use overload>
2342or @ISA changes, and even after C<bless>. This has been fixed
2343[perl #112708].
2344
2345=item *
2346
2347Classes with overloading can now inherit fallback values.
2348
2349=item *
2350
2351Overloading was not respecting a fallback value of 0 if there were
2352overloaded objects on both sides of an assignment operator like C<+=>
2353[perl #111856].
2354
2355=item *
2356
2357C<pos> now croaks with hash and array arguments, instead of producing
2358erroneous warnings.
2359
2360=item *
2361
2362C<while(each %h)> now implies C<while(defined($_ = each %h))>, like
2363C<readline> and C<readdir>.
2364
2365=item *
2366
2367Subs in the CORE:: namespace no longer crash after C<undef *_> when called
2368with no argument list (C<&CORE::time> with no parentheses).
2369
2370=item *
2371
2372C<unpack> no longer produces the "'/' must follow a numeric type in unpack"
2373error when it is the data that are at fault [perl #60204].
2374
2375=item *
2376
2377C<join> and C<"@array"> now call FETCH only once on a tied C<$">
2378[perl #8931].
2379
2380=item *
2381
2382Some subroutine calls generated by compiling core ops affected by a
2383C<CORE::GLOBAL> override had op checking performed twice. The checking
2384is always idempotent for pure Perl code, but the double checking can
2385matter when custom call checkers are involved.
2386
2387=item *
2388
2389A race condition used to exist around fork that could cause a signal sent to
2390the parent to be handled by both parent and child. Signals are now blocked
2391briefly around fork to prevent this from happening [perl #82580].
2392
2393=item *
2394
2395The implementation of code blocks in regular expressions, such as C<(?{})>
2396and C<(??{})>, has been heavily reworked to eliminate a whole slew of bugs.
2397The main user-visible changes are:
2398
2399=over 4
2400
2401=item *
2402
2403Code blocks within patterns are now parsed in the same pass as the
2404surrounding code; in particular it is no longer necessary to have balanced
2405braces: this now works:
2406
2407 /(?{ $x='{' })/
2408
2409This means that this error message is no longer generated:
2410
2411 Sequence (?{...}) not terminated or not {}-balanced in regex
2412
2413but a new error may be seen:
2414
2415 Sequence (?{...}) not terminated with ')'
2416
2417In addition, literal code blocks within run-time patterns are only
2418compiled once, at perl compile-time:
2419
2420 for my $p (...) {
2421 # this 'FOO' block of code is compiled once,
2422 # at the same time as the surrounding 'for' loop
2423 /$p{(?{FOO;})/;
2424 }
2425
2426=item *
2427
2428Lexical variables are now sane as regards scope, recursion and closure
2429behavior. In particular, C</A(?{B})C/> behaves (from a closure viewpoint)
2430exactly like C</A/ && do { B } && /C/>, while C<qr/A(?{B})C/> is like
2431C<sub {/A/ && do { B } && /C/}>. So this code now works how you might
2432expect, creating three regexes that match 0, 1, and 2:
2433
2434 for my $i (0..2) {
2435 push @r, qr/^(??{$i})$/;
2436 }
2437 "1" =~ $r[1]; # matches
2438
2439=item *
2440
2441The C<use re 'eval'> pragma is now only required for code blocks defined
2442at runtime; in particular in the following, the text of the C<$r> pattern is
2443still interpolated into the new pattern and recompiled, but the individual
2444compiled code-blocks within C<$r> are reused rather than being recompiled,
2445and C<use re 'eval'> isn't needed any more:
2446
2447 my $r = qr/abc(?{....})def/;
2448 /xyz$r/;
2449
2450=item *
2451
2452Flow control operators no longer crash. Each code block runs in a new
2453dynamic scope, so C<next> etc. will not see
2454any enclosing loops. C<return> returns a value
2455from the code block, not from any enclosing subroutine.
2456
2457=item *
2458
2459Perl normally caches the compilation of run-time patterns, and doesn't
2460recompile if the pattern hasn't changed, but this is now disabled if
2461required for the correct behavior of closures. For example:
2462
2463 my $code = '(??{$x})';
2464 for my $x (1..3) {
2465 # recompile to see fresh value of $x each time
2466 $x =~ /$code/;
2467 }
2468
2469=item *
2470
2471The C</msix> and C<(?msix)> etc. flags are now propagated into the return
2472value from C<(??{})>; this now works:
2473
2474 "AB" =~ /a(??{'b'})/i;
2475
2476=item *
2477
2478Warnings and errors will appear to come from the surrounding code (or for
2479run-time code blocks, from an eval) rather than from an C<re_eval>:
2480
2481 use re 'eval'; $c = '(?{ warn "foo" })'; /$c/;
2482 /(?{ warn "foo" })/;
2483
2484formerly gave:
2485
2486 foo at (re_eval 1) line 1.
2487 foo at (re_eval 2) line 1.
2488
2489and now gives:
2490
2491 foo at (eval 1) line 1.
2492 foo at /some/prog line 2.
2493
2494=back
2495
2496=item *
2497
2e7bc647
KW
2498Perl now can be recompiled to use any Unicode version. In v5.16, it
2499worked on Unicodes 6.0 and 6.1, but there were various bugs if earlier
2500releases were used; the older the release the more problems.
5ed58cbd
RS
2501
2502=item *
2503
2504C<vec> no longer produces "uninitialized" warnings in lvalue context
2505[perl #9423].
2506
2507=item *
2508
2509An optimization involving fixed strings in regular expressions could cause
2510a severe performance penalty in edge cases. This has been fixed
2511[perl #76546].
2512
2513=item *
2514
2515In certain cases, including empty subpatterns within a regular expression (such
2516as C<(?:)> or C<(?:|)>) could disable some optimizations. This has been fixed.
2517
2518=item *
2519
2520The "Can't find an opnumber" message that C<prototype> produces when passed
2521a string like "CORE::nonexistent_keyword" now passes UTF-8 and embedded
2522NULs through unchanged [perl #97478].
2523
2524=item *
2525
2526C<prototype> now treats magical variables like C<$1> the same way as
2527non-magical variables when checking for the CORE:: prefix, instead of
2528treating them as subroutine names.
2529
2530=item *
2531
2532Under threaded perls, a runtime code block in a regular expression could
2533corrupt the package name stored in the op tree, resulting in bad reads
2534in C<caller>, and possibly crashes [perl #113060].
2535
2536=item *
2537
2538Referencing a closure prototype (C<\&{$_[1]}> in an attribute handler for a
2539closure) no longer results in a copy of the subroutine (or assertion
2540failures on debugging builds).
2541
2542=item *
2543
2544C<eval '__PACKAGE__'> now returns the right answer on threaded builds if
2545the current package has been assigned over (as in
2546C<*ThisPackage:: = *ThatPackage::>) [perl #78742].
2547
2548=item *
2549
2550If a package is deleted by code that it calls, it is possible for C<caller>
2551to see a stack frame belonging to that deleted package. C<caller> could
2552crash if the stash's memory address was reused for a scalar and a
2553substitution was performed on the same scalar [perl #113486].
2554
2555=item *
2556
2557C<UNIVERSAL::can> no longer treats its first argument differently
2558depending on whether it is a string or number internally.
2559
2560=item *
2561
2562C<open> with C<< <& >> for the mode checks to see whether the third argument is
2563a number, in determining whether to treat it as a file descriptor or a handle
2564name. Magical variables like C<$1> were always failing the numeric check and
2565being treated as handle names.
2566
2567=item *
2568
2569C<warn>'s handling of magical variables (C<$1>, ties) has undergone several
2570fixes. C<FETCH> is only called once now on a tied argument or a tied C<$@>
2571[perl #97480]. Tied variables returning objects that stringify as "" are
2572no longer ignored. A tied C<$@> that happened to return a reference the
2573I<previous> time it was used is no longer ignored.
2574
2575=item *
2576
2577C<warn ""> now treats C<$@> with a number in it the same way, regardless of
2578whether it happened via C<$@=3> or C<$@="3">. It used to ignore the
2579former. Now it appends "\t...caught", as it has always done with
2580C<$@="3">.
2581
2582=item *
2583
2584Numeric operators on magical variables (e.g., S<C<$1 + 1>>) used to use
2585floating point operations even where integer operations were more appropriate,
2586resulting in loss of accuracy on 64-bit platforms [perl #109542].
2587
2588=item *
2589
2590Unary negation no longer treats a string as a number if the string happened
2591to be used as a number at some point. So, if C<$x> contains the string "dogs",
2592C<-$x> returns "-dogs" even if C<$y=0+$x> has happened at some point.
2593
2594=item *
2595
e612b5a0 2596In Perl v5.14, C<-'-10'> was fixed to return "10", not "+10". But magical
5ed58cbd
RS
2597variables (C<$1>, ties) were not fixed till now [perl #57706].
2598
2599=item *
2600
2601Unary negation now treats strings consistently, regardless of the internal
2602C<UTF8> flag.
2603
2604=item *
2605
2606A regression introduced in Perl v5.16.0 involving
2607C<tr/I<SEARCHLIST>/I<REPLACEMENTLIST>/> has been fixed. Only the first
2608instance is supposed to be meaningful if a character appears more than
2609once in C<I<SEARCHLIST>>. Under some circumstances, the final instance
2610was overriding all earlier ones. [perl #113584]
2611
2612=item *
2613
2614Regular expressions like C<qr/\87/> previously silently inserted a NUL
2615character, thus matching as if it had been written C<qr/\00087/>. Now it
2616matches as if it had been written as C<qr/87/>, with a message that the
2617sequence C<"\8"> is unrecognized.
2618
2619=item *
2620
2621C<__SUB__> now works in special blocks (C<BEGIN>, C<END>, etc.).
2622
2623=item *
2624
2625Thread creation on Windows could theoretically result in a crash if done
2626inside a C<BEGIN> block. It still does not work properly, but it no longer
2627crashes [perl #111610].
2628
2629=item *
2630
2631C<\&{''}> (with the empty string) now autovivifies a stub like any other
2632sub name, and no longer produces the "Unable to create sub" error
2633[perl #94476].
2634
2635=item *
2636
2637A regression introduced in v5.14.0 has been fixed, in which some calls
2638to the C<re> module would clobber C<$_> [perl #113750].
2639
2640=item *
2641
2642C<do FILE> now always either sets or clears C<$@>, even when the file can't be
2643read. This ensures that testing C<$@> first (as recommended by the
2644documentation) always returns the correct result.
2645
2646=item *
2647
2648The array iterator used for the C<each @array> construct is now correctly
2649reset when C<@array> is cleared (RT #75596). This happens for example when the
2650array is globally assigned to, as in C<@array = (...)>, but not when its
2651B<values> are assigned to. In terms of the XS API, it means that C<av_clear()>
2652will now reset the iterator.
2653
2654This mirrors the behaviour of the hash iterator when the hash is cleared.
2655
2656=item *
2657
2658C<< $class->can >>, C<< $class->isa >>, and C<< $class->DOES >> now return
2659correct results, regardless of whether that package referred to by C<$class>
2660exists [perl #47113].
2661
2662=item *
2663
2664Arriving signals no longer clear C<$@> [perl #45173].
2665
2666=item *
2667
2668Allow C<my ()> declarations with an empty variable list [perl #113554].
2669
2670=item *
2671
2672During parsing, subs declared after errors no longer leave stubs
2673[perl #113712].
2674
2675=item *
2676
2677Closures containing no string evals no longer hang on to their containing
2678subroutines, allowing variables closed over by outer subroutines to be
2679freed when the outer sub is freed, even if the inner sub still exists
2680[perl #89544].
2681
2682=item *
2683
2684Duplication of in-memory filehandles by opening with a "<&=" or ">&=" mode
e612b5a0 2685stopped working properly in v5.16.0. It was causing the new handle to
5ed58cbd
RS
2686reference a different scalar variable. This has been fixed [perl #113764].
2687
2688=item *
2689
2690C<qr//> expressions no longer crash with custom regular expression engines
2691that do not set C<offs> at regular expression compilation time
2692[perl #112962].
2693
2694=item *
2695
2696C<delete local> no longer crashes with certain magical arrays and hashes
2697[perl #112966].
2698
2699=item *
2700
2701C<local> on elements of certain magical arrays and hashes used not to
2702arrange to have the element deleted on scope exit, even if the element did
2703not exist before C<local>.
2704
2705=item *
2706
2707C<scalar(write)> no longer returns multiple items [perl #73690].
2708
2709=item *
2710
2711String to floating point conversions no longer misparse certain strings under
2712C<use locale> [perl #109318].
2713
2714=item *
2715
2716C<@INC> filters that die no longer leak memory [perl #92252].
2717
2718=item *
2719
2720The implementations of overloaded operations are now called in the correct
2721context. This allows, among other things, being able to properly override
2722C<< <> >> [perl #47119].
2723
2724=item *
2725
2726Specifying only the C<fallback> key when calling C<use overload> now behaves
2727properly [perl #113010].
2728
2729=item *
2730
2731C<< sub foo { my $a = 0; while ($a) { ... } } >> and
2732C<< sub foo { while (0) { ... } } >> now return the same thing [perl #73618].
2733
2734=item *
2735
2736String negation now behaves the same under C<use integer;> as it does
2737without [perl #113012].
2738
2739=item *
2740
2741C<chr> now returns the Unicode replacement character (U+FFFD) for -1,
2742regardless of the internal representation. -1 used to wrap if the argument
2743was tied or a string internally.
2744
2745=item *
2746
2747Using a C<format> after its enclosing sub was freed could crash as of
e612b5a0 2748perl v5.12.0, if the format referenced lexical variables from the outer sub.
5ed58cbd
RS
2749
2750=item *
2751
2752Using a C<format> after its enclosing sub was undefined could crash as of
e612b5a0 2753perl v5.10.0, if the format referenced lexical variables from the outer sub.
5ed58cbd
RS
2754
2755=item *
2756
2757Using a C<format> defined inside a closure, which format references
2758lexical variables from outside, never really worked unless the C<write>
e612b5a0 2759call was directly inside the closure. In v5.10.0 it even started crashing.
5ed58cbd
RS
2760Now the copy of that closure nearest the top of the call stack is used to
2761find those variables.
2762
2763=item *
2764
2765Formats that close over variables in special blocks no longer crash if a
2766stub exists with the same name as the special block before the special
2767block is compiled.
2768
2769=item *
2770
2771The parser no longer gets confused, treating C<eval foo ()> as a syntax
2772error if preceded by C<print;> [perl #16249].
2773
2774=item *
2775
2776The return value of C<syscall> is no longer truncated on 64-bit platforms
2777[perl #113980].
2778
2779=item *
2780
2781Constant folding no longer causes C<print 1 ? FOO : BAR> to print to the
2782FOO handle [perl #78064].
2783
2784=item *
2785
2786C<do subname> now calls the named subroutine and uses the file name it
2787returns, instead of opening a file named "subname".
2788
2789=item *
2790
2791Subroutines looked up by rv2cv check hooks (registered by XS modules) are
2792now taken into consideration when determining whether C<foo bar> should be
2793the sub call C<foo(bar)> or the method call C<< "bar"->foo >>.
2794
2795=item *
2796
2797C<CORE::foo::bar> is no longer treated specially, allowing global overrides
2798to be called directly via C<CORE::GLOBAL::uc(...)> [perl #113016].
2799
2800=item *
2801
2802Calling an undefined sub whose typeglob has been undefined now produces the
2803customary "Undefined subroutine called" error, instead of "Not a CODE
2804reference".
2805
2806=item *
2807
2808Two bugs involving @ISA have been fixed. C<*ISA = *glob_without_array> and
2809C<undef *ISA; @{*ISA}> would prevent future modifications to @ISA from
2810updating the internal caches used to look up methods. The
e612b5a0 2811*glob_without_array case was a regression from Perl v5.12.
5ed58cbd
RS
2812
2813=item *
2814
2815Regular expression optimisations sometimes caused C<$> with C</m> to
2816produce failed or incorrect matches [perl #114068].
2817
2818=item *
2819
2820C<__SUB__> now works in a C<sort> block when the enclosing subroutine is
2821predeclared with C<sub foo;> syntax [perl #113710].
2822
2823=item *
2824
2825Unicode properties only apply to Unicode code points, which leads to
2826some subtleties when regular expressions are matched against
2827above-Unicode code points. There is a warning generated to draw your
2828attention to this. However, this warning was being generated
2829inappropriately in some cases, such as when a program was being parsed.
2830Non-Unicode matches such as C<\w> and C<[:word;]> should not generate the
2831warning, as their definitions don't limit them to apply to only Unicode
2832code points. Now the message is only generated when matching against
2833C<\p{}> and C<\P{}>. There remains a bug, [perl #114148], for the very
2834few properties in Unicode that match just a single code point. The
2835warning is not generated if they are matched against an above-Unicode
2836code point.
2837
2838=item *
2839
2840Uninitialized warnings mentioning hash elements would only mention the
2841element name if it was not in the first bucket of the hash, due to an
2842off-by-one error.
2843
2844=item *
2845
2846A regular expression optimizer bug could cause multiline "^" to behave
2847incorrectly in the presence of line breaks, such that
2848C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].
2849
2850=item *
2851
2852Failed C<fork> in list context no longer corrupts the stack.
2853C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
2854if the C<fork> call failed.
2855
2856=item *
2857
2858Numerous memory leaks have been fixed, mostly involving tied variables that
2859die, regular expression character classes and code blocks, and syntax
2860errors.
2861
2862=item *
2863
2864Assigning a regular expression (C<${qr//}>) to a variable that happens to
2865hold a floating point number no longer causes assertion failures on
2866debugging builds.
2867
2868=item *
2869
2870Assigning a regular expression to a scalar containing a number no longer
f105b7be 2871causes subsequent numification to produce random numbers.
5ed58cbd
RS
2872
2873=item *
2874
2875Assigning a regular expression to a magic variable no longer wipes away the
e612b5a0 2876magic. This was a regression from v5.10.
5ed58cbd
RS
2877
2878=item *
2879
2880Assigning a regular expression to a blessed scalar no longer results in
e612b5a0 2881crashes. This was also a regression from v5.10.
5ed58cbd
RS
2882
2883=item *
2884
2885Regular expression can now be assigned to tied hash and array elements with
2886flattening into strings.
2887
2888=item *
2889
f105b7be 2890Numifying a regular expression no longer results in an uninitialized
5ed58cbd
RS
2891warning.
2892
2893=item *
2894
2895Negative array indices no longer cause EXISTS methods of tied variables to
e612b5a0 2896be ignored. This was a regression from v5.12.
5ed58cbd
RS
2897
2898=item *
2899
2900Negative array indices no longer result in crashes on arrays tied to
2901non-objects.
2902
2903=item *
2904
be12dd22
RS
2905C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF-8 if the
2906left-hand scalar happened to have produced a UTF-8 string the last time
5ed58cbd
RS
2907overloading was invoked.
2908
2909=item *
2910
2911C<goto &sub> now uses the current value of @_, instead of using the array
2912the subroutine was originally called with. This means
2913C<local @_ = (...); goto &sub> now works [perl #43077].
2914
2915=item *
2916
2917If a debugger is invoked recursively, it no longer stomps on its own
2918lexical variables. Formerly under recursion all calls would share the same
2919set of lexical variables [perl #115742].
2920
2921=item *
2922
2923C<*_{ARRAY}> returned from a subroutine no longer spontaneously
2924becomes empty.
2925
2926=back
2927
2928=head1 Known Problems
2929
2930=over 4
2931
2932=item *
2933
7f50b25b 2934There are no known regressions. Please report any bugs you find!
5ed58cbd
RS
2935
2936=back
2937
2938=head1 Acknowledgements
a75569c0 2939
dd38235c
RS
2940Perl v5.18.0 represents approximately 12 months of development since
2941Perl v5.16.0 and contains approximately 400,000 lines of changes across
29422,100 files from 113 authors.
2943
2944Perl continues to flourish into its third decade thanks to a vibrant
2945community of users and developers. The following people are known to
2946have contributed the improvements that became Perl v5.18.0:
2947
2948Aaron Crane, Aaron Trevena, Abhijit Menon-Sen, Adrian M. Enache, Alan
2949Haggai Alavi, Alexandr Ciornii, Andrew Tam, Andy Dougherty, Anton Nikishaev,
2950Aristotle Pagaltzis, Augustina Blair, Bob Ernst, Brad Gilbert, Breno G. de
2951Oliveira, Brian Carlson, Brian Fraser, Charlie Gonzalez, Chip Salzenberg, Chris
2952'BinGOs' Williams, Christian Hansen, Colin Kuskie, Craig A. Berry, Dagfinn
2953Ilmari Mannsåker, Daniel Dragan, Daniel Perrett, Darin McBride, Dave Rolsky,
2954David Golden, David Leadbeater, David Mitchell, David Nicol, Dominic
2955Hargreaves, E. Choroba, Eric Brine, Evan Miller, Father Chrysostomos, Florian
2956Ragwitz, François Perrad, George Greer, Goro Fuji, H.Merijn Brand, Herbert
2957Breunung, Hugo van der Sanden, Igor Zaytsev, James E Keenan, Jan Dubois,
2958Jasmine Ahuja, Jerry D. Hedden, Jess Robinson, Jesse Luehrs, Joaquin Ferrero,
2959Joel Berger, John Goodyear, John Peacock, Karen Etheridge, Karl Williamson,
2960Karthik Rajagopalan, Kent Fredric, Leon Timmermans, Lucas Holt, Lukas Mai,
2961Marcus Holland-Moritz, Markus Jansen, Martin Hasch, Matthew Horsfall, Max
2962Maischein, Michael G Schwern, Michael Schroeder, Moritz Lenz, Nicholas Clark,
2963Niko Tyni, Oleg Nesterov, Patrik Hägglund, Paul Green, Paul Johnson, Paul
2964Marquess, Peter Martini, Rafael Garcia-Suarez, Reini Urban, Renee Baecker,
2965Rhesa Rozendaal, Ricardo Signes, Robin Barker, Ronald J. Kimball, Ruslan
2966Zakirov, Salvador Fandiño, Sawyer X, Scott Lanning, Sergey Alekseev, Shawn M
2967Moore, Shirakata Kentaro, Shlomi Fish, Sisyphus, Smylers, Steffen Müller,
2968Steve Hay, Steve Peters, Steven Schubiger, Sullivan Beck, Sven Strickroth,
2969Sébastien Aperghis-Tramoni, Thomas Sibley, Tobias Leich, Tom Wyant, Tony Cook,
2970Vadim Konovalov, Vincent Pit, Volker Schatz, Walt Mankowski, Yves Orton,
2971Zefram.
2972
2973The list above is almost certainly incomplete as it is automatically generated
2974from version control history. In particular, it does not include the names of
2975the (very much appreciated) contributors who reported issues to the Perl bug
2976tracker.
2977
2978Many of the changes included in this version originated in the CPAN modules
2979included in Perl's core. We're grateful to the entire CPAN community for
2980helping Perl to flourish.
2981
2982For a more complete list of all of Perl's historical contributors, please see
2983the F<AUTHORS> file in the Perl source distribution.
f5b73711 2984
44691e6f
AB
2985=head1 Reporting Bugs
2986
e08634c5
SH
2987If you find what you think is a bug, you might check the articles recently
2988posted to the comp.lang.perl.misc newsgroup and the perl bug database at
2989http://rt.perl.org/perlbug/ . There may also be information at
2990http://www.perl.org/ , the Perl Home Page.
44691e6f 2991
e08634c5
SH
2992If you believe you have an unreported bug, please run the L<perlbug> program
2993included with your release. Be sure to trim your bug down to a tiny but
2994sufficient test case. Your bug report, along with the output of C<perl -V>,
2995will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
44691e6f
AB
2996
2997If the bug you are reporting has security implications, which make it
e08634c5
SH
2998inappropriate to send to a publicly archived mailing list, then please send it
2999to perl5-security-report@perl.org. This points to a closed subscription
3000unarchived mailing list, which includes all the core committers, who will be
3001able to help assess the impact of issues, figure out a resolution, and help
f9001595 3002co-ordinate the release of patches to mitigate or fix the problem across all
e08634c5
SH
3003platforms on which Perl is supported. Please only use this address for
3004security issues in the Perl core, not for modules independently distributed on
3005CPAN.
44691e6f
AB
3006
3007=head1 SEE ALSO
3008
e08634c5
SH
3009The F<Changes> file for an explanation of how to view exhaustive details on
3010what changed.
44691e6f
AB
3011
3012The F<INSTALL> file for how to build Perl.
3013
3014The F<README> file for general stuff.
3015
3016The F<Artistic> and F<Copying> files for copyright information.
3017
3018=cut