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Fix regex /il and /iaa failures for single element [] class
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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:
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KE
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
KE
614
615 U+2029 PARAGRAPH SEPARATOR.
5ed58cbd
RS
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
RS
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
RS
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
RS
700=head1 Future Deprecations
701
702=over
71e6aba6
RS
703
704=item *
705
4263dd11 706Platforms without support infrastructure
5ed58cbd
RS
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
RS
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
847This is only an overview of selected module updates. For a complete
848list of updates, run:
849
f105b7be 850 $ corelist --diff 5.16.0 5.18.0
5ed58cbd 851
e612b5a0 852You can substitute your favorite version in place of C<5.16.0>, too.
5ed58cbd
RS
853
854=over 4
33392251
BF
855
856=item *
857
5ed58cbd
RS
858L<XXX> has been upgraded from version A.xx to B.yy.
859
860=back
861
862=head2 Removed Modules and Pragmata
863
864=over
33392251
BF
865
866=item *
867
5ed58cbd
RS
868L<Version::Requirements> has been removed from the core distribution. It is
869available under a different name: L<CPAN::Meta::Requirements>.
2426c394 870
337fb649 871=back
2426c394 872
5ed58cbd 873=head1 Documentation
19718730 874
5ed58cbd
RS
875=head2 Changes to Existing Documentation
876
877=head3 L<perlcheat>
82d98f72 878
5a6a30f4 879=over 4
b7c7d786 880
5ed58cbd
RS
881=item *
882
883L<perlcheat> has been reorganized, and a few new sections were added.
884
885=back
886
887=head3 L<perldata>
888
889=over 4
82d98f72 890
5ed58cbd 891=item *
d2d1e842 892
5ed58cbd
RS
893Now explicitly documents the behaviour of hash initializer lists that
894contain duplicate keys.
f355e93d 895
5a6a30f4 896=back
f355e93d 897
5ed58cbd 898=head3 L<perldiag>
19718730 899
19718730 900=over 4
e14ac59b 901
5ed58cbd
RS
902=item *
903
904The explanation of symbolic references being prevented by "strict refs"
905now doesn't assume that the reader knows what symbolic references are.
906
907=back
9f351b45 908
5ed58cbd 909=head3 L<perlfaq>
9f351b45 910
5ed58cbd 911=over 4
9f351b45 912
5ed58cbd 913=item *
7cf3104f 914
5ed58cbd 915L<perlfaq> has been synchronized with version 5.0150040 from CPAN.
12719193 916
6253ee75 917=back
216cf7fc 918
5ed58cbd 919=head3 L<perlfunc>
f5b73711 920
5ed58cbd
RS
921=over 4
922
923=item *
a75569c0 924
5ed58cbd 925The return value of C<pipe> is now documented.
a75569c0 926
5ed58cbd 927=item *
a75569c0 928
5ed58cbd
RS
929Clarified documentation of C<our>.
930
931=back
932
933=head3 L<perlop>
934
935=over 4
936
937=item *
938
939Loop control verbs (C<dump>, C<goto>, C<next>, C<last> and C<redo>) have always
940had the same precedence as assignment operators, but this was not documented
941until now.
942
943=back
944
945=head3 Diagnostics
946
947The following additions or changes have been made to diagnostic output,
948including warnings and fatal error messages. For the complete list of
949diagnostic messages, see L<perldiag>.
950
5ed58cbd
RS
951=head2 New Diagnostics
952
5ed58cbd
RS
953=head3 New Errors
954
955=over 4
956
957=item *
958
959L<Unterminated delimiter for here document|perldiag/"Unterminated delimiter for here document">
960
961This message now occurs when a here document label has an initial quotation
962mark but the final quotation mark is missing.
963
964This replaces a bogus and misleading error message about not finding the label
965itself [perl #114104].
966
967=item *
968
969L<panic: child pseudo-process was never scheduled|perldiag/"panic: child pseudo-process was never scheduled">
970
971This error is thrown when a child pseudo-process in the ithreads implementation
972on Windows was not scheduled within the time period allowed and therefore was
973not able to initialize properly [perl #88840].
974
975=item *
976
977L<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/">
978
979This error has been added for C<(?&0)>, which is invalid. It used to
980produce an incomprehensible error message [perl #101666].
981
982=item *
983
984L<Can't use an undefined value as a subroutine reference|perldiag/"Can't use an undefined value as %s reference">
985
986Calling an undefined value as a subroutine now produces this error message.
987It used to, but was accidentally disabled, first in Perl 5.004 for
e612b5a0 988non-magical variables, and then in Perl v5.14 for magical (e.g., tied)
5ed58cbd
RS
989variables. It has now been restored. In the mean time, undef was treated
990as an empty string [perl #113576].
991
992=item *
993
994L<Experimental "%s" subs not enabled|perldiag/"Experimental "%s" subs not enabled">
995
996To use lexical subs, you must first enable them:
997
998 no warnings 'experimental::lexical_subs';
999 use feature 'lexical_subs';
1000 my sub foo { ... }
1001
1002=back
1003
1004=head3 New Warnings
1005
1006=over 4
1007
1008=item *
1009
1010XXX: This needs more detail.
1011
1012Strings with code points over 0xFF may not be mapped into in-memory file
1013handles
1014
1015=item *
1016
1017L<'%s' resolved to '\o{%s}%d'|perldiag/"'%s' resolved to '\o{%s}%d'">
1018
1019=item *
1020
1021L<'Trailing white-space in a charnames alias definition is deprecated'|perldiag/"Trailing white-space in a charnames alias definition is deprecated">
1022
1023=item *
1024
1025L<'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">
1026
1027=item *
1028
1029L<'Passing malformed UTF-8 to "%s" is deprecated'|perldiag/"Passing malformed UTF-8 to "%s" is deprecated">
1030
1031=item *
1032
1033L<Subroutine "&%s" is not available|perldiag/"Subroutine "&%s" is not available">
1034
1035(W closure) During compilation, an inner named subroutine or eval is
1036attempting to capture an outer lexical subroutine that is not currently
1037available. This can happen for one of two reasons. First, the lexical
1038subroutine may be declared in an outer anonymous subroutine that has not
1039yet been created. (Remember that named subs are created at compile time,
1040while anonymous subs are created at run-time.) For example,
1041
1042 sub { my sub a {...} sub f { \&a } }
1043
1044At the time that f is created, it can't capture the current the "a" sub,
1045since the anonymous subroutine hasn't been created yet. Conversely, the
1046following won't give a warning since the anonymous subroutine has by now
1047been created and is live:
1048
1049 sub { my sub a {...} eval 'sub f { \&a }' }->();
1050
1051The second situation is caused by an eval accessing a variable that has
1052gone out of scope, for example,
1053
1054 sub f {
1055 my sub a {...}
1056 sub { eval '\&a' }
1057 }
1058 f()->();
1059
1060Here, when the '\&a' in the eval is being compiled, f() is not currently
1061being executed, so its &a is not available for capture.
1062
1063=item *
1064
1065L<"%s" subroutine &%s masks earlier declaration in same %s|perldiag/"%s" subroutine &%s masks earlier declaration in same %s>
1066
1067(W misc) A "my" or "state" subroutine has been redeclared in the
1068current scope or statement, effectively eliminating all access to
1069the previous instance. This is almost always a typographical error.
1070Note that the earlier subroutine will still exist until the end of
1071the scope or until all closure references to it are destroyed.
1072
1073=item *
1074
1075L<The %s feature is experimental|perldiag/"The %s feature is experimental">
1076
1077(S experimental) This warning is emitted if you enable an experimental
1078feature via C<use feature>. Simply suppress the warning if you want
1079to use the feature, but know that in doing so you are taking the risk
1080of using an experimental feature which may change or be removed in a
1081future Perl version:
1082
1083 no warnings "experimental::lexical_subs";
1084 use feature "lexical_subs";
1085
1086=item *
1087
1088L<sleep(%u) too large|perldiag/"sleep(%u) too large">
1089
1090(W overflow) You called C<sleep> with a number that was larger than it can
1091reliably handle and C<sleep> probably slept for less time than requested.
1092
1093=item *
1094
1095L<Wide character in setenv|perldiag/"Wide character in %s">
1096
1097Attempts to put wide characters into environment variables via C<%ENV> now
1098provoke this warning.
1099
1100=item *
1101
1102"L<Invalid negative number (%s) in chr|perldiag/"Invalid negative number (%s) in chr">"
1103
1104C<chr()> now warns when passed a negative value [perl #83048].
1105
1106=item *
1107
1108"L<Integer overflow in srand|perldiag/"Integer overflow in srand">"
1109
1110C<srand()> now warns when passed a value that doesn't fit in a C<UV> (since the
1111value will be truncated rather than overflowing) [perl #40605].
1112
1113=item *
1114
1115"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">"
1116
1117Running perl with the C<-i> flag now warns if no input files are provided on
1118the command line [perl #113410].
1119
1120=back
1121
1122=head2 Changes to Existing Diagnostics
1123
1124=over 4
1125
1126=item *
1127
1128L<$* is no longer supported|perldiag/"$* is no longer supported">
1129
1130The warning that use of C<$*> and C<$#> is no longer supported is now
1131generated for every location that references them. Previously it would fail
1132to be generated if another variable using the same typeglob was seen first
1133(e.g. C<@*> before C<$*>), and would not be generated for the second and
1134subsequent uses. (It's hard to fix the failure to generate warnings at all
1135without also generating them every time, and warning every time is
1136consistent with the warnings that C<$[> used to generate.)
1137
1138=item *
1139
1140The warnings for C<\b{> and C<\B{> were added. They are a deprecation
1141warning which should be turned off by that category. One should not
1142have to turn off regular regexp warnings as well to get rid of these.
1143
1144=item *
1145
1146L<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>
1147
1148Constant overloading that returns C<undef> results in this error message.
1149For numeric constants, it used to say "Constant(undef)". "undef" has been
1150replaced with the number itself.
1151
1152=item *
1153
1154The error produced when a module cannot be loaded now includes a hint that
1155the module may need to be installed: "Can't locate hopping.pm in @INC (you
1156may need to install the hopping module) (@INC contains: ...)"
1157
1158=item *
1159
1160L<vector argument not supported with alpha versions|perldiag/vector argument not supported with alpha versions>
1161
1162This warning was not suppressable, even with C<no warnings>. Now it is
1163suppressible, and has been moved from the "internal" category to the
1164"printf" category.
1165
1166=item *
1167
1168C<< Can't do {n,m} with n > m in regex; marked by <-- HERE in m/%s/ >>
1169
1170This fatal error has been turned into a warning that reads:
1171
1172L<< Quantifier {n,m} with n > m can't match in regex | perldiag/Quantifier {n,m} with n > m can't match in regex >>
1173
1174(W regexp) Minima should be less than or equal to maxima. If you really want
1175your regexp to match something 0 times, just put {0}.
1176
1177=item *
1178
1179The "Runaway prototype" warning that occurs in bizarre cases has been
1180removed as being unhelpful and inconsistent.
1181
1182=item *
1183
1184The "Not a format reference" error has been removed, as the only case in
1185which it could be triggered was a bug.
1186
1187=item *
1188
1189The "Unable to create sub named %s" error has been removed for the same
1190reason.
1191
1192=item *
1193
1194The 'Can't use "my %s" in sort comparison' error has been downgraded to a
1195warning, '"my %s" used in sort comparison' (with 'state' instead of 'my'
1196for state variables). In addition, the heuristics for guessing whether
1197lexical $a or $b has been misused have been improved to generate fewer
1198false positives. Lexical $a and $b are no longer disallowed if they are
1199outside the sort block. Also, a named unary or list operator inside the
1200sort block no longer causes the $a or $b to be ignored [perl #86136].
1201
1202=back
1203
1204=head1 Utility Changes
1205
1206=head3 L<h2xs>
1207
1208=over 4
1209
1210=item *
1211
1212F<h2xs> no longer produces invalid code for empty defines. [perl #20636]
1213
1214=back
1215
1216=head1 Configuration and Compilation
1217
1218=over 4
1219
1220=item *
1221
1222Added C<useversionedarchname> option to Configure
1223
1224When set, it includes 'api_versionstring' in 'archname'. E.g.
1225x86_64-linux-5.13.6-thread-multi. It is unset by default.
1226
1227This feature was requested by Tim Bunce, who observed that
f105b7be 1228C<INSTALL_BASE> creates a library structure that does not
5ed58cbd
RS
1229differentiate by perl version. Instead, it places architecture
1230specific files in "$install_base/lib/perl5/$archname". This makes
f105b7be 1231it difficult to use a common C<INSTALL_BASE> library path with
5ed58cbd
RS
1232multiple versions of perl.
1233
f105b7be 1234By setting C<-Duseversionedarchname>, the $archname will be
c2959982 1235distinct for architecture I<and> API version, allowing mixed use of
f105b7be 1236C<INSTALL_BASE>.
5ed58cbd
RS
1237
1238=item *
1239
ff772877
RS
1240Add a C<PERL_NO_INLINE_FUNCTIONS> option
1241
f105b7be 1242If C<PERL_NO_INLINE_FUNCTIONS> is defined, don't include "inline.h"
ff772877
RS
1243
1244This permits test code to include the perl headers for definitions without
1245creating a link dependency on the perl library (which may not exist yet).
1246
1247=item *
1248
5ed58cbd
RS
1249Configure will honour the external C<MAILDOMAIN> environment variable, if set.
1250
1251=item *
1252
1253C<installman> no longer ignores the silent option
1254
1255=item *
1256
1257Both C<META.yml> and C<META.json> files are now included in the distribution.
1258
1259=item *
1260
1261F<Configure> will now correctly detect C<isblank()> when compiling with a C++
1262compiler.
1263
1264=item *
1265
1266The pager detection in F<Configure> has been improved to allow responses which
1267specify options after the program name, e.g. B</usr/bin/less -R>, if the user
1268accepts the default value. This helps B<perldoc> when handling ANSI escapes
1269[perl #72156].
1270
1271=back
1272
1273=head1 Testing
1274
1275=over 4
1276
1277=item *
1278
1279The test suite now has a section for tests that require very large amounts
1280of memory. These tests won't run by default; they can be enabled by
1281setting the C<PERL_TEST_MEMORY> environment variable to the number of
1282gibibytes of memory that may be safely used.
1283
1284=back
1285
1286=head1 Platform Support
1287
1288=head2 Discontinued Platforms
1289
1290=over 4
1291
1292=item BeOS
1293
1294BeOS was an operating system for personal computers developed by Be Inc,
1295initially for their BeBox hardware. The OS Haiku was written as an open
1296source replacement for/continuation of BeOS, and its perl port is current and
1297actively maintained.
1298
1299=item UTS Global
1300
1301Support code relating to UTS global has been removed. UTS was a mainframe
1302version of System V created by Amdahl, subsequently sold to UTS Global. The
e612b5a0 1303port has not been touched since before Perl v5.8.0, and UTS Global is now
5ed58cbd
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1304defunct.
1305
1306=item VM/ESA
1307
1308Support for VM/ESA has been removed. The port was tested on 2.3.0, which
1309IBM ended service on in March 2002. 2.4.0 ended service in June 2003, and
1310was superseded by Z/VM. The current version of Z/VM is V6.2.0, and scheduled
1311for end of service on 2015/04/30.
1312
1313=item MPE/IX
1314
1315Support for MPE/IX has been removed.
1316
1317=item EPOC
1318
1319Support code relating to EPOC has been removed. EPOC was a family of
1320operating systems developed by Psion for mobile devices. It was the
1321predecessor of Symbian. The port was last updated in April 2002.
1322
1323=item Rhapsody
1324
1325Support for Rhapsody has been removed.
1326
1327=back
1328
1329=head2 Platform-Specific Notes
1330
1331=head3 AIX
1332
1333Configure now always adds C<-qlanglvl=extc99> to the CC flags on AIX when
1334using xlC. This will make it easier to compile a number of XS-based modules
1335that assume C99 [perl #113778].
1336
1337=head3 clang++
1338
1339There is now a workaround for a compiler bug that prevented compiling
e612b5a0 1340with clang++ since Perl v5.15.7 [perl #112786].
5ed58cbd
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1341
1342=head3 C++
1343
1344When compiling the Perl core as C++ (which is only semi-supported), the
1345mathom functions are now compiled as C<extern "C">, to ensure proper
1346binary compatibility. (However, binary compatibility isn't generally
1347guaranteed anyway in the situations where this would matter.)
1348
1349=head3 Darwin
1350
1351Stop hardcoding an alignment on 8 byte boundaries to fix builds using
1352-Dusemorebits.
1353
1354=head3 Haiku
1355
1356Perl should now work out of the box on Haiku R1 Alpha 4.
1357
1358=head3 MidnightBSD
1359
1360C<libc_r> was removed from recent versions of MidnightBSD and older versions
1361work better with C<pthread>. Threading is now enabled using C<pthread> which
1362corrects build errors with threading enabled on 0.4-CURRENT.
1363
1364=head3 Solaris
1365
1366In Configure, avoid running sed commands with flags not supported on Solaris.
1367
1368=head3 VMS
1369
1370=over
1371
1372=item *
1373
1374Where possible, the case of filenames and command-line arguments is now
1375preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
1376C<DECC$ARGV_PARSE_STYLE> at start-up time. The latter only takes effect
1377when extended parse is enabled in the process from which Perl is run.
1378
1379=item *
1380
1381The character set for Extended Filename Syntax (EFS) is now enabled by default
1382on VMS. Among other things, this provides better handling of dots in directory
05f5908f 1383names, multiple dots in filenames, and spaces in filenames. To obtain the old
5ed58cbd
RS
1384behavior, set the logical name C<DECC$EFS_CHARSET> to C<DISABLE>.
1385
1386=item *
1387
05f5908f 1388Fixed linking on builds configured with C<-Dusemymalloc=y>.
5ed58cbd
RS
1389
1390=item *
1391
05f5908f
CB
1392Experimental support for building Perl with the HP C++ compiler is available
1393by configuring with C<-Dusecxx>.
5ed58cbd
RS
1394
1395=item *
1396
1397All C header files from the top-level directory of the distribution are now
1398installed on VMS, providing consistency with a long-standing practice on other
1399platforms. Previously only a subset were installed, which broke non-core
1400extension builds for extensions that depended on the missing include files.
1401
1402=item *
1403
1404Quotes are now removed from the command verb (but not the parameters) for
1405commands spawned via C<system>, backticks, or a piped C<open>. Previously,
1406quotes on the verb were passed through to DCL, which would fail to recognize
1407the command. Also, if the verb is actually a path to an image or command
1408procedure on an ODS-5 volume, quoting it now allows the path to contain spaces.
1409
1410=item *
1411
1412The B<a2p> build has been fixed for the HP C++ compiler on OpenVMS.
1413
1414=back
1415
1416=head3 Win32
1417
1418=over
1419
1420=item *
1421
1422Perl can now be built using Microsoft's Visual C++ 2012 compiler by specifying
1423CCTYPE=MSVC110 (or MSVC110FREE if you are using the free Express edition for
1424Windows Desktop) in F<win32/Makefile>.
1425
1426=item *
1427
f105b7be 1428The option to build without C<USE_SOCKETS_AS_HANDLES> has been removed.
5ed58cbd
RS
1429
1430=item *
1431
1432Fixed a problem where perl could crash while cleaning up threads (including the
1433main thread) in threaded debugging builds on Win32 and possibly other platforms
1434[perl #114496].
1435
1436=item *
1437
1438A rare race condition that would lead to L<sleep|perlfunc/sleep> taking more
1439time than requested, and possibly even hanging, has been fixed [perl #33096].
1440
1441=item *
1442
1443C<link> on Win32 now attempts to set C<$!> to more appropriate values
1444based on the Win32 API error code. [perl #112272]
1445
1446Perl no longer mangles the environment block, e.g. when launching a new
1447sub-process, when the environment contains non-ASCII characters. Known
1448problems still remain, however, when the environment contains characters
1449outside of the current ANSI codepage (e.g. see the item about Unicode in
1450C<%ENV> in L<http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod>).
1451[perl #113536]
1452
1453=item *
1454
1455Building perl with some Windows compilers used to fail due to a problem
1456with miniperl's C<glob> operator (which uses the C<perlglob> program)
1457deleting the PATH environment variable [perl #113798].
1458
1459=item *
1460
f105b7be 1461A new makefile option, C<USE_64_BIT_INT>, has been added to the Windows
5ed58cbd
RS
1462makefiles. Set this to "define" when building a 32-bit perl if you want
1463it to use 64-bit integers.
1464
1465Machine code size reductions, already made to the DLLs of XS modules in
e612b5a0 1466Perl v5.17.2, have now been extended to the perl DLL itself.
5ed58cbd 1467
e612b5a0 1468Building with VC++ 6.0 was inadvertently broken in Perl v5.17.2 but has
5ed58cbd
RS
1469now been fixed again.
1470
1471=back
1472
1473=head3 WinCE
1474
1475Building on WinCE is now possible once again, although more work is required
1476to fully restore a clean build.
1477
1478=head1 Internal Changes
1479
1480=over
1481
1482=item *
1483
4263dd11 1484Synonyms for the misleadingly named C<av_len()> have been created:
5ed58cbd
RS
1485C<av_top_index()> and C<av_tindex>. All three of these return the
1486number of the highest index in the array, not the number of elements it
1487contains.
1488
1489=item *
1490
1491SvUPGRADE() is no longer an expression. Originally this macro (and its
1492underlying function, sv_upgrade()) were documented as boolean, although
1493in reality they always croaked on error and never returned false. In 2005
1494the documentation was updated to specify a void return value, but
1495SvUPGRADE() was left always returning 1 for backwards compatibility. This
1496has now been removed, and SvUPGRADE() is now a statement with no return
1497value.
1498
1499So this is now a syntax error:
1500
1501 if (!SvUPGRADE(sv)) { croak(...); }
1502
1503If you have code like that, simply replace it with
1504
1505 SvUPGRADE(sv);
1506
1507or to to avoid compiler warnings with older perls, possibly
1508
1509 (void)SvUPGRADE(sv);
1510
1511=item *
1512
1513Perl has a new copy-on-write mechanism that allows any SvPOK scalar to be
1514upgraded to a copy-on-write scalar. A reference count on the string buffer
d16360cf
RS
1515is stored in the string buffer itself. This feature is B<not enabled by
1516default>.
5ed58cbd 1517
d16360cf
RS
1518It can be enabled in a perl build by running F<Configure> with
1519B<-Accflags=-DPERL_NEW_COPY_ON_WRITE>, and we would encourage XS authors
1520to try their code with such an enabled perl, and provide feedback.
1521Unfortunately, there is not yet a good guide to updating XS code to cope
1522with COW. Until such a document is available, consult the perl5-porters
1523mailing list.
5ed58cbd 1524
d16360cf
RS
1525It breaks a few XS modules by allowing copy-on-write scalars to go
1526through code paths that never encountered them before.
5ed58cbd
RS
1527
1528=item *
1529
1530Copy-on-write no longer uses the SvFAKE and SvREADONLY flags. Hence,
1531SvREADONLY indicates a true read-only SV.
1532
1533Use the SvIsCOW macro (as before) to identify a copy-on-write scalar.
1534
1535=item *
1536
f105b7be 1537C<PL_glob_index> is gone.
5ed58cbd
RS
1538
1539=item *
1540
1541The private Perl_croak_no_modify has had its context parameter removed. It is
1542now has a void prototype. Users of the public API croak_no_modify remain
1543unaffected.
1544
1545=item *
1546
1547Copy-on-write (shared hash key) scalars are no longer marked read-only.
1548C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
1549true.
1550
1551=item *
1552
1553A new op type, C<OP_PADRANGE> has been introduced. The perl peephole
1554optimiser will, where possible, substitute a single padrange op for a
1555pushmark followed by one or more pad ops, and possibly also skipping list
1556and nextstate ops. In addition, the op can carry out the tasks associated
f105b7be 1557with the RHS of a C<< my(...) = @_ >> assignment, so those ops may be optimised
5ed58cbd
RS
1558away too.
1559
1560=item *
1561
1562Case-insensitive matching inside a [bracketed] character class with a
1563multi-character fold no longer excludes one of the possibilities in the
1564circumstances that it used to. [perl #89774].
1565
1566=item *
1567
1568C<PL_formfeed> has been removed.
1569
1570=item *
1571
1572The regular expression engine no longer reads one byte past the end of the
1573target string. While for all internally well-formed scalars this should
1574never have been a problem, this change facilitates clever tricks with
1575string buffers in CPAN modules. [perl #73542]
1576
1577=item *
1578
1579Inside a BEGIN block, C<PL_compcv> now points to the currently-compiling
1580subroutine, rather than the BEGIN block itself.
1581
1582=item *
1583
1584C<mg_length> has been deprecated.
1585
1586=item *
1587
1588C<sv_len> now always returns a byte count and C<sv_len_utf8> a character
1589count. Previously, C<sv_len> and C<sv_len_utf8> were both buggy and would
1590sometimes returns bytes and sometimes characters. C<sv_len_utf8> no longer
be12dd22 1591assumes that its argument is in UTF-8. Neither of these creates UTF-8 caches
5ed58cbd
RS
1592for tied or overloaded values or for non-PVs any more.
1593
1594=item *
1595
1596C<sv_mortalcopy> now copies string buffers of shared hash key scalars when
1597called from XS modules [perl #79824].
1598
1599=item *
1600
1601C<RXf_SPLIT> and C<RXf_SKIPWHITE> are no longer used. They are now
1602#defined as 0.
1603
1604=item *
1605
1606The new C<RXf_MODIFIES_VARS> flag can be set by custom regular expression
1607engines to indicate that the execution of the regular expression may cause
1608variables to be modified. This lets C<s///> know to skip certain
1609optimisations. Perl's own regular expression engine sets this flag for the
1610special backtracking verbs that set $REGMARK and $REGERROR.
1611
1612=item *
1613
1614The APIs for accessing lexical pads have changed considerably.
1615
1616C<PADLIST>s are now longer C<AV>s, but their own type instead.
1617C<PADLIST>s now contain a C<PAD> and a C<PADNAMELIST> of C<PADNAME>s,
1618rather than C<AV>s for the pad and the list of pad names. C<PAD>s,
1619C<PADNAMELIST>s, and C<PADNAME>s are to be accessed as such through the
1620newly added pad API instead of the plain C<AV> and C<SV> APIs. See
1621L<perlapi> for details.
1622
1623=item *
1624
1625In the regex API, the numbered capture callbacks are passed an index
1626indicating what match variable is being accessed. There are special
1627index values for the C<$`, $&, $&> variables. Previously the same three
1628values were used to retrieve C<${^PREMATCH}, ${^MATCH}, ${^POSTMATCH}>
1629too, but these have now been assigned three separate values. See
1630L<perlreapi/Numbered capture callbacks>.
1631
1632=item *
1633
1634C<PL_sawampersand> was previously a boolean indicating that any of
1635C<$`, $&, $&> had been seen; it now contains three one-bit flags
1636indicating the presence of each of the variables individually.
1637
1638=item *
1639
1640The C<CV *> typemap entry now supports C<&{}> overloading and typeglobs,
1641just like C<&{...}> [perl #96872].
1642
1643=item *
1644
1645The C<SVf_AMAGIC> flag to indicate overloading is now on the stash, not the
1646object. It is now set automatically whenever a method or @ISA changes, so
1647its meaning has changed, too. It now means "potentially overloaded". When
1648the overload table is calculated, the flag is automatically turned off if
1649there is no overloading, so there should be no noticeable slowdown.
1650
1651The staleness of the overload tables is now checked when overload methods
1652are invoked, rather than during C<bless>.
1653
1654"A" magic is gone. The changes to the handling of the C<SVf_AMAGIC> flag
1655eliminate the need for it.
1656
1657C<PL_amagic_generation> has been removed as no longer necessary. For XS
1658modules, it is now a macro alias to C<PL_na>.
1659
1660The fallback overload setting is now stored in a stash entry separate from
1661overloadedness itself.
1662
1663=item *
1664
1665The character-processing code has been cleaned up in places. The changes
1666should be operationally invisible.
1667
1668=item *
1669
e612b5a0 1670The C<study> function was made a no-op in v5.16. It was simply disabled via
5ed58cbd
RS
1671a C<return> statement; the code was left in place. Now the code supporting
1672what C<study> used to do has been removed.
1673
1674=item *
1675
1676Under threaded perls, there is no longer a separate PV allocated for every
1677COP to store its package name (C<< cop->stashpv >>). Instead, there is an
1678offset (C<< cop->stashoff >>) into the new C<PL_stashpad> array, which
1679holds stash pointers.
1680
1681=item *
1682
1683In the pluggable regex API, the C<regexp_engine> struct has acquired a new
1684field C<op_comp>, which is currently just for perl's internal use, and
f105b7be 1685should be initialized to NULL by other regex plugin modules.
5ed58cbd
RS
1686
1687=item *
1688
7779650e 1689A new function C<alloccopstash> has been added to the API, but is considered
5ed58cbd
RS
1690experimental. See L<perlapi>.
1691
1692=item *
1693
1694Perl used to implement get magic in a way that would sometimes hide bugs in
4263dd11 1695code that could call mg_get() too many times on magical values. This hiding of
5ed58cbd
RS
1696errors no longer occurs, so long-standing bugs may become visible now. If
1697you see magic-related errors in XS code, check to make sure it, together
1698with the Perl API functions it uses, calls mg_get() only once on SvGMAGICAL()
1699values.
1700
1701=item *
1702
1703OP allocation for CVs now uses a slab allocator. This simplifies
1704memory management for OPs allocated to a CV, so cleaning up after a
1705compilation error is simpler and safer [perl #111462][perl #112312].
1706
1707=item *
1708
f105b7be 1709C<PERL_DEBUG_READONLY_OPS> has been rewritten to work with the new slab
5ed58cbd
RS
1710allocator, allowing it to catch more violations than before.
1711
1712=item *
1713
f105b7be
KE
1714The old slab allocator for ops, which was only enabled for C<PERL_IMPLICIT_SYS>
1715and C<PERL_DEBUG_READONLY_OPS>, has been retired.
5ed58cbd
RS
1716
1717=back
1718
1719=head1 Selected Bug Fixes
1720
1721=over 4
1722
1723=item *
1724
1725Here-doc terminators no longer require a terminating newline character when
1726they occur at the end of a file. This was already the case at the end of a
1727string eval [perl #65838].
1728
1729=item *
1730
f105b7be 1731C<-DPERL_GLOBAL_STRUCT> builds now free the global struct B<after>
5ed58cbd
RS
1732they've finished using it.
1733
1734=item *
1735
1736A trailing '/' on a path in @INC will no longer have an additional '/'
1737appended.
1738
1739=item *
1740
1741The C<:crlf> layer now works when unread data doesn't fit into its own
1742buffer. [perl #112244].
1743
1744=item *
1745
1746C<ungetc()> now handles UTF-8 encoded data. [perl #116322].
1747
1748=item *
1749
1750A bug in the core typemap caused any C types that map to the T_BOOL core
1751typemap entry to not be set, updated, or modified when the T_BOOL variable was
1752used in an OUTPUT: section with an exception for RETVAL. T_BOOL in an INPUT:
1753section was not affected. Using a T_BOOL return type for an XSUB (RETVAL)
1754was not affected. A side effect of fixing this bug is, if a T_BOOL is specified
1755in the OUTPUT: section (which previous did nothing to the SV), and a read only
1756SV (literal) is passed to the XSUB, croaks like "Modification of a read-only
1757value attempted" will happen. [perl #115796]
1758
1759=item *
1760
1761On many platforms, providing a directory name as the script name caused perl
1762to do nothing and report success. It should now universally report an error
1763and exit nonzero. [perl #61362]
1764
1765=item *
1766
1767C<sort {undef} ...> under fatal warnings no longer crashes. It had
e612b5a0 1768begun crashing in Perl v5.16.
5ed58cbd
RS
1769
1770=item *
1771
1772Stashes blessed into each other
1773(C<bless \%Foo::, 'Bar'; bless \%Bar::, 'Foo'>) no longer result in double
e612b5a0 1774frees. This bug started happening in Perl v5.16.
5ed58cbd
RS
1775
1776=item *
1777
1778Numerous memory leaks have been fixed, mostly involving fatal warnings and
1779syntax errors.
1780
1781=item *
1782
1783Some failed regular expression matches such as C<'f' =~ /../g> were not
1784resetting C<pos>. Also, "match-once" patterns (C<m?...?g>) failed to reset
1785it, too, when invoked a second time [perl #23180].
1786
1787=item *
1788
1789Accessing C<$&> after a pattern match now works if it had not been seen
1790before the match. I.e., this applies to C<${'&'}> (under C<no strict>) and
1791C<eval '$&'>. The same applies to C<$'> and C<$`> [perl #4289].
1792
1793=item *
1794
1795Several bugs involving C<local *ISA> and C<local *Foo::> causing stale
1796MRO caches have been fixed.
1797
1798=item *
1799
1800Defining a subroutine when its typeglob has been aliased no longer results
e612b5a0 1801in stale method caches. This bug was introduced in Perl v5.10.
5ed58cbd
RS
1802
1803=item *
1804
1805Localising a typeglob containing a subroutine when the typeglob's package
1806has been deleted from its parent stash no longer produces an error. This
e612b5a0 1807bug was introduced in Perl v5.14.
5ed58cbd
RS
1808
1809=item *
1810
1811Under some circumstances, C<local *method=...> would fail to reset method
1812caches upon scope exit.
1813
1814=item *
1815
1816C</[.foo.]/> is no longer an error, but produces a warning (as before) and
1817is treated as C</[.fo]/> [perl #115818].
1818
1819=item *
1820
1821C<goto $tied_var> now calls FETCH before deciding what type of goto
1822(subroutine or label) this is.
1823
1824=item *
1825
1826Renaming packages through glob assignment
1827(C<*Foo:: = *Bar::; *Bar:: = *Baz::>) in combination with C<m?...?> and
1828C<reset> no longer makes threaded builds crash.
1829
1830=item *
1831
1832A number of bugs related to assigning a list to hash have been fixed. Many of
1833these involve lists with repeated keys like C<(1, 1, 1, 1)>.
1834
1835=over 4
1836
1837=item *
1838
1839The expression C<scalar(%h = (1, 1, 1, 1))> now returns C<4>, not C<2>.
1840
1841=item *
1842
1843The return value of C<%h = (1, 1, 1)> in list context was wrong. Previously
1844this would return C<(1, undef, 1)>, now it returns C<(1, undef)>.
1845
1846=item *
1847
1848Perl now issues the same warning on C<($s, %h) = (1, {})> as it does for
1849C<(%h) = ({})>, "Reference found where even-sized list expected".
1850
1851=item *
1852
1853A number of additional edge cases in list assignment to hashes were
1854corrected. For more details see commit 23b7025ebc.
1855
1856=back
1857
1858=item *
1859
1860Attributes applied to lexical variables no longer leak memory.
1861[perl #114764]
1862
1863=item *
1864
1865C<dump>, C<goto>, C<last>, C<next>, C<redo> or C<require> followed by a
1866bareword (or version) and then an infix operator is no longer a syntax
1867error. It used to be for those infix operators (like C<+>) that have a
1868different meaning where a term is expected. [perl #105924]
1869
1870=item *
1871
1872C<require a::b . 1> and C<require a::b + 1> no longer produce erroneous
1873ambiguity warnings. [perl #107002]
1874
1875=item *
1876
1877Class method calls are now allowed on any string, and not just strings
1878beginning with an alphanumeric character. [perl #105922]
1879
1880=item *
1881
1882An empty pattern created with C<qr//> used in C<m///> no longer triggers
1883the "empty pattern reuses last pattern" behaviour. [perl #96230]
1884
1885=item *
1886
1887Tying a hash during iteration no longer results in a memory leak.
1888
1889=item *
1890
1891Freeing a tied hash during iteration no longer results in a memory leak.
1892
1893=item *
1894
1895List assignment to a tied array or hash that dies on STORE no longer
1896results in a memory leak.
1897
1898=item *
1899
1900If the hint hash (C<%^H>) is tied, compile-time scope entry (which copies
1901the hint hash) no longer leaks memory if FETCH dies. [perl #107000]
1902
1903=item *
1904
1905Constant folding no longer inappropriately triggers the special
1906C<split " "> behaviour. [perl #94490]
1907
1908=item *
1909
1910C<defined scalar(@array)>, C<defined do { &foo }>, and similar constructs
1911now treat the argument to C<defined> as a simple scalar. [perl #97466]
1912
1913=item *
1914
1915Running a custom debugging that defines no C<*DB::DB> glob or provides a
1916subroutine stub for C<&DB::DB> no longer results in a crash, but an error
1917instead. [perl #114990]
1918
1919=item *
1920
1921C<reset ""> now matches its documentation. C<reset> only resets C<m?...?>
1922patterns when called with no argument. An empty string for an argument now
1923does nothing. (It used to be treated as no argument.) [perl #97958]
1924
1925=item *
1926
1927C<printf> with an argument returning an empty list no longer reads past the
1928end of the stack, resulting in erratic behaviour. [perl #77094]
1929
1930=item *
1931
1932C<--subname> no longer produces erroneous ambiguity warnings.
1933[perl #77240]
1934
1935=item *
1936
1937C<v10> is now allowed as a label or package name. This was inadvertently
e612b5a0 1938broken when v-strings were added in Perl v5.6. [perl #56880]
5ed58cbd
RS
1939
1940=item *
1941
1942C<length>, C<pos>, C<substr> and C<sprintf> could be confused by ties,
1943overloading, references and typeglobs if the stringification of such
be12dd22 1944changed the internal representation to or from UTF-8. [perl #114410]
5ed58cbd
RS
1945
1946=item *
1947
1948utf8::encode now calls FETCH and STORE on tied variables. utf8::decode now
1949calls STORE (it was already calling FETCH).
1950
1951=item *
1952
1953C<$tied =~ s/$non_utf8/$utf8/> no longer loops infinitely if the tied
1954variable returns a Latin-1 string, shared hash key scalar, or reference or
2ae351f8 1955typeglob that stringifies as ASCII or Latin-1. This was a regression from
e612b5a0 1956v5.12.
5ed58cbd
RS
1957
1958=item *
1959
1960C<s///> without /e is now better at detecting when it needs to forego
1961certain optimisations, fixing some buggy cases:
1962
1963=over
1964
1965=item *
1966
1967Match variables in certain constructs (C<&&>, C<||>, C<..> and others) in
1968the replacement part; e.g., C<s/(.)/$l{$a||$1}/g>. [perl #26986]
1969
1970=item *
1971
1972Aliases to match variables in the replacement.
1973
1974=item *
1975
1976C<$REGERROR> or C<$REGMARK> in the replacement. [perl #49190]
1977
1978=item *
1979
1980An empty pattern (C<s//$foo/>) that causes the last-successful pattern to
1981be used, when that pattern contains code blocks that modify the variables
1982in the replacement.
1983
1984=back
1985
1986=item *
1987
1988The taintedness of the replacement string no longer affects the taintedness
1989of the return value of C<s///e>.
1990
1991=item *
1992
1993The C<$|> autoflush variable is created on-the-fly when needed. If this
1994happened (e.g., if it was mentioned in a module or eval) when the
1995currently-selected filehandle was a typeglob with an empty IO slot, it used
1996to crash. [perl #115206]
1997
1998=item *
1999
2000Line numbers at the end of a string eval are no longer off by one.
2001[perl #114658]
2002
2003=item *
2004
2005@INC filters (subroutines returned by subroutines in @INC) that set $_ to a
2006copy-on-write scalar no longer cause the parser to modify that string
2007buffer in place.
2008
2009=item *
2010
2011C<length($object)> no longer returns the undefined value if the object has
2012string overloading that returns undef. [perl #115260]
2013
2014=item *
2015
2016The use of C<PL_stashcache>, the stash name lookup cache for method calls, has
2017been restored,
2018
2019Commit da6b625f78f5f133 in August 2011 inadvertently broke the code that looks
2020up values in C<PL_stashcache>. As it's a only cache, quite correctly everything
2021carried on working without it.
2022
2023=item *
2024
e612b5a0 2025The error "Can't localize through a reference" had disappeared in v5.16.0
5ed58cbd 2026when C<local %$ref> appeared on the last line of an lvalue subroutine.
e612b5a0 2027This error disappeared for C<\local %$ref> in perl v5.8.1. It has now
5ed58cbd
RS
2028been restored.
2029
2030=item *
2031
2032The parsing of here-docs has been improved significantly, fixing several
2033parsing bugs and crashes and one memory leak, and correcting wrong
2034subsequent line numbers under certain conditions.
2035
2036=item *
2037
2038Inside an eval, the error message for an unterminated here-doc no longer
2039has a newline in the middle of it [perl #70836].
2040
2041=item *
2042
2043A substitution inside a substitution pattern (C<s/${s|||}//>) no longer
2044confuses the parser.
2045
2046=item *
2047
2048It may be an odd place to allow comments, but C<s//"" # hello/e> has
2049always worked, I<unless> there happens to be a null character before the
2050first #. Now it works even in the presence of nulls.
2051
2052=item *
2053
2054An invalid range in C<tr///> or C<y///> no longer results in a memory leak.
2055
2056=item *
2057
2058String eval no longer treats a semicolon-delimited quote-like operator at
2059the very end (C<eval 'q;;'>) as a syntax error.
2060
2061=item *
2062
2063C<< warn {$_ => 1} + 1 >> is no longer a syntax error. The parser used to
2064get confused with certain list operators followed by an anonymous hash and
2065then an infix operator that shares its form with a unary operator.
2066
2067=item *
2068
2069C<(caller $n)[6]> (which gives the text of the eval) used to return the
2070actual parser buffer. Modifying it could result in crashes. Now it always
2071returns a copy. The string returned no longer has "\n;" tacked on to the
2072end. The returned text also includes here-doc bodies, which used to be
2073omitted.
2074
2075=item *
2076
be12dd22
RS
2077Reset the UTF-8 position cache when accessing magical variables to avoid the
2078string buffer and the UTF-8 position cache getting out of sync
5ed58cbd
RS
2079[perl #114410].
2080
2081=item *
2082
be12dd22
RS
2083Various cases of get magic being called twice for magical UTF-8
2084strings have been fixed.
5ed58cbd
RS
2085
2086=item *
2087
2088This code (when not in the presence of C<$&> etc)
2089
2090 $_ = 'x' x 1_000_000;
2091 1 while /(.)/;
2092
2093used to skip the buffer copy for performance reasons, but suffered from C<$1>
2094etc changing if the original string changed. That's now been fixed.
2095
2096=item *
2097
2098Perl doesn't use PerlIO anymore to report out of memory messages, as PerlIO
2099might attempt to allocate more memory.
2100
2101=item *
2102
2103In a regular expression, if something is quantified with C<{n,m}> where
2104C<S<n E<gt> m>>, it can't possibly match. Previously this was a fatal
2105error, but now is merely a warning (and that something won't match).
2106[perl #82954].
2107
2108=item *
2109
2110It used to be possible for formats defined in subroutines that have
2111subsequently been undefined and redefined to close over variables in the
2112wrong pad (the newly-defined enclosing sub), resulting in crashes or
2113"Bizarre copy" errors.
2114
2115=item *
2116
2117Redefinition of XSUBs at run time could produce warnings with the wrong
2118line number.
2119
2120=item *
2121
2122The %vd sprintf format does not support version objects for alpha versions.
2123It used to output the format itself (%vd) when passed an alpha version, and
2124also emit an "Invalid conversion in printf" warning. It no longer does,
2125but produces the empty string in the output. It also no longer leaks
2126memory in this case.
2127
2128=item *
2129
2130C<< $obj->SUPER::method >> calls in the main package could fail if the
2131SUPER package had already been accessed by other means.
2132
2133=item *
2134
f105b7be 2135Stash aliasing (C<< *foo:: = *bar:: >>) no longer causes SUPER calls to ignore
5ed58cbd
RS
2136changes to methods or @ISA or use the wrong package.
2137
2138=item *
2139
2140Method calls on packages whose names end in ::SUPER are no longer treated
2141as SUPER method calls, resulting in failure to find the method.
2142Furthermore, defining subroutines in such packages no longer causes them to
2143be found by SUPER method calls on the containing package [perl #114924].
2144
2145=item *
2146
2147C<\w> now matches the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D
2148(ZERO WIDTH JOINER). C<\W> no longer matches these. This change is because
2149Unicode corrected their definition of what C<\w> should match.
2150
2151=item *
2152
2153C<dump LABEL> no longer leaks its label.
2154
2155=item *
2156
2157Constant folding no longer changes the behaviour of functions like C<stat()>
2158and C<truncate()> that can take either filenames or handles.
2159C<stat 1 ? foo : bar> nows treats its argument as a file name (since it is an
2160arbitrary expression), rather than the handle "foo".
2161
2162=item *
2163
2164C<truncate FOO, $len> no longer falls back to treating "FOO" as a file name if
e612b5a0 2165the filehandle has been deleted. This was broken in Perl v5.16.0.
5ed58cbd
RS
2166
2167=item *
2168
2169Subroutine redefinitions after sub-to-glob and glob-to-glob assignments no
2170longer cause double frees or panic messages.
2171
2172=item *
2173
2174C<s///> now turns vstrings into plain strings when performing a substitution,
2175even if the resulting string is the same (C<s/a/a/>).
2176
2177=item *
2178
2179Prototype mismatch warnings no longer erroneously treat constant subs as having
2180no prototype when they actually have "".
2181
2182=item *
2183
2184Constant subroutines and forward declarations no longer prevent prototype
2185mismatch warnings from omitting the sub name.
2186
2187=item *
2188
2189C<undef> on a subroutine now clears call checkers.
2190
2191=item *
2192
e612b5a0 2193The C<ref> operator started leaking memory on blessed objects in Perl v5.16.0.
5ed58cbd
RS
2194This has been fixed [perl #114340].
2195
2196=item *
2197
2198C<use> no longer tries to parse its arguments as a statement, making
2199C<use constant { () };> a syntax error [perl #114222].
2200
2201=item *
2202
2203On debugging builds, "uninitialized" warnings inside formats no longer cause
2204assertion failures.
2205
2206=item *
2207
2208On debugging builds, subroutines nested inside formats no longer cause
2209assertion failures [perl #78550].
2210
2211=item *
2212
2213Formats and C<use> statements are now permitted inside formats.
2214
2215=item *
2216
2217C<print $x> and C<sub { print $x }-E<gt>()> now always produce the same output.
2218It was possible for the latter to refuse to close over $x if the variable was
2219not active; e.g., if it was defined outside a currently-running named
2220subroutine.
2221
2222=item *
2223
2224Similarly, C<print $x> and C<print eval '$x'> now produce the same output.
2225This also allows "my $x if 0" variables to be seen in the debugger [perl
2226#114018].
2227
2228=item *
2229
2230Formats called recursively no longer stomp on their own lexical variables, but
2231each recursive call has its own set of lexicals.
2232
2233=item *
2234
2235Attempting to free an active format or the handle associated with it no longer
2236results in a crash.
2237
2238=item *
2239
2240Format parsing no longer gets confused by braces, semicolons and low-precedence
2241operators. It used to be possible to use braces as format delimiters (instead
2242of C<=> and C<.>), but only sometimes. Semicolons and low-precedence operators
2243in format argument lines no longer confuse the parser into ignoring the line's
2244return value. In format argument lines, braces can now be used for anonymous
2245hashes, instead of being treated always as C<do> blocks.
2246
2247=item *
2248
2249Formats can now be nested inside code blocks in regular expressions and other
2250quoted constructs (C</(?{...})/> and C<qq/${...}/>) [perl #114040].
2251
2252=item *
2253
2254Formats are no longer created after compilation errors.
2255
2256=item *
2257
2258Under debugging builds, the B<-DA> command line option started crashing in Perl
e612b5a0 2259v5.16.0. It has been fixed [perl #114368].
5ed58cbd
RS
2260
2261=item *
2262
2263A potential deadlock scenario involving the premature termination of a pseudo-
2264forked child in a Windows build with ithreads enabled has been fixed. This
2265resolves the common problem of the F<t/op/fork.t> test hanging on Windows [perl
2266#88840].
2267
2268=item *
2269
5ed58cbd
RS
2270The code which generates errors from C<require()> could potentially read one or
2271two bytes before the start of the filename for filenames less than three bytes
2272long and ending C</\.p?\z/>. This has now been fixed. Note that it could
2273never have happened with module names given to C<use()> or C<require()> anyway.
2274
2275=item *
2276
2277The handling of pathnames of modules given to C<require()> has been made
2278thread-safe on VMS.
2279
2280=item *
2281
d85cd26b
RS
2282Non-blocking sockets have been fixed on VMS.
2283
2284=item *
2285
5ed58cbd
RS
2286A bug in the compilation of a C</(?{})/> expression which affected the TryCatch
2287test suite has been fixed [perl #114242].
2288
2289=item *
2290
2291Pod can now be nested in code inside a quoted construct outside of a string
2292eval. This used to work only within string evals [perl #114040].
2293
2294=item *
2295
2296C<goto ''> now looks for an empty label, producing the "goto must have
2297label" error message, instead of exiting the program [perl #111794].
2298
2299=item *
2300
2301C<goto "\0"> now dies with "Can't find label" instead of "goto must have
2302label".
2303
2304=item *
2305
2306The C function C<hv_store> used to result in crashes when used on C<%^H>
2307[perl #111000].
2308
2309=item *
2310
2311A call checker attached to a closure prototype via C<cv_set_call_checker>
2312is now copied to closures cloned from it. So C<cv_set_call_checker> now
2313works inside an attribute handler for a closure.
2314
2315=item *
2316
2317Writing to C<$^N> used to have no effect. Now it croaks with "Modification
2318of a read-only value" by default, but that can be overridden by a custom
2319regular expression engine, as with C<$1> [perl #112184].
2320
2321=item *
2322
2323C<undef> on a control character glob (C<undef *^H>) no longer emits an
2324erroneous warning about ambiguity [perl #112456].
2325
2326=item *
2327
2328For efficiency's sake, many operators and built-in functions return the
2329same scalar each time. Lvalue subroutines and subroutines in the CORE::
2330namespace were allowing this implementation detail to leak through.
2331C<print &CORE::uc("a"), &CORE::uc("b")> used to print "BB". The same thing
2332would happen with an lvalue subroutine returning the return value of C<uc>.
2333Now the value is copied in such cases.
2334
2335=item *
2336
2337C<method {}> syntax with an empty block or a block returning an empty list
2338used to crash or use some random value left on the stack as its invocant.
2339Now it produces an error.
2340
2341=item *
2342
2343C<vec> now works with extremely large offsets (E<gt>2 GB) [perl #111730].
2344
2345=item *
2346
2347Changes to overload settings now take effect immediately, as do changes to
2348inheritance that affect overloading. They used to take effect only after
2349C<bless>.
2350
2351Objects that were created before a class had any overloading used to remain
2352non-overloaded even if the class gained overloading through C<use overload>
2353or @ISA changes, and even after C<bless>. This has been fixed
2354[perl #112708].
2355
2356=item *
2357
2358Classes with overloading can now inherit fallback values.
2359
2360=item *
2361
2362Overloading was not respecting a fallback value of 0 if there were
2363overloaded objects on both sides of an assignment operator like C<+=>
2364[perl #111856].
2365
2366=item *
2367
2368C<pos> now croaks with hash and array arguments, instead of producing
2369erroneous warnings.
2370
2371=item *
2372
2373C<while(each %h)> now implies C<while(defined($_ = each %h))>, like
2374C<readline> and C<readdir>.
2375
2376=item *
2377
2378Subs in the CORE:: namespace no longer crash after C<undef *_> when called
2379with no argument list (C<&CORE::time> with no parentheses).
2380
2381=item *
2382
2383C<unpack> no longer produces the "'/' must follow a numeric type in unpack"
2384error when it is the data that are at fault [perl #60204].
2385
2386=item *
2387
2388C<join> and C<"@array"> now call FETCH only once on a tied C<$">
2389[perl #8931].
2390
2391=item *
2392
2393Some subroutine calls generated by compiling core ops affected by a
2394C<CORE::GLOBAL> override had op checking performed twice. The checking
2395is always idempotent for pure Perl code, but the double checking can
2396matter when custom call checkers are involved.
2397
2398=item *
2399
2400A race condition used to exist around fork that could cause a signal sent to
2401the parent to be handled by both parent and child. Signals are now blocked
2402briefly around fork to prevent this from happening [perl #82580].
2403
2404=item *
2405
2406The implementation of code blocks in regular expressions, such as C<(?{})>
2407and C<(??{})>, has been heavily reworked to eliminate a whole slew of bugs.
2408The main user-visible changes are:
2409
2410=over 4
2411
2412=item *
2413
2414Code blocks within patterns are now parsed in the same pass as the
2415surrounding code; in particular it is no longer necessary to have balanced
2416braces: this now works:
2417
2418 /(?{ $x='{' })/
2419
2420This means that this error message is no longer generated:
2421
2422 Sequence (?{...}) not terminated or not {}-balanced in regex
2423
2424but a new error may be seen:
2425
2426 Sequence (?{...}) not terminated with ')'
2427
2428In addition, literal code blocks within run-time patterns are only
2429compiled once, at perl compile-time:
2430
2431 for my $p (...) {
2432 # this 'FOO' block of code is compiled once,
2433 # at the same time as the surrounding 'for' loop
2434 /$p{(?{FOO;})/;
2435 }
2436
2437=item *
2438
2439Lexical variables are now sane as regards scope, recursion and closure
2440behavior. In particular, C</A(?{B})C/> behaves (from a closure viewpoint)
2441exactly like C</A/ && do { B } && /C/>, while C<qr/A(?{B})C/> is like
2442C<sub {/A/ && do { B } && /C/}>. So this code now works how you might
2443expect, creating three regexes that match 0, 1, and 2:
2444
2445 for my $i (0..2) {
2446 push @r, qr/^(??{$i})$/;
2447 }
2448 "1" =~ $r[1]; # matches
2449
2450=item *
2451
2452The C<use re 'eval'> pragma is now only required for code blocks defined
2453at runtime; in particular in the following, the text of the C<$r> pattern is
2454still interpolated into the new pattern and recompiled, but the individual
2455compiled code-blocks within C<$r> are reused rather than being recompiled,
2456and C<use re 'eval'> isn't needed any more:
2457
2458 my $r = qr/abc(?{....})def/;
2459 /xyz$r/;
2460
2461=item *
2462
2463Flow control operators no longer crash. Each code block runs in a new
2464dynamic scope, so C<next> etc. will not see
2465any enclosing loops. C<return> returns a value
2466from the code block, not from any enclosing subroutine.
2467
2468=item *
2469
2470Perl normally caches the compilation of run-time patterns, and doesn't
2471recompile if the pattern hasn't changed, but this is now disabled if
2472required for the correct behavior of closures. For example:
2473
2474 my $code = '(??{$x})';
2475 for my $x (1..3) {
2476 # recompile to see fresh value of $x each time
2477 $x =~ /$code/;
2478 }
2479
2480=item *
2481
2482The C</msix> and C<(?msix)> etc. flags are now propagated into the return
2483value from C<(??{})>; this now works:
2484
2485 "AB" =~ /a(??{'b'})/i;
2486
2487=item *
2488
2489Warnings and errors will appear to come from the surrounding code (or for
2490run-time code blocks, from an eval) rather than from an C<re_eval>:
2491
2492 use re 'eval'; $c = '(?{ warn "foo" })'; /$c/;
2493 /(?{ warn "foo" })/;
2494
2495formerly gave:
2496
2497 foo at (re_eval 1) line 1.
2498 foo at (re_eval 2) line 1.
2499
2500and now gives:
2501
2502 foo at (eval 1) line 1.
2503 foo at /some/prog line 2.
2504
2505=back
2506
2507=item *
2508
2e7bc647
KW
2509Perl now can be recompiled to use any Unicode version. In v5.16, it
2510worked on Unicodes 6.0 and 6.1, but there were various bugs if earlier
2511releases were used; the older the release the more problems.
5ed58cbd
RS
2512
2513=item *
2514
2515C<vec> no longer produces "uninitialized" warnings in lvalue context
2516[perl #9423].
2517
2518=item *
2519
2520An optimization involving fixed strings in regular expressions could cause
2521a severe performance penalty in edge cases. This has been fixed
2522[perl #76546].
2523
2524=item *
2525
2526In certain cases, including empty subpatterns within a regular expression (such
2527as C<(?:)> or C<(?:|)>) could disable some optimizations. This has been fixed.
2528
2529=item *
2530
2531The "Can't find an opnumber" message that C<prototype> produces when passed
2532a string like "CORE::nonexistent_keyword" now passes UTF-8 and embedded
2533NULs through unchanged [perl #97478].
2534
2535=item *
2536
2537C<prototype> now treats magical variables like C<$1> the same way as
2538non-magical variables when checking for the CORE:: prefix, instead of
2539treating them as subroutine names.
2540
2541=item *
2542
2543Under threaded perls, a runtime code block in a regular expression could
2544corrupt the package name stored in the op tree, resulting in bad reads
2545in C<caller>, and possibly crashes [perl #113060].
2546
2547=item *
2548
2549Referencing a closure prototype (C<\&{$_[1]}> in an attribute handler for a
2550closure) no longer results in a copy of the subroutine (or assertion
2551failures on debugging builds).
2552
2553=item *
2554
2555C<eval '__PACKAGE__'> now returns the right answer on threaded builds if
2556the current package has been assigned over (as in
2557C<*ThisPackage:: = *ThatPackage::>) [perl #78742].
2558
2559=item *
2560
2561If a package is deleted by code that it calls, it is possible for C<caller>
2562to see a stack frame belonging to that deleted package. C<caller> could
2563crash if the stash's memory address was reused for a scalar and a
2564substitution was performed on the same scalar [perl #113486].
2565
2566=item *
2567
2568C<UNIVERSAL::can> no longer treats its first argument differently
2569depending on whether it is a string or number internally.
2570
2571=item *
2572
2573C<open> with C<< <& >> for the mode checks to see whether the third argument is
2574a number, in determining whether to treat it as a file descriptor or a handle
2575name. Magical variables like C<$1> were always failing the numeric check and
2576being treated as handle names.
2577
2578=item *
2579
2580C<warn>'s handling of magical variables (C<$1>, ties) has undergone several
2581fixes. C<FETCH> is only called once now on a tied argument or a tied C<$@>
2582[perl #97480]. Tied variables returning objects that stringify as "" are
2583no longer ignored. A tied C<$@> that happened to return a reference the
2584I<previous> time it was used is no longer ignored.
2585
2586=item *
2587
2588C<warn ""> now treats C<$@> with a number in it the same way, regardless of
2589whether it happened via C<$@=3> or C<$@="3">. It used to ignore the
2590former. Now it appends "\t...caught", as it has always done with
2591C<$@="3">.
2592
2593=item *
2594
2595Numeric operators on magical variables (e.g., S<C<$1 + 1>>) used to use
2596floating point operations even where integer operations were more appropriate,
2597resulting in loss of accuracy on 64-bit platforms [perl #109542].
2598
2599=item *
2600
2601Unary negation no longer treats a string as a number if the string happened
2602to be used as a number at some point. So, if C<$x> contains the string "dogs",
2603C<-$x> returns "-dogs" even if C<$y=0+$x> has happened at some point.
2604
2605=item *
2606
e612b5a0 2607In Perl v5.14, C<-'-10'> was fixed to return "10", not "+10". But magical
5ed58cbd
RS
2608variables (C<$1>, ties) were not fixed till now [perl #57706].
2609
2610=item *
2611
2612Unary negation now treats strings consistently, regardless of the internal
2613C<UTF8> flag.
2614
2615=item *
2616
2617A regression introduced in Perl v5.16.0 involving
2618C<tr/I<SEARCHLIST>/I<REPLACEMENTLIST>/> has been fixed. Only the first
2619instance is supposed to be meaningful if a character appears more than
2620once in C<I<SEARCHLIST>>. Under some circumstances, the final instance
2621was overriding all earlier ones. [perl #113584]
2622
2623=item *
2624
2625Regular expressions like C<qr/\87/> previously silently inserted a NUL
2626character, thus matching as if it had been written C<qr/\00087/>. Now it
2627matches as if it had been written as C<qr/87/>, with a message that the
2628sequence C<"\8"> is unrecognized.
2629
2630=item *
2631
2632C<__SUB__> now works in special blocks (C<BEGIN>, C<END>, etc.).
2633
2634=item *
2635
2636Thread creation on Windows could theoretically result in a crash if done
2637inside a C<BEGIN> block. It still does not work properly, but it no longer
2638crashes [perl #111610].
2639
2640=item *
2641
2642C<\&{''}> (with the empty string) now autovivifies a stub like any other
2643sub name, and no longer produces the "Unable to create sub" error
2644[perl #94476].
2645
2646=item *
2647
2648A regression introduced in v5.14.0 has been fixed, in which some calls
2649to the C<re> module would clobber C<$_> [perl #113750].
2650
2651=item *
2652
2653C<do FILE> now always either sets or clears C<$@>, even when the file can't be
2654read. This ensures that testing C<$@> first (as recommended by the
2655documentation) always returns the correct result.
2656
2657=item *
2658
2659The array iterator used for the C<each @array> construct is now correctly
2660reset when C<@array> is cleared (RT #75596). This happens for example when the
2661array is globally assigned to, as in C<@array = (...)>, but not when its
2662B<values> are assigned to. In terms of the XS API, it means that C<av_clear()>
2663will now reset the iterator.
2664
2665This mirrors the behaviour of the hash iterator when the hash is cleared.
2666
2667=item *
2668
2669C<< $class->can >>, C<< $class->isa >>, and C<< $class->DOES >> now return
2670correct results, regardless of whether that package referred to by C<$class>
2671exists [perl #47113].
2672
2673=item *
2674
2675Arriving signals no longer clear C<$@> [perl #45173].
2676
2677=item *
2678
2679Allow C<my ()> declarations with an empty variable list [perl #113554].
2680
2681=item *
2682
2683During parsing, subs declared after errors no longer leave stubs
2684[perl #113712].
2685
2686=item *
2687
2688Closures containing no string evals no longer hang on to their containing
2689subroutines, allowing variables closed over by outer subroutines to be
2690freed when the outer sub is freed, even if the inner sub still exists
2691[perl #89544].
2692
2693=item *
2694
2695Duplication of in-memory filehandles by opening with a "<&=" or ">&=" mode
e612b5a0 2696stopped working properly in v5.16.0. It was causing the new handle to
5ed58cbd
RS
2697reference a different scalar variable. This has been fixed [perl #113764].
2698
2699=item *
2700
2701C<qr//> expressions no longer crash with custom regular expression engines
2702that do not set C<offs> at regular expression compilation time
2703[perl #112962].
2704
2705=item *
2706
2707C<delete local> no longer crashes with certain magical arrays and hashes
2708[perl #112966].
2709
2710=item *
2711
2712C<local> on elements of certain magical arrays and hashes used not to
2713arrange to have the element deleted on scope exit, even if the element did
2714not exist before C<local>.
2715
2716=item *
2717
2718C<scalar(write)> no longer returns multiple items [perl #73690].
2719
2720=item *
2721
2722String to floating point conversions no longer misparse certain strings under
2723C<use locale> [perl #109318].
2724
2725=item *
2726
2727C<@INC> filters that die no longer leak memory [perl #92252].
2728
2729=item *
2730
2731The implementations of overloaded operations are now called in the correct
2732context. This allows, among other things, being able to properly override
2733C<< <> >> [perl #47119].
2734
2735=item *
2736
2737Specifying only the C<fallback> key when calling C<use overload> now behaves
2738properly [perl #113010].
2739
2740=item *
2741
2742C<< sub foo { my $a = 0; while ($a) { ... } } >> and
2743C<< sub foo { while (0) { ... } } >> now return the same thing [perl #73618].
2744
2745=item *
2746
2747String negation now behaves the same under C<use integer;> as it does
2748without [perl #113012].
2749
2750=item *
2751
2752C<chr> now returns the Unicode replacement character (U+FFFD) for -1,
2753regardless of the internal representation. -1 used to wrap if the argument
2754was tied or a string internally.
2755
2756=item *
2757
2758Using a C<format> after its enclosing sub was freed could crash as of
e612b5a0 2759perl v5.12.0, if the format referenced lexical variables from the outer sub.
5ed58cbd
RS
2760
2761=item *
2762
2763Using a C<format> after its enclosing sub was undefined could crash as of
e612b5a0 2764perl v5.10.0, if the format referenced lexical variables from the outer sub.
5ed58cbd
RS
2765
2766=item *
2767
2768Using a C<format> defined inside a closure, which format references
2769lexical variables from outside, never really worked unless the C<write>
e612b5a0 2770call was directly inside the closure. In v5.10.0 it even started crashing.
5ed58cbd
RS
2771Now the copy of that closure nearest the top of the call stack is used to
2772find those variables.
2773
2774=item *
2775
2776Formats that close over variables in special blocks no longer crash if a
2777stub exists with the same name as the special block before the special
2778block is compiled.
2779
2780=item *
2781
2782The parser no longer gets confused, treating C<eval foo ()> as a syntax
2783error if preceded by C<print;> [perl #16249].
2784
2785=item *
2786
2787The return value of C<syscall> is no longer truncated on 64-bit platforms
2788[perl #113980].
2789
2790=item *
2791
2792Constant folding no longer causes C<print 1 ? FOO : BAR> to print to the
2793FOO handle [perl #78064].
2794
2795=item *
2796
2797C<do subname> now calls the named subroutine and uses the file name it
2798returns, instead of opening a file named "subname".
2799
2800=item *
2801
2802Subroutines looked up by rv2cv check hooks (registered by XS modules) are
2803now taken into consideration when determining whether C<foo bar> should be
2804the sub call C<foo(bar)> or the method call C<< "bar"->foo >>.
2805
2806=item *
2807
2808C<CORE::foo::bar> is no longer treated specially, allowing global overrides
2809to be called directly via C<CORE::GLOBAL::uc(...)> [perl #113016].
2810
2811=item *
2812
2813Calling an undefined sub whose typeglob has been undefined now produces the
2814customary "Undefined subroutine called" error, instead of "Not a CODE
2815reference".
2816
2817=item *
2818
2819Two bugs involving @ISA have been fixed. C<*ISA = *glob_without_array> and
2820C<undef *ISA; @{*ISA}> would prevent future modifications to @ISA from
2821updating the internal caches used to look up methods. The
e612b5a0 2822*glob_without_array case was a regression from Perl v5.12.
5ed58cbd
RS
2823
2824=item *
2825
2826Regular expression optimisations sometimes caused C<$> with C</m> to
2827produce failed or incorrect matches [perl #114068].
2828
2829=item *
2830
2831C<__SUB__> now works in a C<sort> block when the enclosing subroutine is
2832predeclared with C<sub foo;> syntax [perl #113710].
2833
2834=item *
2835
2836Unicode properties only apply to Unicode code points, which leads to
2837some subtleties when regular expressions are matched against
2838above-Unicode code points. There is a warning generated to draw your
2839attention to this. However, this warning was being generated
2840inappropriately in some cases, such as when a program was being parsed.
2841Non-Unicode matches such as C<\w> and C<[:word;]> should not generate the
2842warning, as their definitions don't limit them to apply to only Unicode
2843code points. Now the message is only generated when matching against
2844C<\p{}> and C<\P{}>. There remains a bug, [perl #114148], for the very
2845few properties in Unicode that match just a single code point. The
2846warning is not generated if they are matched against an above-Unicode
2847code point.
2848
2849=item *
2850
2851Uninitialized warnings mentioning hash elements would only mention the
2852element name if it was not in the first bucket of the hash, due to an
2853off-by-one error.
2854
2855=item *
2856
2857A regular expression optimizer bug could cause multiline "^" to behave
2858incorrectly in the presence of line breaks, such that
2859C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].
2860
2861=item *
2862
2863Failed C<fork> in list context no longer corrupts the stack.
2864C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
2865if the C<fork> call failed.
2866
2867=item *
2868
2869Numerous memory leaks have been fixed, mostly involving tied variables that
2870die, regular expression character classes and code blocks, and syntax
2871errors.
2872
2873=item *
2874
2875Assigning a regular expression (C<${qr//}>) to a variable that happens to
2876hold a floating point number no longer causes assertion failures on
2877debugging builds.
2878
2879=item *
2880
2881Assigning a regular expression to a scalar containing a number no longer
f105b7be 2882causes subsequent numification to produce random numbers.
5ed58cbd
RS
2883
2884=item *
2885
2886Assigning a regular expression to a magic variable no longer wipes away the
e612b5a0 2887magic. This was a regression from v5.10.
5ed58cbd
RS
2888
2889=item *
2890
2891Assigning a regular expression to a blessed scalar no longer results in
e612b5a0 2892crashes. This was also a regression from v5.10.
5ed58cbd
RS
2893
2894=item *
2895
2896Regular expression can now be assigned to tied hash and array elements with
2897flattening into strings.
2898
2899=item *
2900
f105b7be 2901Numifying a regular expression no longer results in an uninitialized
5ed58cbd
RS
2902warning.
2903
2904=item *
2905
2906Negative array indices no longer cause EXISTS methods of tied variables to
e612b5a0 2907be ignored. This was a regression from v5.12.
5ed58cbd
RS
2908
2909=item *
2910
2911Negative array indices no longer result in crashes on arrays tied to
2912non-objects.
2913
2914=item *
2915
be12dd22
RS
2916C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF-8 if the
2917left-hand scalar happened to have produced a UTF-8 string the last time
5ed58cbd
RS
2918overloading was invoked.
2919
2920=item *
2921
2922C<goto &sub> now uses the current value of @_, instead of using the array
2923the subroutine was originally called with. This means
2924C<local @_ = (...); goto &sub> now works [perl #43077].
2925
2926=item *
2927
2928If a debugger is invoked recursively, it no longer stomps on its own
2929lexical variables. Formerly under recursion all calls would share the same
2930set of lexical variables [perl #115742].
2931
2932=item *
2933
2934C<*_{ARRAY}> returned from a subroutine no longer spontaneously
2935becomes empty.
2936
2937=back
2938
2939=head1 Known Problems
2940
2941=over 4
2942
2943=item *
2944
7f50b25b 2945There are no known regressions. Please report any bugs you find!
5ed58cbd
RS
2946
2947=back
2948
2949=head1 Acknowledgements
a75569c0 2950
5ed58cbd 2951XXX Generate this with:
a75569c0 2952
5ed58cbd 2953 perl Porting/acknowledgements.pl v5.18.0..HEAD
f5b73711 2954
44691e6f
AB
2955=head1 Reporting Bugs
2956
e08634c5
SH
2957If you find what you think is a bug, you might check the articles recently
2958posted to the comp.lang.perl.misc newsgroup and the perl bug database at
2959http://rt.perl.org/perlbug/ . There may also be information at
2960http://www.perl.org/ , the Perl Home Page.
44691e6f 2961
e08634c5
SH
2962If you believe you have an unreported bug, please run the L<perlbug> program
2963included with your release. Be sure to trim your bug down to a tiny but
2964sufficient test case. Your bug report, along with the output of C<perl -V>,
2965will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
44691e6f
AB
2966
2967If the bug you are reporting has security implications, which make it
e08634c5
SH
2968inappropriate to send to a publicly archived mailing list, then please send it
2969to perl5-security-report@perl.org. This points to a closed subscription
2970unarchived mailing list, which includes all the core committers, who will be
2971able to help assess the impact of issues, figure out a resolution, and help
f9001595 2972co-ordinate the release of patches to mitigate or fix the problem across all
e08634c5
SH
2973platforms on which Perl is supported. Please only use this address for
2974security issues in the Perl core, not for modules independently distributed on
2975CPAN.
44691e6f
AB
2976
2977=head1 SEE ALSO
2978
e08634c5
SH
2979The F<Changes> file for an explanation of how to view exhaustive details on
2980what changed.
44691e6f
AB
2981
2982The F<INSTALL> file for how to build Perl.
2983
2984The F<README> file for general stuff.
2985
2986The F<Artistic> and F<Copying> files for copyright information.
2987
2988=cut