This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
perldelta: add "how to disable" to experimental warnings
[perl5.git] / pod / perldelta.pod
CommitLineData
44691e6f
AB
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
e612b5a0
RS
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
5ed58cbd
RS
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
1ea0ff56
RS
40Since some features (like C<~~> or C<my $_>) now emit experimental warnings,
41and you may want to disable them in code that is also run on perls that do not
42recognize these warning categories, consider using the C<if> pragma like this:
43
44 no if $] >= 5.018, "experimental::feature_name";
45
5ed58cbd
RS
46Existing experimental features may begin emitting these warnings, too. Please
47consult L<perlexperiment> for information on which features are considered
48experimental.
49
50=head2 Hash overhaul
51
e612b5a0 52Changes to the implementation of hashes in perl v5.18.0 will be one of the most
484d8ba1
DG
53visible changes to the behavior of existing code.
54
8e74b2ed 55By default, two distinct hash variables with identical keys and values may now
484d8ba1
DG
56provide their contents in a different order where it was previously identical.
57
58When encountering these changes, the key to cleaning up from them is to accept
59that B<hashes are unordered collections> and to act accordingly.
5ed58cbd
RS
60
61=head3 Hash randomization
62
63The seed used by Perl's hash function is now random. This means that the
64order which keys/values will be returned from functions like C<keys()>,
65C<values()>, and C<each()> will differ from run to run.
66
67This change was introduced to make Perl's hashes more robust to algorithmic
68complexity attacks, and also because we discovered that it exposes hash
69ordering dependency bugs and makes them easier to track down.
70
71Toolchain maintainers might want to invest in additional infrastructure to
72test for things like this. Running tests several times in a row and then
73comparing results will make it easier to spot hash order dependencies in
74code. Authors are strongly encouraged not to expose the key order of
75Perl's hashes to insecure audiences.
76
77Further, every hash has its own iteration order, which should make it much
78more difficult to determine what the current hash seed is.
79
0f2be12f
RS
80=head3 New hash functions
81
e612b5a0 82Perl v5.18 includes support for multiple hash functions, and changed
0f2be12f
RS
83the default (to ONE_AT_A_TIME_HARD), you can choose a different
84algorithm by defining a symbol at compile time. For a current list,
e612b5a0 85consult the F<INSTALL> document. Note that as of Perl v5.18 we can
0f2be12f
RS
86only recommend use of the default or SIPHASH. All the others are
87known to have security issues and are for research purposes only.
5ed58cbd 88
f105b7be 89=head3 PERL_HASH_SEED environment variable now takes a hex value
5ed58cbd 90
484d8ba1
DG
91C<PERL_HASH_SEED> no longer accepts an integer as a parameter;
92instead the value is expected to be a binary value encoded in a hex
93string, such as "0xf5867c55039dc724". This is to make the
94infrastructure support hash seeds of arbitrary lengths, which might
5ed58cbd
RS
95exceed that of an integer. (SipHash uses a 16 byte seed).
96
c40c48bb
RS
97=head3 PERL_PERTURB_KEYS environment variable added
98
f105b7be 99The C<PERL_PERTURB_KEYS> environment variable allows one to control the level of
c40c48bb
RS
100randomization applied to C<keys> and friends.
101
f105b7be 102When C<PERL_PERTURB_KEYS> is 0, perl will not randomize the key order at all. The
c40c48bb
RS
103chance that C<keys> changes due to an insert will be the same as in previous
104perls, basically only when the bucket size is changed.
105
f105b7be 106When C<PERL_PERTURB_KEYS> is 1, perl will randomize keys in a non-repeatable
c40c48bb
RS
107way. The chance that C<keys> changes due to an insert will be very high. This
108is the most secure and default mode.
109
f105b7be
KE
110When C<PERL_PERTURB_KEYS> is 2, perl will randomize keys in a repeatable way.
111Repeated runs of the same program should produce the same output every time.
c40c48bb 112
f105b7be
KE
113C<PERL_HASH_SEED> implies a non-default C<PERL_PERTURB_KEYS> setting. Setting
114C<PERL_HASH_SEED=0> (exactly one 0) implies C<PERL_PERTURB_KEYS=0> (hash key
115randomization disabled); settng C<PERL_HASH_SEED> to any other value implies
116C<PERL_PERTURB_KEYS=2> (deterministic and repeatable hash key randomization).
117Specifying C<PERL_PERTURB_KEYS> explicitly to a different level overrides this
c40c48bb
RS
118behavior.
119
5ed58cbd
RS
120=head3 Hash::Util::hash_seed() now returns a string
121
122Hash::Util::hash_seed() now returns a string instead of an integer. This
123is to make the infrastructure support hash seeds of arbitrary lengths
124which might exceed that of an integer. (SipHash uses a 16 byte seed).
125
126=head3 Output of PERL_HASH_SEED_DEBUG has been changed
127
128The environment variable PERL_HASH_SEED_DEBUG now makes perl show both the
f105b7be 129hash function perl was built with, I<and> the seed, in hex, in use for that
5ed58cbd
RS
130process. Code parsing this output, should it exist, must change to accommodate
131the new format. Example of the new format:
132
133 $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
134 HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f
135
136=head2 Upgrade to Unicode 6.2
137
2e7bc647 138Perl now supports Unicode 6.2. A list of changes from Unicode
5ed58cbd
RS
1396.1 is at L<http://www.unicode.org/versions/Unicode6.2.0>.
140
141=head2 Character name aliases may now include non-Latin1-range characters
142
143It is possible to define your own names for characters for use in
144C<\N{...}>, C<charnames::vianame()>, etc. These names can now be
145comprised of characters from the whole Unicode range. This allows for
146names to be in your native language, and not just English. Certain
147restrictions apply to the characters that may be used (you can't define
148a name that has punctuation in it, for example). See L<charnames/CUSTOM
149ALIASES>.
150
151=head2 New DTrace probes
152
153The following new DTrace probes have been added:
14731ad1 154
337fb649 155=over 4
14731ad1 156
82d98f72 157=item *
14731ad1 158
5ed58cbd
RS
159C<op-entry>
160
161=item *
162
163C<loading-file>
164
165=item *
166
167C<loaded-file>
168
169=back
170
171=head2 C<${^LAST_FH}>
172
173This new variable provides access to the filehandle that was last read.
174This is the handle used by C<$.> and by C<tell> and C<eof> without
175arguments.
176
177=head2 Regular Expression Set Operations
178
179This is an B<experimental> feature to allow matching against the union,
180intersection, etc., of sets of code points, similar to
181L<Unicode::Regex::Set>. It can also be used to extend C</x> processing
182to [bracketed] character classes, and as a replacement of user-defined
183properties, allowing more complex expressions than they do. See
184L<perlrecharclass/Extended Bracketed Character Classes>.
185
186=head2 Lexical subroutines
187
188This new feature is still considered B<experimental>. To enable it:
189
190 use 5.018;
191 no warnings "experimental::lexical_subs";
192 use feature "lexical_subs";
193
194You can now declare subroutines with C<state sub foo>, C<my sub foo>, and
195C<our sub foo>. (C<state sub> requires that the "state" feature be
196enabled, unless you write it as C<CORE::state sub foo>.)
197
198C<state sub> creates a subroutine visible within the lexical scope in which
199it is declared. The subroutine is shared between calls to the outer sub.
200
201C<my sub> declares a lexical subroutine that is created each time the
202enclosing block is entered. C<state sub> is generally slightly faster than
203C<my sub>.
204
205C<our sub> declares a lexical alias to the package subroutine of the same
206name.
207
208For more information, see L<perlsub/Lexical Subroutines>.
209
210=head2 Computed Labels
211
212The loop controls C<next>, C<last> and C<redo>, and the special C<dump>
213operator, now allow arbitrary expressions to be used to compute labels at run
214time. Previously, any argument that was not a constant was treated as the
215empty string.
216
217=head2 More CORE:: subs
218
219Several more built-in functions have been added as subroutines to the
220CORE:: namespace - namely, those non-overridable keywords that can be
221implemented without custom parsers: C<defined>, C<delete>, C<exists>,
222C<glob>, C<pos>, C<protoytpe>, C<scalar>, C<split>, C<study>, and C<undef>.
223
224As some of these have prototypes, C<prototype('CORE::...')> has been
225changed to not make a distinction between overridable and non-overridable
226keywords. This is to make C<prototype('CORE::pos')> consistent with
227C<prototype(&CORE::pos)>.
228
229=head2 C<kill> with negative signal names
230
231C<kill> has always allowed a negative signal number, which kills the
232process group instead of a single process. It has also allowed signal
233names. But it did not behave consistently, because negative signal names
234were treated as 0. Now negative signals names like C<-INT> are supported
235and treated the same way as -2 [perl #112990].
236
237=head1 Security
238
239=head2 C<Storable> security warning in documentation
240
241The documentation for C<Storable> now includes a section which warns readers
242of the danger of accepting Storable documents from untrusted sources. The
243short version is that deserializing certain types of data can lead to loading
244modules and other code execution. This is documented behavior and wanted
245behavior, but this opens an attack vector for malicious entities.
246
247=head2 C<Locale::Maketext> allowed code injection via a malicious template
248
249If users could provide a translation string to Locale::Maketext, this could be
250used to invoke arbitrary Perl subroutines available in the current process.
251
252This has been fixed, but it is still possible to invoke any method provided by
253C<Locale::Maketext> itself or a subclass that you are using. One of these
254methods in turn will invoke the Perl core's C<sprintf> subroutine.
255
256In summary, allowing users to provide translation strings without auditing
257them is a bad idea.
258
259This vulnerability is documented in CVE-2012-6329.
260
261=head2 Avoid calling memset with a negative count
262
263Poorly written perl code that allows an attacker to specify the count to perl's
264C<x> string repeat operator can already cause a memory exhaustion
e612b5a0 265denial-of-service attack. A flaw in versions of perl before v5.15.5 can escalate
5ed58cbd
RS
266that into a heap buffer overrun; coupled with versions of glibc before 2.16, it
267possibly allows the execution of arbitrary code.
268
269The flaw addressed to this commit has been assigned identifier CVE-2012-5195
270and was researched by Tim Brown.
271
272=head1 Incompatible Changes
273
274=head2 See also: hash overhaul
275
276Some of the changes in the L<hash overhaul|/"Hash overhaul"> are not fully
277compatible with previous versions of perl. Please read that section.
278
279=head2 An unknown character name in C<\N{...}> is now a syntax error
280
281Previously, it warned, and the Unicode REPLACEMENT CHARACTER was
282substituted. Unicode now recommends that this situation be a syntax
283error. Also, the previous behavior led to some confusing warnings and
284behaviors, and since the REPLACEMENT CHARACTER has no use other than as
285a stand-in for some unknown character, any code that has this problem is
286buggy.
287
288=head2 Formerly deprecated characters in C<\N{}> character name aliases are now errors.
289
290Since v5.12.0, it has been deprecated to use certain characters in
291user-defined C<\N{...}> character names. These now cause a syntax
292error. For example, it is now an error to begin a name with a digit,
293such as in
294
295 my $undraftable = "\N{4F}"; # Syntax error!
296
297or to have commas anywhere in the name. See L<charnames/CUSTOM ALIASES>
298
299=head2 C<\N{BELL}> now refers to U+1F514 instead of U+0007
300
301Unicode 6.0 reused the name "BELL" for a different code point than it
302traditionally had meant. Since Perl v5.14, use of this name still
303referred to U+0007, but would raise a deprecation warning. Now, "BELL"
304refers to U+1F514, and the name for U+0007 is "ALERT". All the
305functions in L<charnames> have been correspondingly updated.
306
307=head2 New Restrictions in Multi-Character Case-Insensitive Matching in Regular Expression Bracketed Character Classes
308
309Unicode has now withdrawn their previous recommendation for regular
310expressions to automatically handle cases where a single character can
311match multiple characters case-insensitively, for example the letter
312LATIN SMALL LETTER SHARP S and the sequence C<ss>. This is because
313it turns out to be impracticable to do this correctly in all
314circumstances. Because Perl has tried to do this as best it can, it
315will continue to do so. (We are considering an option to turn it off.)
316However, a new restriction is being added on such matches when they
317occur in [bracketed] character classes. People were specifying
318things such as C</[\0-\xff]/i>, and being surprised that it matches the
319two character sequence C<ss> (since LATIN SMALL LETTER SHARP S occurs in
320this range). This behavior is also inconsistent with using a
321property instead of a range: C<\p{Block=Latin1}> also includes LATIN
322SMALL LETTER SHARP S, but C</[\p{Block=Latin1}]/i> does not match C<ss>.
323The new rule is that for there to be a multi-character case-insensitive
324match within a bracketed character class, the character must be
325explicitly listed, and not as an end point of a range. This more
326closely obeys the Principle of Least Astonishment. See
327L<perlrecharclass/Bracketed Character Classes>. Note that a bug [perl
328#89774], now fixed as part of this change, prevented the previous
329behavior from working fully.
330
331=head2 Explicit rules for variable names and identifiers
332
c6c6975e
RS
333Due to an oversight, single character variable names in v5.16 were
334completely unrestricted. This opened the door to several kinds of
335insanity. As of v5.18, these now follow the rules of other identifiers,
336in addition to accepting characters that match the C<\p{POSIX_Punct}>
337property.
5ed58cbd
RS
338
339There are no longer any differences in the parsing of identifiers
340specified as C<$...> or C<${...}>; previously, they were dealt with in
341different parts of the core, and so had slightly different behavior. For
342instance, C<${foo:bar}> was a legal variable name. Since they are now
343both parsed by the same code, that is no longer the case.
344
345=head2 C<\s> in regular expressions now matches a Vertical Tab
346
347No one could recall why C<\s> didn't match C<\cK>, the vertical tab.
348Now it does. Given the extreme rarity of that character, very little
349breakage is expected.
350
351=head2 C</(?{})/> and C</(??{})/> have been heavily reworked
352
353The implementation of this feature has been almost completely rewritten.
354Although its main intent is to fix bugs, some behaviors, especially
355related to the scope of lexical variables, will have changed. This is
356described more fully in the L</Selected Bug Fixes> section.
357
358=head2 Stricter parsing of substitution replacement
359
360It is no longer possible to abuse the way the parser parses C<s///e> like
361this:
362
363 %_=(_,"Just another ");
364 $_="Perl hacker,\n";
365 s//_}->{_/e;print
366
367=head2 C<given> now aliases the global C<$_>
368
369Instead of assigning to an implicit lexical C<$_>, C<given> now makes the
370global C<$_> an alias for its argument, just like C<foreach>. However, it
371still uses lexical C<$_> if there is lexical C<$_> in scope (again, just like
372C<foreach>) [perl #114020].
373
374=head2 Lexical C<$_> is now experimental
375
e612b5a0 376Since it was introduced in Perl v5.10, it has caused much confusion with no
5ed58cbd
RS
377obvious solution:
378
379=over
829397b9
TC
380
381=item *
382
5ed58cbd
RS
383Various modules (e.g., List::Util) expect callback routines to use the
384global C<$_>. C<use List::Util 'first'; my $_; first { $_ == 1 } @list>
385does not work as one would expect.
71e6aba6
RS
386
387=item *
388
5ed58cbd
RS
389A C<my $_> declaration earlier in the same file can cause confusing closure
390warnings.
71e6aba6
RS
391
392=item *
393
5ed58cbd
RS
394The "_" subroutine prototype character allows called subroutines to access
395your lexical C<$_>, so it is not really private after all.
2426c394 396
71e6aba6
RS
397=item *
398
5ed58cbd
RS
399Nevertheless, subroutines with a "(@)" prototype and methods cannot access
400the caller's lexical C<$_>, unless they are written in XS.
71e6aba6
RS
401
402=item *
403
5ed58cbd
RS
404But even XS routines cannot access a lexical C<$_> declared, not in the
405calling subroutine, but in an outer scope, iff that subroutine happened not
406to mention C<$_> or use any operators that default to C<$_>.
407
408=back
409
410It is our hope that lexical C<$_> can be rehabilitated, but this may
411cause changes in its behavior. Please use it with caution until it
412becomes stable.
413
414=head2 readline() with C<$/ = \N> now reads N characters, not N bytes
415
416Previously, when reading from a stream with I/O layers such as
417C<encoding>, the readline() function, otherwise known as the C<< <> >>
418operator, would read I<N> bytes from the top-most layer. [perl #79960]
419
420Now, I<N> characters are read instead.
421
422There is no change in behaviour when reading from streams with no
423extra layers, since bytes map exactly to characters.
424
425=head2 Overridden C<glob> is now passed one argument
426
427C<glob> overrides used to be passed a magical undocumented second argument
428that identified the caller. Nothing on CPAN was using this, and it got in
429the way of a bug fix, so it was removed. If you really need to identify
430the caller, see L<Devel::Callsite> on CPAN.
431
432=head2 Here-doc parsing
433
434The body of a here-document inside a quote-like operator now always begins
435on the line after the "<<foo" marker. Previously, it was documented to
436begin on the line following the containing quote-like operator, but that
437was only sometimes the case [perl #114040].
438
439=head2 Alphanumeric operators must now be separated from the closing
440delimiter of regular expressions
441
442You may no longer write something like:
443
444 m/a/and 1
445
446Instead you must write
447
448 m/a/ and 1
449
450with whitespace separating the operator from the closing delimiter of
451the regular expression. Not having whitespace has resulted in a
452deprecation warning since Perl v5.14.0.
453
454=head2 qw(...) can no longer be used as parentheses
455
456C<qw> lists used to fool the parser into thinking they were always
457surrounded by parentheses. This permitted some surprising constructions
458such as C<foreach $x qw(a b c) {...}>, which should really be written
459C<foreach $x (qw(a b c)) {...}>. These would sometimes get the lexer into
460the wrong state, so they didn't fully work, and the similar C<foreach qw(a
461b c) {...}> that one might expect to be permitted never worked at all.
462
463This side effect of C<qw> has now been abolished. It has been deprecated
e612b5a0 464since Perl v5.13.11. It is now necessary to use real parentheses
5ed58cbd
RS
465everywhere that the grammar calls for them.
466
467=head2 Interaction of lexical and default warnings
468
469Turning on any lexical warnings used first to disable all default warnings
470if lexical warnings were not already enabled:
471
472 $*; # deprecation warning
473 use warnings "void";
474 $#; # void warning; no deprecation warning
475
f105b7be 476Now, the C<debugging>, C<deprecated>, C<glob>, C<inplace> and C<malloc> warnings
5ed58cbd
RS
477categories are left on when turning on lexical warnings (unless they are
478turned off by C<no warnings>, of course).
479
480This may cause deprecation warnings to occur in code that used to be free
481of warnings.
482
483Those are the only categories consisting only of default warnings. Default
f105b7be
KE
484warnings in other categories are still disabled by C<< use warnings "category" >>,
485as we do not yet have the infrastructure for controlling
5ed58cbd
RS
486individual warnings.
487
488=head2 C<state sub> and C<our sub>
489
490Due to an accident of history, C<state sub> and C<our sub> were equivalent
491to a plain C<sub>, so one could even create an anonymous sub with
492C<our sub { ... }>. These are now disallowed outside of the "lexical_subs"
493feature. Under the "lexical_subs" feature they have new meanings described
494in L<perlsub/Lexical Subroutines>.
495
496=head2 Defined values stored in environment are forced to byte strings
497
498A value stored in an environment variable has always been stringified. In this
499release, it is converted to be only a byte string. First, it is forced to be a
500only a string. Then if the string is utf8 and the equivalent of
501C<utf8::downgrade()> works, that result is used; otherwise, the equivalent of
502C<utf8::encode()> is used, and a warning is issued about wide characters
503(L</Diagnostics>).
504
505=head2 C<require> dies for unreadable files
506
507When C<require> encounters an unreadable file, it now dies. It used to
508ignore the file and continue searching the directories in C<@INC>
509[perl #113422].
510
511=head2 C<gv_fetchmeth_*> and SUPER
512
513The various C<gv_fetchmeth_*> XS functions used to treat a package whose
f105b7be
KE
514named ended with C<::SUPER> specially. A method lookup on the C<Foo::SUPER>
515package would be treated as a C<SUPER> method lookup on the C<Foo> package. This
516is no longer the case. To do a C<SUPER> lookup, pass the C<Foo> stash and the
517C<GV_SUPER> flag.
5ed58cbd
RS
518
519=head2 C<split>'s first argument is more consistently interpreted
520
e612b5a0 521After some changes earlier in v5.17, C<split>'s behavior has been
5ed58cbd
RS
522simplified: if the PATTERN argument evaluates to a literal string
523containing one space, it is treated the way that a I<literal> string
524containing one space once was.
525
526=head1 Deprecations
527
528=head2 Deprecated modules
529
530The following modules will be removed from the core distribution in a
531future release, and should be installed from CPAN instead. Distributions
532on CPAN which require these should add them to their prerequisites.
f105b7be 533The core versions of these modules will issue C<"deprecated">-category
5ed58cbd
RS
534warnings.
535
536You can silence these deprecation warnings by installing the modules
537in question from CPAN.
538
539=over
540
541=item L<Archive::Extract>
542
543=item L<B::Lint>
544
545=item L<B::Lint::Debug>
546
547=item L<CPANPLUS> and all included C<CPANPLUS::*> modules
548
549=item L<Devel::InnerPackage>
550
551=item L<encoding>
552
553=item L<Log::Message>
554
555=item L<Log::Message::Config>
556
557=item L<Log::Message::Handlers>
558
559=item L<Log::Message::Item>
560
561=item L<Log::Message::Simple>
562
563=item L<Module::Pluggable>
564
565=item L<Module::Pluggable::Object>
566
567=item L<Object::Accessor>
568
569=item L<Pod::LaTeX>
570
571=item L<Term::UI>
572
573=item L<Term::UI::History>
574
575=back
576
577=head2 Deprecated Utilities
578
579The following utilities will be removed from the core distribution in a
580future release as their associated modules have been deprecated. They
581will remain available with the applicable CPAN distribution.
582
583=over
584
585=item L<cpanp>
586
587=item C<cpanp-run-perl>
588
589=item L<cpan2dist>
590
591These items are part of the C<CPANPLUS> distribution.
592
593=item L<pod2latex>
594
595This item is part of the C<Pod::LaTeX> distribution.
596
597=back
598
599=head2 PL_sv_objcount
600
601This interpreter-global variable used to track the total number of
602Perl objects in the interpreter. It is no longer maintained and will
e612b5a0 603be removed altogether in Perl v5.20.
5ed58cbd
RS
604
605=head2 Five additional characters should be escaped in patterns with C</x>
606
607When a regular expression pattern is compiled with C</x>, Perl treats 6
608characters as white space to ignore, such as SPACE and TAB. However,
609Unicode recommends 11 characters be treated thusly. We will conform
610with this in a future Perl version. In the meantime, use of any of the
611missing characters will raise a deprecation warning, unless turned off.
612The five characters are:
f105b7be
KE
613
614 U+0085 NEXT LINE,
615 U+200E LEFT-TO-RIGHT MARK,
616 U+200F RIGHT-TO-LEFT MARK,
617 U+2028 LINE SEPARATOR,
618
5ed58cbd 619and
f105b7be
KE
620
621 U+2029 PARAGRAPH SEPARATOR.
5ed58cbd
RS
622
623=head2 User-defined charnames with surprising whitespace
624
625A user-defined character name with trailing or multiple spaces in a row is
626likely a typo. This now generates a warning when defined, on the assumption
627that uses of it will be unlikely to include the excess whitespace.
628
629=head2 Various XS-callable functions are now deprecated
630
631All the functions used to classify characters will be removed from a
632future version of Perl, and should not be used. With participating C
633compilers (e.g., gcc), compiling any file that uses any of these will
634generate a warning. These were not intended for public use; there are
635equivalent, faster, macros for most of them.
e612b5a0 636
2e7bc647 637See L<perlapi/Character classes>. The complete list is:
e612b5a0 638
5ed58cbd
RS
639C<is_uni_alnum>, C<is_uni_alnumc>, C<is_uni_alnumc_lc>,
640C<is_uni_alnum_lc>, C<is_uni_alpha>, C<is_uni_alpha_lc>,
641C<is_uni_ascii>, C<is_uni_ascii_lc>, C<is_uni_blank>,
642C<is_uni_blank_lc>, C<is_uni_cntrl>, C<is_uni_cntrl_lc>,
643C<is_uni_digit>, C<is_uni_digit_lc>, C<is_uni_graph>,
644C<is_uni_graph_lc>, C<is_uni_idfirst>, C<is_uni_idfirst_lc>,
645C<is_uni_lower>, C<is_uni_lower_lc>, C<is_uni_print>,
646C<is_uni_print_lc>, C<is_uni_punct>, C<is_uni_punct_lc>,
647C<is_uni_space>, C<is_uni_space_lc>, C<is_uni_upper>,
648C<is_uni_upper_lc>, C<is_uni_xdigit>, C<is_uni_xdigit_lc>,
649C<is_utf8_alnum>, C<is_utf8_alnumc>, C<is_utf8_alpha>,
650C<is_utf8_ascii>, C<is_utf8_blank>, C<is_utf8_char>,
651C<is_utf8_cntrl>, C<is_utf8_digit>, C<is_utf8_graph>,
652C<is_utf8_idcont>, C<is_utf8_idfirst>, C<is_utf8_lower>,
653C<is_utf8_mark>, C<is_utf8_perl_space>, C<is_utf8_perl_word>,
654C<is_utf8_posix_digit>, C<is_utf8_print>, C<is_utf8_punct>,
655C<is_utf8_space>, C<is_utf8_upper>, C<is_utf8_xdigit>,
656C<is_utf8_xidcont>, C<is_utf8_xidfirst>.
657
658In addition these three functions that have never worked properly are
659deprecated:
660C<to_uni_lower_lc>, C<to_uni_title_lc>, and C<to_uni_upper_lc>.
661
f105b7be 662=head2 Certain rare uses of backslashes within regexes are now deprecated
5ed58cbd
RS
663
664There are three pairs of characters that Perl recognizes as
665metacharacters in regular expression patterns: C<{}>, C<[]>, and C<()>.
666These can be used as well to delimit patterns, as in:
667
668 m{foo}
669 s(foo)(bar)
670
671Since they are metacharacters, they have special meaning to regular
672expression patterns, and it turns out that you can't turn off that
673special meaning by the normal means of preceding them with a backslash,
f105b7be 674if you use them, paired, within a pattern delimited by them. For
5ed58cbd
RS
675example, in
676
677 m{foo\{1,3\}}
678
679the backslashes do not change the behavior, and this matches
680S<C<"f o">> followed by one to three more occurrences of C<"o">.
681
682Usages like this, where they are interpreted as metacharacters, are
683exceedingly rare; we think there are none, for example, in all of CPAN.
684Hence, this deprecation should affect very little code. It does give
685notice, however, that any such code needs to change, which will in turn
686allow us to change the behavior in future Perl versions so that the
687backslashes do have an effect, and without fear that we are silently
688breaking any existing code.
689
d5f315e8
KW
690=head2 Splitting the tokens C<(?> and C<(*> in regular expressions
691
692A deprecation warning is now raised if the C<(> and C<?> are separated
693by white space or comments in C<(?...)> regular expression constructs.
694Similarly, if the C<(> and C<*> are separated in C<(*VERB...)>
695constructs.
696
e0a1dec5
LT
697=head2 Pre-PerlIO IO implementations
698
699Perl supports being built without PerlIO proper, using a stdio or sfio
700wrapper instead. A perl build like this will not support IO layers and
701thus Unicode IO, making it rather handicapped.
702
703PerlIO supports a C<stdio> layer if stdio use is desired, and similarly a
704sfio layer could be produced.
705
5ed58cbd
RS
706=head1 Future Deprecations
707
708=over
71e6aba6
RS
709
710=item *
711
4263dd11 712Platforms without support infrastructure
5ed58cbd
RS
713
714Both Windows CE and z/OS have been historically under-maintained, and are
715currently neither successfully building nor regularly being smoke tested.
716Efforts are underway to change this situation, but it should not be taken for
717granted that the platforms are safe and supported. If they do not become
718buildable and regularly smoked, support for them may be actively removed in
719future releases. If you have an interest in these platforms and you can lend
720your time, expertise, or hardware to help support these platforms, please let
721the perl development effort know by emailing C<perl5-porters@perl.org>.
722
723Some platforms that appear otherwise entirely dead are also on the short list
e612b5a0 724for removal between now and v5.20.0:
5ed58cbd
RS
725
726=over
727
728=item DG/UX
729
730=item NeXT
731
732=back
1993add8 733
ec985017
RS
734We also think it likely that current versions of Perl will no longer
735build AmigaOS, DJGPP, NetWare (natively), OS/2 and Plan 9. If you
736are using Perl on such a platform and have an interest in ensuring
737Perl's future on them, please contact us.
738
739We believe that Perl has long been unable to build on mixed endian
740architectures (such as PDP-11s), and intend to remove any remain
741support code. Similarly, code supporting the long umaintained GNU
742dld will be removed soon if no-one makes themselves known as an
743active user.
744
1993add8
RS
745=item *
746
5ed58cbd
RS
747Swapping of $< and $>
748
749For more information about this future deprecation, see L<the relevant RT
750ticket|https://rt.perl.org/rt3/Ticket/Display.html?id=96212>.
71e6aba6
RS
751
752=item *
753
5ed58cbd 754C<microperl>, long broken and of unclear present purpose, will be removed.
71e6aba6
RS
755
756=item *
757
5ed58cbd
RS
758Revamping C<< "\Q" >> semantics in double-quotish strings when combined with
759other escapes.
760
761There are several bugs and inconsistencies involving combinations
762of C<\Q> and escapes like C<\x>, C<\L>, etc., within a C<\Q...\E> pair.
763These need to be fixed, and doing so will necessarily change current
764behavior. The changes have not yet been settled.
71e6aba6 765
d5f315e8
KW
766=item *
767
768Use of C<$^>, where C<^> stands for any actual (non-printing) C0 control
769character will be disallowed in a future Perl version. Use C<${^}>
770instead (where again C<^> stands for a control character),
771or better, C<$^A> , where C<^> this time is a caret (CIRCUMFLEX ACCENT),
772and C<A> stands for any of the characters listed at the end of
773L<perlebcdic/OPERATOR DIFFERENCES>.
774
337fb649 775=back
2426c394 776
5ed58cbd
RS
777=head1 Performance Enhancements
778
779=over 4
2426c394 780
5ed58cbd 781=item *
2426c394 782
5ed58cbd
RS
783Lists of lexical variable declarations (C<my($x, $y)>) are now optimised
784down to a single op and are hence faster than before.
2426c394 785
5ed58cbd 786=item *
2426c394 787
5ed58cbd
RS
788A new C preprocessor define C<NO_TAINT_SUPPORT> was added that, if set,
789disables Perl's taint support altogether. Using the -T or -t command
790line flags will cause a fatal error. Beware that both core tests as
791well as many a CPAN distribution's tests will fail with this change. On
792the upside, it provides a small performance benefit due to reduced
793branching.
2426c394 794
5ed58cbd
RS
795B<Do not enable this unless you know exactly what you are getting yourself
796into.>
797
798=item *
799
800C<pack> with constant arguments is now constant folded in most cases
801[perl #113470].
802
803=item *
804
805Speed up in regular expression matching against Unicode properties. The
806largest gain is for C<\X>, the Unicode "extended grapheme cluster." The
807gain for it is about 35% - 40%. Bracketed character classes, e.g.,
808C<[0-9\x{100}]> containing code points above 255 are also now faster.
809
810=item *
811
812On platforms supporting it, several former macros are now implemented as static
813inline functions. This should speed things up slightly on non-GCC platforms.
814
815=item *
816
66f62cf6
RS
817The optimisation of hashes in boolean context has been extended to
818affect C<scalar(%hash)>, C<%hash ? ... : ...>, and C<sub { %hash || ... }>.
5ed58cbd
RS
819
820=item *
821
f105b7be 822Filetest operators manage the stack in a fractionally more efficient manner.
5ed58cbd
RS
823
824=item *
825
826Globs used in a numeric context are now numified directly in most cases,
f105b7be 827rather than being numified via stringification.
5ed58cbd
RS
828
829=item *
830
831The C<x> repetition operator is now folded to a single constant at compile
832time if called in scalar context with constant operands and no parentheses
833around the left operand.
834
835=back
836
837=head1 Modules and Pragmata
838
839=head2 New Modules and Pragmata
2426c394 840
337fb649 841=over 4
982110e0 842
82d98f72 843=item *
2426c394 844
5ed58cbd
RS
845L<Config::Perl::V> version 0.16 has been added as a dual-lifed module.
846It provides structured data retrieval of C<perl -V> output including
847information only known to the C<perl> binary and not available via L<Config>.
848
849=back
850
851=head2 Updated Modules and Pragmata
852
9863976f 853For a complete list of updates, run:
5ed58cbd 854
f105b7be 855 $ corelist --diff 5.16.0 5.18.0
5ed58cbd 856
e612b5a0 857You can substitute your favorite version in place of C<5.16.0>, too.
5ed58cbd 858
5ed58cbd
RS
859=head2 Removed Modules and Pragmata
860
861=over
33392251
BF
862
863=item *
864
5ed58cbd
RS
865L<Version::Requirements> has been removed from the core distribution. It is
866available under a different name: L<CPAN::Meta::Requirements>.
2426c394 867
337fb649 868=back
2426c394 869
5ed58cbd 870=head1 Documentation
19718730 871
5ed58cbd
RS
872=head2 Changes to Existing Documentation
873
874=head3 L<perlcheat>
82d98f72 875
5a6a30f4 876=over 4
b7c7d786 877
5ed58cbd
RS
878=item *
879
880L<perlcheat> has been reorganized, and a few new sections were added.
881
882=back
883
884=head3 L<perldata>
885
886=over 4
82d98f72 887
5ed58cbd 888=item *
d2d1e842 889
5ed58cbd
RS
890Now explicitly documents the behaviour of hash initializer lists that
891contain duplicate keys.
f355e93d 892
5a6a30f4 893=back
f355e93d 894
5ed58cbd 895=head3 L<perldiag>
19718730 896
19718730 897=over 4
e14ac59b 898
5ed58cbd
RS
899=item *
900
901The explanation of symbolic references being prevented by "strict refs"
902now doesn't assume that the reader knows what symbolic references are.
903
904=back
9f351b45 905
5ed58cbd 906=head3 L<perlfaq>
9f351b45 907
5ed58cbd 908=over 4
9f351b45 909
5ed58cbd 910=item *
7cf3104f 911
5ed58cbd 912L<perlfaq> has been synchronized with version 5.0150040 from CPAN.
12719193 913
6253ee75 914=back
216cf7fc 915
5ed58cbd 916=head3 L<perlfunc>
f5b73711 917
5ed58cbd
RS
918=over 4
919
920=item *
a75569c0 921
5ed58cbd 922The return value of C<pipe> is now documented.
a75569c0 923
5ed58cbd 924=item *
a75569c0 925
5ed58cbd
RS
926Clarified documentation of C<our>.
927
928=back
929
930=head3 L<perlop>
931
932=over 4
933
934=item *
935
936Loop control verbs (C<dump>, C<goto>, C<next>, C<last> and C<redo>) have always
937had the same precedence as assignment operators, but this was not documented
938until now.
939
940=back
941
942=head3 Diagnostics
943
944The following additions or changes have been made to diagnostic output,
945including warnings and fatal error messages. For the complete list of
946diagnostic messages, see L<perldiag>.
947
5ed58cbd
RS
948=head2 New Diagnostics
949
5ed58cbd
RS
950=head3 New Errors
951
952=over 4
953
954=item *
955
956L<Unterminated delimiter for here document|perldiag/"Unterminated delimiter for here document">
957
958This message now occurs when a here document label has an initial quotation
959mark but the final quotation mark is missing.
960
961This replaces a bogus and misleading error message about not finding the label
962itself [perl #114104].
963
964=item *
965
966L<panic: child pseudo-process was never scheduled|perldiag/"panic: child pseudo-process was never scheduled">
967
968This error is thrown when a child pseudo-process in the ithreads implementation
969on Windows was not scheduled within the time period allowed and therefore was
970not able to initialize properly [perl #88840].
971
972=item *
973
974L<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/">
975
976This error has been added for C<(?&0)>, which is invalid. It used to
977produce an incomprehensible error message [perl #101666].
978
979=item *
980
981L<Can't use an undefined value as a subroutine reference|perldiag/"Can't use an undefined value as %s reference">
982
983Calling an undefined value as a subroutine now produces this error message.
984It used to, but was accidentally disabled, first in Perl 5.004 for
e612b5a0 985non-magical variables, and then in Perl v5.14 for magical (e.g., tied)
5ed58cbd
RS
986variables. It has now been restored. In the mean time, undef was treated
987as an empty string [perl #113576].
988
989=item *
990
991L<Experimental "%s" subs not enabled|perldiag/"Experimental "%s" subs not enabled">
992
993To use lexical subs, you must first enable them:
994
995 no warnings 'experimental::lexical_subs';
996 use feature 'lexical_subs';
997 my sub foo { ... }
998
999=back
1000
1001=head3 New Warnings
1002
1003=over 4
1004
1005=item *
1006
5ed58cbd
RS
1007Strings with code points over 0xFF may not be mapped into in-memory file
1008handles
1009
1010=item *
1011
1012L<'%s' resolved to '\o{%s}%d'|perldiag/"'%s' resolved to '\o{%s}%d'">
1013
1014=item *
1015
1016L<'Trailing white-space in a charnames alias definition is deprecated'|perldiag/"Trailing white-space in a charnames alias definition is deprecated">
1017
1018=item *
1019
1020L<'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">
1021
1022=item *
1023
1024L<'Passing malformed UTF-8 to "%s" is deprecated'|perldiag/"Passing malformed UTF-8 to "%s" is deprecated">
1025
1026=item *
1027
1028L<Subroutine "&%s" is not available|perldiag/"Subroutine "&%s" is not available">
1029
1030(W closure) During compilation, an inner named subroutine or eval is
1031attempting to capture an outer lexical subroutine that is not currently
1032available. This can happen for one of two reasons. First, the lexical
1033subroutine may be declared in an outer anonymous subroutine that has not
1034yet been created. (Remember that named subs are created at compile time,
1035while anonymous subs are created at run-time.) For example,
1036
1037 sub { my sub a {...} sub f { \&a } }
1038
1039At the time that f is created, it can't capture the current the "a" sub,
1040since the anonymous subroutine hasn't been created yet. Conversely, the
1041following won't give a warning since the anonymous subroutine has by now
1042been created and is live:
1043
1044 sub { my sub a {...} eval 'sub f { \&a }' }->();
1045
1046The second situation is caused by an eval accessing a variable that has
1047gone out of scope, for example,
1048
1049 sub f {
1050 my sub a {...}
1051 sub { eval '\&a' }
1052 }
1053 f()->();
1054
1055Here, when the '\&a' in the eval is being compiled, f() is not currently
1056being executed, so its &a is not available for capture.
1057
1058=item *
1059
1060L<"%s" subroutine &%s masks earlier declaration in same %s|perldiag/"%s" subroutine &%s masks earlier declaration in same %s>
1061
1062(W misc) A "my" or "state" subroutine has been redeclared in the
1063current scope or statement, effectively eliminating all access to
1064the previous instance. This is almost always a typographical error.
1065Note that the earlier subroutine will still exist until the end of
1066the scope or until all closure references to it are destroyed.
1067
1068=item *
1069
1070L<The %s feature is experimental|perldiag/"The %s feature is experimental">
1071
1072(S experimental) This warning is emitted if you enable an experimental
1073feature via C<use feature>. Simply suppress the warning if you want
1074to use the feature, but know that in doing so you are taking the risk
1075of using an experimental feature which may change or be removed in a
1076future Perl version:
1077
1078 no warnings "experimental::lexical_subs";
1079 use feature "lexical_subs";
1080
1081=item *
1082
1083L<sleep(%u) too large|perldiag/"sleep(%u) too large">
1084
1085(W overflow) You called C<sleep> with a number that was larger than it can
1086reliably handle and C<sleep> probably slept for less time than requested.
1087
1088=item *
1089
1090L<Wide character in setenv|perldiag/"Wide character in %s">
1091
1092Attempts to put wide characters into environment variables via C<%ENV> now
1093provoke this warning.
1094
1095=item *
1096
1097"L<Invalid negative number (%s) in chr|perldiag/"Invalid negative number (%s) in chr">"
1098
1099C<chr()> now warns when passed a negative value [perl #83048].
1100
1101=item *
1102
1103"L<Integer overflow in srand|perldiag/"Integer overflow in srand">"
1104
1105C<srand()> now warns when passed a value that doesn't fit in a C<UV> (since the
1106value will be truncated rather than overflowing) [perl #40605].
1107
1108=item *
1109
1110"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">"
1111
1112Running perl with the C<-i> flag now warns if no input files are provided on
1113the command line [perl #113410].
1114
1115=back
1116
1117=head2 Changes to Existing Diagnostics
1118
1119=over 4
1120
1121=item *
1122
1123L<$* is no longer supported|perldiag/"$* is no longer supported">
1124
1125The warning that use of C<$*> and C<$#> is no longer supported is now
1126generated for every location that references them. Previously it would fail
1127to be generated if another variable using the same typeglob was seen first
1128(e.g. C<@*> before C<$*>), and would not be generated for the second and
1129subsequent uses. (It's hard to fix the failure to generate warnings at all
1130without also generating them every time, and warning every time is
1131consistent with the warnings that C<$[> used to generate.)
1132
1133=item *
1134
1135The warnings for C<\b{> and C<\B{> were added. They are a deprecation
1136warning which should be turned off by that category. One should not
1137have to turn off regular regexp warnings as well to get rid of these.
1138
1139=item *
1140
1141L<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>
1142
1143Constant overloading that returns C<undef> results in this error message.
1144For numeric constants, it used to say "Constant(undef)". "undef" has been
1145replaced with the number itself.
1146
1147=item *
1148
1149The error produced when a module cannot be loaded now includes a hint that
1150the module may need to be installed: "Can't locate hopping.pm in @INC (you
1151may need to install the hopping module) (@INC contains: ...)"
1152
1153=item *
1154
1155L<vector argument not supported with alpha versions|perldiag/vector argument not supported with alpha versions>
1156
1157This warning was not suppressable, even with C<no warnings>. Now it is
1158suppressible, and has been moved from the "internal" category to the
1159"printf" category.
1160
1161=item *
1162
1163C<< Can't do {n,m} with n > m in regex; marked by <-- HERE in m/%s/ >>
1164
1165This fatal error has been turned into a warning that reads:
1166
1167L<< Quantifier {n,m} with n > m can't match in regex | perldiag/Quantifier {n,m} with n > m can't match in regex >>
1168
1169(W regexp) Minima should be less than or equal to maxima. If you really want
1170your regexp to match something 0 times, just put {0}.
1171
1172=item *
1173
1174The "Runaway prototype" warning that occurs in bizarre cases has been
1175removed as being unhelpful and inconsistent.
1176
1177=item *
1178
1179The "Not a format reference" error has been removed, as the only case in
1180which it could be triggered was a bug.
1181
1182=item *
1183
1184The "Unable to create sub named %s" error has been removed for the same
1185reason.
1186
1187=item *
1188
1189The 'Can't use "my %s" in sort comparison' error has been downgraded to a
1190warning, '"my %s" used in sort comparison' (with 'state' instead of 'my'
1191for state variables). In addition, the heuristics for guessing whether
1192lexical $a or $b has been misused have been improved to generate fewer
1193false positives. Lexical $a and $b are no longer disallowed if they are
1194outside the sort block. Also, a named unary or list operator inside the
1195sort block no longer causes the $a or $b to be ignored [perl #86136].
1196
1197=back
1198
1199=head1 Utility Changes
1200
1201=head3 L<h2xs>
1202
1203=over 4
1204
1205=item *
1206
1207F<h2xs> no longer produces invalid code for empty defines. [perl #20636]
1208
1209=back
1210
1211=head1 Configuration and Compilation
1212
1213=over 4
1214
1215=item *
1216
1217Added C<useversionedarchname> option to Configure
1218
1219When set, it includes 'api_versionstring' in 'archname'. E.g.
1220x86_64-linux-5.13.6-thread-multi. It is unset by default.
1221
1222This feature was requested by Tim Bunce, who observed that
f105b7be 1223C<INSTALL_BASE> creates a library structure that does not
5ed58cbd
RS
1224differentiate by perl version. Instead, it places architecture
1225specific files in "$install_base/lib/perl5/$archname". This makes
f105b7be 1226it difficult to use a common C<INSTALL_BASE> library path with
5ed58cbd
RS
1227multiple versions of perl.
1228
f105b7be 1229By setting C<-Duseversionedarchname>, the $archname will be
c2959982 1230distinct for architecture I<and> API version, allowing mixed use of
f105b7be 1231C<INSTALL_BASE>.
5ed58cbd
RS
1232
1233=item *
1234
ff772877
RS
1235Add a C<PERL_NO_INLINE_FUNCTIONS> option
1236
f105b7be 1237If C<PERL_NO_INLINE_FUNCTIONS> is defined, don't include "inline.h"
ff772877
RS
1238
1239This permits test code to include the perl headers for definitions without
1240creating a link dependency on the perl library (which may not exist yet).
1241
1242=item *
1243
5ed58cbd
RS
1244Configure will honour the external C<MAILDOMAIN> environment variable, if set.
1245
1246=item *
1247
1248C<installman> no longer ignores the silent option
1249
1250=item *
1251
1252Both C<META.yml> and C<META.json> files are now included in the distribution.
1253
1254=item *
1255
1256F<Configure> will now correctly detect C<isblank()> when compiling with a C++
1257compiler.
1258
1259=item *
1260
1261The pager detection in F<Configure> has been improved to allow responses which
1262specify options after the program name, e.g. B</usr/bin/less -R>, if the user
1263accepts the default value. This helps B<perldoc> when handling ANSI escapes
1264[perl #72156].
1265
1266=back
1267
1268=head1 Testing
1269
1270=over 4
1271
1272=item *
1273
1274The test suite now has a section for tests that require very large amounts
1275of memory. These tests won't run by default; they can be enabled by
1276setting the C<PERL_TEST_MEMORY> environment variable to the number of
1277gibibytes of memory that may be safely used.
1278
1279=back
1280
1281=head1 Platform Support
1282
1283=head2 Discontinued Platforms
1284
1285=over 4
1286
1287=item BeOS
1288
1289BeOS was an operating system for personal computers developed by Be Inc,
1290initially for their BeBox hardware. The OS Haiku was written as an open
1291source replacement for/continuation of BeOS, and its perl port is current and
1292actively maintained.
1293
1294=item UTS Global
1295
1296Support code relating to UTS global has been removed. UTS was a mainframe
1297version of System V created by Amdahl, subsequently sold to UTS Global. The
e612b5a0 1298port has not been touched since before Perl v5.8.0, and UTS Global is now
5ed58cbd
RS
1299defunct.
1300
1301=item VM/ESA
1302
1303Support for VM/ESA has been removed. The port was tested on 2.3.0, which
1304IBM ended service on in March 2002. 2.4.0 ended service in June 2003, and
1305was superseded by Z/VM. The current version of Z/VM is V6.2.0, and scheduled
1306for end of service on 2015/04/30.
1307
1308=item MPE/IX
1309
1310Support for MPE/IX has been removed.
1311
1312=item EPOC
1313
1314Support code relating to EPOC has been removed. EPOC was a family of
1315operating systems developed by Psion for mobile devices. It was the
1316predecessor of Symbian. The port was last updated in April 2002.
1317
1318=item Rhapsody
1319
1320Support for Rhapsody has been removed.
1321
1322=back
1323
1324=head2 Platform-Specific Notes
1325
1326=head3 AIX
1327
1328Configure now always adds C<-qlanglvl=extc99> to the CC flags on AIX when
1329using xlC. This will make it easier to compile a number of XS-based modules
1330that assume C99 [perl #113778].
1331
1332=head3 clang++
1333
1334There is now a workaround for a compiler bug that prevented compiling
e612b5a0 1335with clang++ since Perl v5.15.7 [perl #112786].
5ed58cbd
RS
1336
1337=head3 C++
1338
1339When compiling the Perl core as C++ (which is only semi-supported), the
1340mathom functions are now compiled as C<extern "C">, to ensure proper
1341binary compatibility. (However, binary compatibility isn't generally
1342guaranteed anyway in the situations where this would matter.)
1343
1344=head3 Darwin
1345
1346Stop hardcoding an alignment on 8 byte boundaries to fix builds using
1347-Dusemorebits.
1348
1349=head3 Haiku
1350
1351Perl should now work out of the box on Haiku R1 Alpha 4.
1352
1353=head3 MidnightBSD
1354
1355C<libc_r> was removed from recent versions of MidnightBSD and older versions
1356work better with C<pthread>. Threading is now enabled using C<pthread> which
1357corrects build errors with threading enabled on 0.4-CURRENT.
1358
1359=head3 Solaris
1360
1361In Configure, avoid running sed commands with flags not supported on Solaris.
1362
1363=head3 VMS
1364
1365=over
1366
1367=item *
1368
1369Where possible, the case of filenames and command-line arguments is now
1370preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
1371C<DECC$ARGV_PARSE_STYLE> at start-up time. The latter only takes effect
1372when extended parse is enabled in the process from which Perl is run.
1373
1374=item *
1375
1376The character set for Extended Filename Syntax (EFS) is now enabled by default
1377on VMS. Among other things, this provides better handling of dots in directory
05f5908f 1378names, multiple dots in filenames, and spaces in filenames. To obtain the old
5ed58cbd
RS
1379behavior, set the logical name C<DECC$EFS_CHARSET> to C<DISABLE>.
1380
1381=item *
1382
05f5908f 1383Fixed linking on builds configured with C<-Dusemymalloc=y>.
5ed58cbd
RS
1384
1385=item *
1386
05f5908f
CB
1387Experimental support for building Perl with the HP C++ compiler is available
1388by configuring with C<-Dusecxx>.
5ed58cbd
RS
1389
1390=item *
1391
1392All C header files from the top-level directory of the distribution are now
1393installed on VMS, providing consistency with a long-standing practice on other
1394platforms. Previously only a subset were installed, which broke non-core
1395extension builds for extensions that depended on the missing include files.
1396
1397=item *
1398
1399Quotes are now removed from the command verb (but not the parameters) for
1400commands spawned via C<system>, backticks, or a piped C<open>. Previously,
1401quotes on the verb were passed through to DCL, which would fail to recognize
1402the command. Also, if the verb is actually a path to an image or command
1403procedure on an ODS-5 volume, quoting it now allows the path to contain spaces.
1404
1405=item *
1406
1407The B<a2p> build has been fixed for the HP C++ compiler on OpenVMS.
1408
1409=back
1410
1411=head3 Win32
1412
1413=over
1414
1415=item *
1416
1417Perl can now be built using Microsoft's Visual C++ 2012 compiler by specifying
1418CCTYPE=MSVC110 (or MSVC110FREE if you are using the free Express edition for
1419Windows Desktop) in F<win32/Makefile>.
1420
1421=item *
1422
f105b7be 1423The option to build without C<USE_SOCKETS_AS_HANDLES> has been removed.
5ed58cbd
RS
1424
1425=item *
1426
1427Fixed a problem where perl could crash while cleaning up threads (including the
1428main thread) in threaded debugging builds on Win32 and possibly other platforms
1429[perl #114496].
1430
1431=item *
1432
1433A rare race condition that would lead to L<sleep|perlfunc/sleep> taking more
1434time than requested, and possibly even hanging, has been fixed [perl #33096].
1435
1436=item *
1437
1438C<link> on Win32 now attempts to set C<$!> to more appropriate values
1439based on the Win32 API error code. [perl #112272]
1440
1441Perl no longer mangles the environment block, e.g. when launching a new
1442sub-process, when the environment contains non-ASCII characters. Known
1443problems still remain, however, when the environment contains characters
1444outside of the current ANSI codepage (e.g. see the item about Unicode in
1445C<%ENV> in L<http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod>).
1446[perl #113536]
1447
1448=item *
1449
1450Building perl with some Windows compilers used to fail due to a problem
1451with miniperl's C<glob> operator (which uses the C<perlglob> program)
1452deleting the PATH environment variable [perl #113798].
1453
1454=item *
1455
f105b7be 1456A new makefile option, C<USE_64_BIT_INT>, has been added to the Windows
5ed58cbd
RS
1457makefiles. Set this to "define" when building a 32-bit perl if you want
1458it to use 64-bit integers.
1459
1460Machine code size reductions, already made to the DLLs of XS modules in
e612b5a0 1461Perl v5.17.2, have now been extended to the perl DLL itself.
5ed58cbd 1462
e612b5a0 1463Building with VC++ 6.0 was inadvertently broken in Perl v5.17.2 but has
5ed58cbd
RS
1464now been fixed again.
1465
1466=back
1467
1468=head3 WinCE
1469
1470Building on WinCE is now possible once again, although more work is required
1471to fully restore a clean build.
1472
1473=head1 Internal Changes
1474
1475=over
1476
1477=item *
1478
4263dd11 1479Synonyms for the misleadingly named C<av_len()> have been created:
5ed58cbd
RS
1480C<av_top_index()> and C<av_tindex>. All three of these return the
1481number of the highest index in the array, not the number of elements it
1482contains.
1483
1484=item *
1485
1486SvUPGRADE() is no longer an expression. Originally this macro (and its
1487underlying function, sv_upgrade()) were documented as boolean, although
1488in reality they always croaked on error and never returned false. In 2005
1489the documentation was updated to specify a void return value, but
1490SvUPGRADE() was left always returning 1 for backwards compatibility. This
1491has now been removed, and SvUPGRADE() is now a statement with no return
1492value.
1493
1494So this is now a syntax error:
1495
1496 if (!SvUPGRADE(sv)) { croak(...); }
1497
1498If you have code like that, simply replace it with
1499
1500 SvUPGRADE(sv);
1501
1502or to to avoid compiler warnings with older perls, possibly
1503
1504 (void)SvUPGRADE(sv);
1505
1506=item *
1507
1508Perl has a new copy-on-write mechanism that allows any SvPOK scalar to be
1509upgraded to a copy-on-write scalar. A reference count on the string buffer
d16360cf
RS
1510is stored in the string buffer itself. This feature is B<not enabled by
1511default>.
5ed58cbd 1512
d16360cf
RS
1513It can be enabled in a perl build by running F<Configure> with
1514B<-Accflags=-DPERL_NEW_COPY_ON_WRITE>, and we would encourage XS authors
1515to try their code with such an enabled perl, and provide feedback.
1516Unfortunately, there is not yet a good guide to updating XS code to cope
1517with COW. Until such a document is available, consult the perl5-porters
1518mailing list.
5ed58cbd 1519
d16360cf
RS
1520It breaks a few XS modules by allowing copy-on-write scalars to go
1521through code paths that never encountered them before.
5ed58cbd
RS
1522
1523=item *
1524
1525Copy-on-write no longer uses the SvFAKE and SvREADONLY flags. Hence,
1526SvREADONLY indicates a true read-only SV.
1527
1528Use the SvIsCOW macro (as before) to identify a copy-on-write scalar.
1529
1530=item *
1531
f105b7be 1532C<PL_glob_index> is gone.
5ed58cbd
RS
1533
1534=item *
1535
1536The private Perl_croak_no_modify has had its context parameter removed. It is
1537now has a void prototype. Users of the public API croak_no_modify remain
1538unaffected.
1539
1540=item *
1541
1542Copy-on-write (shared hash key) scalars are no longer marked read-only.
1543C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
1544true.
1545
1546=item *
1547
1548A new op type, C<OP_PADRANGE> has been introduced. The perl peephole
1549optimiser will, where possible, substitute a single padrange op for a
1550pushmark followed by one or more pad ops, and possibly also skipping list
1551and nextstate ops. In addition, the op can carry out the tasks associated
f105b7be 1552with the RHS of a C<< my(...) = @_ >> assignment, so those ops may be optimised
5ed58cbd
RS
1553away too.
1554
1555=item *
1556
1557Case-insensitive matching inside a [bracketed] character class with a
1558multi-character fold no longer excludes one of the possibilities in the
1559circumstances that it used to. [perl #89774].
1560
1561=item *
1562
1563C<PL_formfeed> has been removed.
1564
1565=item *
1566
1567The regular expression engine no longer reads one byte past the end of the
1568target string. While for all internally well-formed scalars this should
1569never have been a problem, this change facilitates clever tricks with
1570string buffers in CPAN modules. [perl #73542]
1571
1572=item *
1573
1574Inside a BEGIN block, C<PL_compcv> now points to the currently-compiling
1575subroutine, rather than the BEGIN block itself.
1576
1577=item *
1578
1579C<mg_length> has been deprecated.
1580
1581=item *
1582
1583C<sv_len> now always returns a byte count and C<sv_len_utf8> a character
1584count. Previously, C<sv_len> and C<sv_len_utf8> were both buggy and would
1585sometimes returns bytes and sometimes characters. C<sv_len_utf8> no longer
be12dd22 1586assumes that its argument is in UTF-8. Neither of these creates UTF-8 caches
5ed58cbd
RS
1587for tied or overloaded values or for non-PVs any more.
1588
1589=item *
1590
1591C<sv_mortalcopy> now copies string buffers of shared hash key scalars when
1592called from XS modules [perl #79824].
1593
1594=item *
1595
1596C<RXf_SPLIT> and C<RXf_SKIPWHITE> are no longer used. They are now
1597#defined as 0.
1598
1599=item *
1600
1601The new C<RXf_MODIFIES_VARS> flag can be set by custom regular expression
1602engines to indicate that the execution of the regular expression may cause
1603variables to be modified. This lets C<s///> know to skip certain
1604optimisations. Perl's own regular expression engine sets this flag for the
1605special backtracking verbs that set $REGMARK and $REGERROR.
1606
1607=item *
1608
1609The APIs for accessing lexical pads have changed considerably.
1610
1611C<PADLIST>s are now longer C<AV>s, but their own type instead.
1612C<PADLIST>s now contain a C<PAD> and a C<PADNAMELIST> of C<PADNAME>s,
1613rather than C<AV>s for the pad and the list of pad names. C<PAD>s,
1614C<PADNAMELIST>s, and C<PADNAME>s are to be accessed as such through the
1615newly added pad API instead of the plain C<AV> and C<SV> APIs. See
1616L<perlapi> for details.
1617
1618=item *
1619
1620In the regex API, the numbered capture callbacks are passed an index
1621indicating what match variable is being accessed. There are special
1622index values for the C<$`, $&, $&> variables. Previously the same three
1623values were used to retrieve C<${^PREMATCH}, ${^MATCH}, ${^POSTMATCH}>
1624too, but these have now been assigned three separate values. See
1625L<perlreapi/Numbered capture callbacks>.
1626
1627=item *
1628
1629C<PL_sawampersand> was previously a boolean indicating that any of
1630C<$`, $&, $&> had been seen; it now contains three one-bit flags
1631indicating the presence of each of the variables individually.
1632
1633=item *
1634
1635The C<CV *> typemap entry now supports C<&{}> overloading and typeglobs,
1636just like C<&{...}> [perl #96872].
1637
1638=item *
1639
1640The C<SVf_AMAGIC> flag to indicate overloading is now on the stash, not the
1641object. It is now set automatically whenever a method or @ISA changes, so
1642its meaning has changed, too. It now means "potentially overloaded". When
1643the overload table is calculated, the flag is automatically turned off if
1644there is no overloading, so there should be no noticeable slowdown.
1645
1646The staleness of the overload tables is now checked when overload methods
1647are invoked, rather than during C<bless>.
1648
1649"A" magic is gone. The changes to the handling of the C<SVf_AMAGIC> flag
1650eliminate the need for it.
1651
1652C<PL_amagic_generation> has been removed as no longer necessary. For XS
1653modules, it is now a macro alias to C<PL_na>.
1654
1655The fallback overload setting is now stored in a stash entry separate from
1656overloadedness itself.
1657
1658=item *
1659
1660The character-processing code has been cleaned up in places. The changes
1661should be operationally invisible.
1662
1663=item *
1664
e612b5a0 1665The C<study> function was made a no-op in v5.16. It was simply disabled via
5ed58cbd
RS
1666a C<return> statement; the code was left in place. Now the code supporting
1667what C<study> used to do has been removed.
1668
1669=item *
1670
1671Under threaded perls, there is no longer a separate PV allocated for every
1672COP to store its package name (C<< cop->stashpv >>). Instead, there is an
1673offset (C<< cop->stashoff >>) into the new C<PL_stashpad> array, which
1674holds stash pointers.
1675
1676=item *
1677
1678In the pluggable regex API, the C<regexp_engine> struct has acquired a new
1679field C<op_comp>, which is currently just for perl's internal use, and
f105b7be 1680should be initialized to NULL by other regex plugin modules.
5ed58cbd
RS
1681
1682=item *
1683
7779650e 1684A new function C<alloccopstash> has been added to the API, but is considered
5ed58cbd
RS
1685experimental. See L<perlapi>.
1686
1687=item *
1688
1689Perl used to implement get magic in a way that would sometimes hide bugs in
4263dd11 1690code that could call mg_get() too many times on magical values. This hiding of
5ed58cbd
RS
1691errors no longer occurs, so long-standing bugs may become visible now. If
1692you see magic-related errors in XS code, check to make sure it, together
1693with the Perl API functions it uses, calls mg_get() only once on SvGMAGICAL()
1694values.
1695
1696=item *
1697
1698OP allocation for CVs now uses a slab allocator. This simplifies
1699memory management for OPs allocated to a CV, so cleaning up after a
1700compilation error is simpler and safer [perl #111462][perl #112312].
1701
1702=item *
1703
f105b7be 1704C<PERL_DEBUG_READONLY_OPS> has been rewritten to work with the new slab
5ed58cbd
RS
1705allocator, allowing it to catch more violations than before.
1706
1707=item *
1708
f105b7be
KE
1709The old slab allocator for ops, which was only enabled for C<PERL_IMPLICIT_SYS>
1710and C<PERL_DEBUG_READONLY_OPS>, has been retired.
5ed58cbd
RS
1711
1712=back
1713
1714=head1 Selected Bug Fixes
1715
1716=over 4
1717
1718=item *
1719
1720Here-doc terminators no longer require a terminating newline character when
1721they occur at the end of a file. This was already the case at the end of a
1722string eval [perl #65838].
1723
1724=item *
1725
f105b7be 1726C<-DPERL_GLOBAL_STRUCT> builds now free the global struct B<after>
5ed58cbd
RS
1727they've finished using it.
1728
1729=item *
1730
1731A trailing '/' on a path in @INC will no longer have an additional '/'
1732appended.
1733
1734=item *
1735
1736The C<:crlf> layer now works when unread data doesn't fit into its own
1737buffer. [perl #112244].
1738
1739=item *
1740
1741C<ungetc()> now handles UTF-8 encoded data. [perl #116322].
1742
1743=item *
1744
1745A bug in the core typemap caused any C types that map to the T_BOOL core
1746typemap entry to not be set, updated, or modified when the T_BOOL variable was
1747used in an OUTPUT: section with an exception for RETVAL. T_BOOL in an INPUT:
1748section was not affected. Using a T_BOOL return type for an XSUB (RETVAL)
1749was not affected. A side effect of fixing this bug is, if a T_BOOL is specified
1750in the OUTPUT: section (which previous did nothing to the SV), and a read only
1751SV (literal) is passed to the XSUB, croaks like "Modification of a read-only
1752value attempted" will happen. [perl #115796]
1753
1754=item *
1755
1756On many platforms, providing a directory name as the script name caused perl
1757to do nothing and report success. It should now universally report an error
1758and exit nonzero. [perl #61362]
1759
1760=item *
1761
1762C<sort {undef} ...> under fatal warnings no longer crashes. It had
e612b5a0 1763begun crashing in Perl v5.16.
5ed58cbd
RS
1764
1765=item *
1766
1767Stashes blessed into each other
1768(C<bless \%Foo::, 'Bar'; bless \%Bar::, 'Foo'>) no longer result in double
e612b5a0 1769frees. This bug started happening in Perl v5.16.
5ed58cbd
RS
1770
1771=item *
1772
1773Numerous memory leaks have been fixed, mostly involving fatal warnings and
1774syntax errors.
1775
1776=item *
1777
1778Some failed regular expression matches such as C<'f' =~ /../g> were not
1779resetting C<pos>. Also, "match-once" patterns (C<m?...?g>) failed to reset
1780it, too, when invoked a second time [perl #23180].
1781
1782=item *
1783
1784Accessing C<$&> after a pattern match now works if it had not been seen
1785before the match. I.e., this applies to C<${'&'}> (under C<no strict>) and
1786C<eval '$&'>. The same applies to C<$'> and C<$`> [perl #4289].
1787
1788=item *
1789
1790Several bugs involving C<local *ISA> and C<local *Foo::> causing stale
1791MRO caches have been fixed.
1792
1793=item *
1794
1795Defining a subroutine when its typeglob has been aliased no longer results
e612b5a0 1796in stale method caches. This bug was introduced in Perl v5.10.
5ed58cbd
RS
1797
1798=item *
1799
1800Localising a typeglob containing a subroutine when the typeglob's package
1801has been deleted from its parent stash no longer produces an error. This
e612b5a0 1802bug was introduced in Perl v5.14.
5ed58cbd
RS
1803
1804=item *
1805
1806Under some circumstances, C<local *method=...> would fail to reset method
1807caches upon scope exit.
1808
1809=item *
1810
1811C</[.foo.]/> is no longer an error, but produces a warning (as before) and
1812is treated as C</[.fo]/> [perl #115818].
1813
1814=item *
1815
1816C<goto $tied_var> now calls FETCH before deciding what type of goto
1817(subroutine or label) this is.
1818
1819=item *
1820
1821Renaming packages through glob assignment
1822(C<*Foo:: = *Bar::; *Bar:: = *Baz::>) in combination with C<m?...?> and
1823C<reset> no longer makes threaded builds crash.
1824
1825=item *
1826
1827A number of bugs related to assigning a list to hash have been fixed. Many of
1828these involve lists with repeated keys like C<(1, 1, 1, 1)>.
1829
1830=over 4
1831
1832=item *
1833
1834The expression C<scalar(%h = (1, 1, 1, 1))> now returns C<4>, not C<2>.
1835
1836=item *
1837
1838The return value of C<%h = (1, 1, 1)> in list context was wrong. Previously
1839this would return C<(1, undef, 1)>, now it returns C<(1, undef)>.
1840
1841=item *
1842
1843Perl now issues the same warning on C<($s, %h) = (1, {})> as it does for
1844C<(%h) = ({})>, "Reference found where even-sized list expected".
1845
1846=item *
1847
1848A number of additional edge cases in list assignment to hashes were
1849corrected. For more details see commit 23b7025ebc.
1850
1851=back
1852
1853=item *
1854
1855Attributes applied to lexical variables no longer leak memory.
1856[perl #114764]
1857
1858=item *
1859
1860C<dump>, C<goto>, C<last>, C<next>, C<redo> or C<require> followed by a
1861bareword (or version) and then an infix operator is no longer a syntax
1862error. It used to be for those infix operators (like C<+>) that have a
1863different meaning where a term is expected. [perl #105924]
1864
1865=item *
1866
1867C<require a::b . 1> and C<require a::b + 1> no longer produce erroneous
1868ambiguity warnings. [perl #107002]
1869
1870=item *
1871
1872Class method calls are now allowed on any string, and not just strings
1873beginning with an alphanumeric character. [perl #105922]
1874
1875=item *
1876
1877An empty pattern created with C<qr//> used in C<m///> no longer triggers
1878the "empty pattern reuses last pattern" behaviour. [perl #96230]
1879
1880=item *
1881
1882Tying a hash during iteration no longer results in a memory leak.
1883
1884=item *
1885
1886Freeing a tied hash during iteration no longer results in a memory leak.
1887
1888=item *
1889
1890List assignment to a tied array or hash that dies on STORE no longer
1891results in a memory leak.
1892
1893=item *
1894
1895If the hint hash (C<%^H>) is tied, compile-time scope entry (which copies
1896the hint hash) no longer leaks memory if FETCH dies. [perl #107000]
1897
1898=item *
1899
1900Constant folding no longer inappropriately triggers the special
1901C<split " "> behaviour. [perl #94490]
1902
1903=item *
1904
1905C<defined scalar(@array)>, C<defined do { &foo }>, and similar constructs
1906now treat the argument to C<defined> as a simple scalar. [perl #97466]
1907
1908=item *
1909
1910Running a custom debugging that defines no C<*DB::DB> glob or provides a
1911subroutine stub for C<&DB::DB> no longer results in a crash, but an error
1912instead. [perl #114990]
1913
1914=item *
1915
1916C<reset ""> now matches its documentation. C<reset> only resets C<m?...?>
1917patterns when called with no argument. An empty string for an argument now
1918does nothing. (It used to be treated as no argument.) [perl #97958]
1919
1920=item *
1921
1922C<printf> with an argument returning an empty list no longer reads past the
1923end of the stack, resulting in erratic behaviour. [perl #77094]
1924
1925=item *
1926
1927C<--subname> no longer produces erroneous ambiguity warnings.
1928[perl #77240]
1929
1930=item *
1931
1932C<v10> is now allowed as a label or package name. This was inadvertently
e612b5a0 1933broken when v-strings were added in Perl v5.6. [perl #56880]
5ed58cbd
RS
1934
1935=item *
1936
1937C<length>, C<pos>, C<substr> and C<sprintf> could be confused by ties,
1938overloading, references and typeglobs if the stringification of such
be12dd22 1939changed the internal representation to or from UTF-8. [perl #114410]
5ed58cbd
RS
1940
1941=item *
1942
1943utf8::encode now calls FETCH and STORE on tied variables. utf8::decode now
1944calls STORE (it was already calling FETCH).
1945
1946=item *
1947
1948C<$tied =~ s/$non_utf8/$utf8/> no longer loops infinitely if the tied
1949variable returns a Latin-1 string, shared hash key scalar, or reference or
2ae351f8 1950typeglob that stringifies as ASCII or Latin-1. This was a regression from
e612b5a0 1951v5.12.
5ed58cbd
RS
1952
1953=item *
1954
1955C<s///> without /e is now better at detecting when it needs to forego
1956certain optimisations, fixing some buggy cases:
1957
1958=over
1959
1960=item *
1961
1962Match variables in certain constructs (C<&&>, C<||>, C<..> and others) in
1963the replacement part; e.g., C<s/(.)/$l{$a||$1}/g>. [perl #26986]
1964
1965=item *
1966
1967Aliases to match variables in the replacement.
1968
1969=item *
1970
1971C<$REGERROR> or C<$REGMARK> in the replacement. [perl #49190]
1972
1973=item *
1974
1975An empty pattern (C<s//$foo/>) that causes the last-successful pattern to
1976be used, when that pattern contains code blocks that modify the variables
1977in the replacement.
1978
1979=back
1980
1981=item *
1982
1983The taintedness of the replacement string no longer affects the taintedness
1984of the return value of C<s///e>.
1985
1986=item *
1987
1988The C<$|> autoflush variable is created on-the-fly when needed. If this
1989happened (e.g., if it was mentioned in a module or eval) when the
1990currently-selected filehandle was a typeglob with an empty IO slot, it used
1991to crash. [perl #115206]
1992
1993=item *
1994
1995Line numbers at the end of a string eval are no longer off by one.
1996[perl #114658]
1997
1998=item *
1999
2000@INC filters (subroutines returned by subroutines in @INC) that set $_ to a
2001copy-on-write scalar no longer cause the parser to modify that string
2002buffer in place.
2003
2004=item *
2005
2006C<length($object)> no longer returns the undefined value if the object has
2007string overloading that returns undef. [perl #115260]
2008
2009=item *
2010
2011The use of C<PL_stashcache>, the stash name lookup cache for method calls, has
2012been restored,
2013
2014Commit da6b625f78f5f133 in August 2011 inadvertently broke the code that looks
2015up values in C<PL_stashcache>. As it's a only cache, quite correctly everything
2016carried on working without it.
2017
2018=item *
2019
e612b5a0 2020The error "Can't localize through a reference" had disappeared in v5.16.0
5ed58cbd 2021when C<local %$ref> appeared on the last line of an lvalue subroutine.
e612b5a0 2022This error disappeared for C<\local %$ref> in perl v5.8.1. It has now
5ed58cbd
RS
2023been restored.
2024
2025=item *
2026
2027The parsing of here-docs has been improved significantly, fixing several
2028parsing bugs and crashes and one memory leak, and correcting wrong
2029subsequent line numbers under certain conditions.
2030
2031=item *
2032
2033Inside an eval, the error message for an unterminated here-doc no longer
2034has a newline in the middle of it [perl #70836].
2035
2036=item *
2037
2038A substitution inside a substitution pattern (C<s/${s|||}//>) no longer
2039confuses the parser.
2040
2041=item *
2042
2043It may be an odd place to allow comments, but C<s//"" # hello/e> has
2044always worked, I<unless> there happens to be a null character before the
2045first #. Now it works even in the presence of nulls.
2046
2047=item *
2048
2049An invalid range in C<tr///> or C<y///> no longer results in a memory leak.
2050
2051=item *
2052
2053String eval no longer treats a semicolon-delimited quote-like operator at
2054the very end (C<eval 'q;;'>) as a syntax error.
2055
2056=item *
2057
2058C<< warn {$_ => 1} + 1 >> is no longer a syntax error. The parser used to
2059get confused with certain list operators followed by an anonymous hash and
2060then an infix operator that shares its form with a unary operator.
2061
2062=item *
2063
2064C<(caller $n)[6]> (which gives the text of the eval) used to return the
2065actual parser buffer. Modifying it could result in crashes. Now it always
2066returns a copy. The string returned no longer has "\n;" tacked on to the
2067end. The returned text also includes here-doc bodies, which used to be
2068omitted.
2069
2070=item *
2071
be12dd22
RS
2072Reset the UTF-8 position cache when accessing magical variables to avoid the
2073string buffer and the UTF-8 position cache getting out of sync
5ed58cbd
RS
2074[perl #114410].
2075
2076=item *
2077
be12dd22
RS
2078Various cases of get magic being called twice for magical UTF-8
2079strings have been fixed.
5ed58cbd
RS
2080
2081=item *
2082
2083This code (when not in the presence of C<$&> etc)
2084
2085 $_ = 'x' x 1_000_000;
2086 1 while /(.)/;
2087
2088used to skip the buffer copy for performance reasons, but suffered from C<$1>
2089etc changing if the original string changed. That's now been fixed.
2090
2091=item *
2092
2093Perl doesn't use PerlIO anymore to report out of memory messages, as PerlIO
2094might attempt to allocate more memory.
2095
2096=item *
2097
2098In a regular expression, if something is quantified with C<{n,m}> where
2099C<S<n E<gt> m>>, it can't possibly match. Previously this was a fatal
2100error, but now is merely a warning (and that something won't match).
2101[perl #82954].
2102
2103=item *
2104
2105It used to be possible for formats defined in subroutines that have
2106subsequently been undefined and redefined to close over variables in the
2107wrong pad (the newly-defined enclosing sub), resulting in crashes or
2108"Bizarre copy" errors.
2109
2110=item *
2111
2112Redefinition of XSUBs at run time could produce warnings with the wrong
2113line number.
2114
2115=item *
2116
2117The %vd sprintf format does not support version objects for alpha versions.
2118It used to output the format itself (%vd) when passed an alpha version, and
2119also emit an "Invalid conversion in printf" warning. It no longer does,
2120but produces the empty string in the output. It also no longer leaks
2121memory in this case.
2122
2123=item *
2124
2125C<< $obj->SUPER::method >> calls in the main package could fail if the
2126SUPER package had already been accessed by other means.
2127
2128=item *
2129
f105b7be 2130Stash aliasing (C<< *foo:: = *bar:: >>) no longer causes SUPER calls to ignore
5ed58cbd
RS
2131changes to methods or @ISA or use the wrong package.
2132
2133=item *
2134
2135Method calls on packages whose names end in ::SUPER are no longer treated
2136as SUPER method calls, resulting in failure to find the method.
2137Furthermore, defining subroutines in such packages no longer causes them to
2138be found by SUPER method calls on the containing package [perl #114924].
2139
2140=item *
2141
2142C<\w> now matches the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D
2143(ZERO WIDTH JOINER). C<\W> no longer matches these. This change is because
2144Unicode corrected their definition of what C<\w> should match.
2145
2146=item *
2147
2148C<dump LABEL> no longer leaks its label.
2149
2150=item *
2151
2152Constant folding no longer changes the behaviour of functions like C<stat()>
2153and C<truncate()> that can take either filenames or handles.
2154C<stat 1 ? foo : bar> nows treats its argument as a file name (since it is an
2155arbitrary expression), rather than the handle "foo".
2156
2157=item *
2158
2159C<truncate FOO, $len> no longer falls back to treating "FOO" as a file name if
e612b5a0 2160the filehandle has been deleted. This was broken in Perl v5.16.0.
5ed58cbd
RS
2161
2162=item *
2163
2164Subroutine redefinitions after sub-to-glob and glob-to-glob assignments no
2165longer cause double frees or panic messages.
2166
2167=item *
2168
2169C<s///> now turns vstrings into plain strings when performing a substitution,
2170even if the resulting string is the same (C<s/a/a/>).
2171
2172=item *
2173
2174Prototype mismatch warnings no longer erroneously treat constant subs as having
2175no prototype when they actually have "".
2176
2177=item *
2178
2179Constant subroutines and forward declarations no longer prevent prototype
2180mismatch warnings from omitting the sub name.
2181
2182=item *
2183
2184C<undef> on a subroutine now clears call checkers.
2185
2186=item *
2187
e612b5a0 2188The C<ref> operator started leaking memory on blessed objects in Perl v5.16.0.
5ed58cbd
RS
2189This has been fixed [perl #114340].
2190
2191=item *
2192
2193C<use> no longer tries to parse its arguments as a statement, making
2194C<use constant { () };> a syntax error [perl #114222].
2195
2196=item *
2197
2198On debugging builds, "uninitialized" warnings inside formats no longer cause
2199assertion failures.
2200
2201=item *
2202
2203On debugging builds, subroutines nested inside formats no longer cause
2204assertion failures [perl #78550].
2205
2206=item *
2207
2208Formats and C<use> statements are now permitted inside formats.
2209
2210=item *
2211
2212C<print $x> and C<sub { print $x }-E<gt>()> now always produce the same output.
2213It was possible for the latter to refuse to close over $x if the variable was
2214not active; e.g., if it was defined outside a currently-running named
2215subroutine.
2216
2217=item *
2218
2219Similarly, C<print $x> and C<print eval '$x'> now produce the same output.
2220This also allows "my $x if 0" variables to be seen in the debugger [perl
2221#114018].
2222
2223=item *
2224
2225Formats called recursively no longer stomp on their own lexical variables, but
2226each recursive call has its own set of lexicals.
2227
2228=item *
2229
2230Attempting to free an active format or the handle associated with it no longer
2231results in a crash.
2232
2233=item *
2234
2235Format parsing no longer gets confused by braces, semicolons and low-precedence
2236operators. It used to be possible to use braces as format delimiters (instead
2237of C<=> and C<.>), but only sometimes. Semicolons and low-precedence operators
2238in format argument lines no longer confuse the parser into ignoring the line's
2239return value. In format argument lines, braces can now be used for anonymous
2240hashes, instead of being treated always as C<do> blocks.
2241
2242=item *
2243
2244Formats can now be nested inside code blocks in regular expressions and other
2245quoted constructs (C</(?{...})/> and C<qq/${...}/>) [perl #114040].
2246
2247=item *
2248
2249Formats are no longer created after compilation errors.
2250
2251=item *
2252
2253Under debugging builds, the B<-DA> command line option started crashing in Perl
e612b5a0 2254v5.16.0. It has been fixed [perl #114368].
5ed58cbd
RS
2255
2256=item *
2257
2258A potential deadlock scenario involving the premature termination of a pseudo-
2259forked child in a Windows build with ithreads enabled has been fixed. This
2260resolves the common problem of the F<t/op/fork.t> test hanging on Windows [perl
2261#88840].
2262
2263=item *
2264
5ed58cbd
RS
2265The code which generates errors from C<require()> could potentially read one or
2266two bytes before the start of the filename for filenames less than three bytes
2267long and ending C</\.p?\z/>. This has now been fixed. Note that it could
2268never have happened with module names given to C<use()> or C<require()> anyway.
2269
2270=item *
2271
2272The handling of pathnames of modules given to C<require()> has been made
2273thread-safe on VMS.
2274
2275=item *
2276
d85cd26b
RS
2277Non-blocking sockets have been fixed on VMS.
2278
2279=item *
2280
5ed58cbd
RS
2281A bug in the compilation of a C</(?{})/> expression which affected the TryCatch
2282test suite has been fixed [perl #114242].
2283
2284=item *
2285
2286Pod can now be nested in code inside a quoted construct outside of a string
2287eval. This used to work only within string evals [perl #114040].
2288
2289=item *
2290
2291C<goto ''> now looks for an empty label, producing the "goto must have
2292label" error message, instead of exiting the program [perl #111794].
2293
2294=item *
2295
2296C<goto "\0"> now dies with "Can't find label" instead of "goto must have
2297label".
2298
2299=item *
2300
2301The C function C<hv_store> used to result in crashes when used on C<%^H>
2302[perl #111000].
2303
2304=item *
2305
2306A call checker attached to a closure prototype via C<cv_set_call_checker>
2307is now copied to closures cloned from it. So C<cv_set_call_checker> now
2308works inside an attribute handler for a closure.
2309
2310=item *
2311
2312Writing to C<$^N> used to have no effect. Now it croaks with "Modification
2313of a read-only value" by default, but that can be overridden by a custom
2314regular expression engine, as with C<$1> [perl #112184].
2315
2316=item *
2317
2318C<undef> on a control character glob (C<undef *^H>) no longer emits an
2319erroneous warning about ambiguity [perl #112456].
2320
2321=item *
2322
2323For efficiency's sake, many operators and built-in functions return the
2324same scalar each time. Lvalue subroutines and subroutines in the CORE::
2325namespace were allowing this implementation detail to leak through.
2326C<print &CORE::uc("a"), &CORE::uc("b")> used to print "BB". The same thing
2327would happen with an lvalue subroutine returning the return value of C<uc>.
2328Now the value is copied in such cases.
2329
2330=item *
2331
2332C<method {}> syntax with an empty block or a block returning an empty list
2333used to crash or use some random value left on the stack as its invocant.
2334Now it produces an error.
2335
2336=item *
2337
2338C<vec> now works with extremely large offsets (E<gt>2 GB) [perl #111730].
2339
2340=item *
2341
2342Changes to overload settings now take effect immediately, as do changes to
2343inheritance that affect overloading. They used to take effect only after
2344C<bless>.
2345
2346Objects that were created before a class had any overloading used to remain
2347non-overloaded even if the class gained overloading through C<use overload>
2348or @ISA changes, and even after C<bless>. This has been fixed
2349[perl #112708].
2350
2351=item *
2352
2353Classes with overloading can now inherit fallback values.
2354
2355=item *
2356
2357Overloading was not respecting a fallback value of 0 if there were
2358overloaded objects on both sides of an assignment operator like C<+=>
2359[perl #111856].
2360
2361=item *
2362
2363C<pos> now croaks with hash and array arguments, instead of producing
2364erroneous warnings.
2365
2366=item *
2367
2368C<while(each %h)> now implies C<while(defined($_ = each %h))>, like
2369C<readline> and C<readdir>.
2370
2371=item *
2372
2373Subs in the CORE:: namespace no longer crash after C<undef *_> when called
2374with no argument list (C<&CORE::time> with no parentheses).
2375
2376=item *
2377
2378C<unpack> no longer produces the "'/' must follow a numeric type in unpack"
2379error when it is the data that are at fault [perl #60204].
2380
2381=item *
2382
2383C<join> and C<"@array"> now call FETCH only once on a tied C<$">
2384[perl #8931].
2385
2386=item *
2387
2388Some subroutine calls generated by compiling core ops affected by a
2389C<CORE::GLOBAL> override had op checking performed twice. The checking
2390is always idempotent for pure Perl code, but the double checking can
2391matter when custom call checkers are involved.
2392
2393=item *
2394
2395A race condition used to exist around fork that could cause a signal sent to
2396the parent to be handled by both parent and child. Signals are now blocked
2397briefly around fork to prevent this from happening [perl #82580].
2398
2399=item *
2400
2401The implementation of code blocks in regular expressions, such as C<(?{})>
2402and C<(??{})>, has been heavily reworked to eliminate a whole slew of bugs.
2403The main user-visible changes are:
2404
2405=over 4
2406
2407=item *
2408
2409Code blocks within patterns are now parsed in the same pass as the
2410surrounding code; in particular it is no longer necessary to have balanced
2411braces: this now works:
2412
2413 /(?{ $x='{' })/
2414
2415This means that this error message is no longer generated:
2416
2417 Sequence (?{...}) not terminated or not {}-balanced in regex
2418
2419but a new error may be seen:
2420
2421 Sequence (?{...}) not terminated with ')'
2422
2423In addition, literal code blocks within run-time patterns are only
2424compiled once, at perl compile-time:
2425
2426 for my $p (...) {
2427 # this 'FOO' block of code is compiled once,
2428 # at the same time as the surrounding 'for' loop
2429 /$p{(?{FOO;})/;
2430 }
2431
2432=item *
2433
2434Lexical variables are now sane as regards scope, recursion and closure
2435behavior. In particular, C</A(?{B})C/> behaves (from a closure viewpoint)
2436exactly like C</A/ && do { B } && /C/>, while C<qr/A(?{B})C/> is like
2437C<sub {/A/ && do { B } && /C/}>. So this code now works how you might
2438expect, creating three regexes that match 0, 1, and 2:
2439
2440 for my $i (0..2) {
2441 push @r, qr/^(??{$i})$/;
2442 }
2443 "1" =~ $r[1]; # matches
2444
2445=item *
2446
2447The C<use re 'eval'> pragma is now only required for code blocks defined
2448at runtime; in particular in the following, the text of the C<$r> pattern is
2449still interpolated into the new pattern and recompiled, but the individual
2450compiled code-blocks within C<$r> are reused rather than being recompiled,
2451and C<use re 'eval'> isn't needed any more:
2452
2453 my $r = qr/abc(?{....})def/;
2454 /xyz$r/;
2455
2456=item *
2457
2458Flow control operators no longer crash. Each code block runs in a new
2459dynamic scope, so C<next> etc. will not see
2460any enclosing loops. C<return> returns a value
2461from the code block, not from any enclosing subroutine.
2462
2463=item *
2464
2465Perl normally caches the compilation of run-time patterns, and doesn't
2466recompile if the pattern hasn't changed, but this is now disabled if
2467required for the correct behavior of closures. For example:
2468
2469 my $code = '(??{$x})';
2470 for my $x (1..3) {
2471 # recompile to see fresh value of $x each time
2472 $x =~ /$code/;
2473 }
2474
2475=item *
2476
2477The C</msix> and C<(?msix)> etc. flags are now propagated into the return
2478value from C<(??{})>; this now works:
2479
2480 "AB" =~ /a(??{'b'})/i;
2481
2482=item *
2483
2484Warnings and errors will appear to come from the surrounding code (or for
2485run-time code blocks, from an eval) rather than from an C<re_eval>:
2486
2487 use re 'eval'; $c = '(?{ warn "foo" })'; /$c/;
2488 /(?{ warn "foo" })/;
2489
2490formerly gave:
2491
2492 foo at (re_eval 1) line 1.
2493 foo at (re_eval 2) line 1.
2494
2495and now gives:
2496
2497 foo at (eval 1) line 1.
2498 foo at /some/prog line 2.
2499
2500=back
2501
2502=item *
2503
2e7bc647
KW
2504Perl now can be recompiled to use any Unicode version. In v5.16, it
2505worked on Unicodes 6.0 and 6.1, but there were various bugs if earlier
2506releases were used; the older the release the more problems.
5ed58cbd
RS
2507
2508=item *
2509
2510C<vec> no longer produces "uninitialized" warnings in lvalue context
2511[perl #9423].
2512
2513=item *
2514
2515An optimization involving fixed strings in regular expressions could cause
2516a severe performance penalty in edge cases. This has been fixed
2517[perl #76546].
2518
2519=item *
2520
2521In certain cases, including empty subpatterns within a regular expression (such
2522as C<(?:)> or C<(?:|)>) could disable some optimizations. This has been fixed.
2523
2524=item *
2525
2526The "Can't find an opnumber" message that C<prototype> produces when passed
2527a string like "CORE::nonexistent_keyword" now passes UTF-8 and embedded
2528NULs through unchanged [perl #97478].
2529
2530=item *
2531
2532C<prototype> now treats magical variables like C<$1> the same way as
2533non-magical variables when checking for the CORE:: prefix, instead of
2534treating them as subroutine names.
2535
2536=item *
2537
2538Under threaded perls, a runtime code block in a regular expression could
2539corrupt the package name stored in the op tree, resulting in bad reads
2540in C<caller>, and possibly crashes [perl #113060].
2541
2542=item *
2543
2544Referencing a closure prototype (C<\&{$_[1]}> in an attribute handler for a
2545closure) no longer results in a copy of the subroutine (or assertion
2546failures on debugging builds).
2547
2548=item *
2549
2550C<eval '__PACKAGE__'> now returns the right answer on threaded builds if
2551the current package has been assigned over (as in
2552C<*ThisPackage:: = *ThatPackage::>) [perl #78742].
2553
2554=item *
2555
2556If a package is deleted by code that it calls, it is possible for C<caller>
2557to see a stack frame belonging to that deleted package. C<caller> could
2558crash if the stash's memory address was reused for a scalar and a
2559substitution was performed on the same scalar [perl #113486].
2560
2561=item *
2562
2563C<UNIVERSAL::can> no longer treats its first argument differently
2564depending on whether it is a string or number internally.
2565
2566=item *
2567
2568C<open> with C<< <& >> for the mode checks to see whether the third argument is
2569a number, in determining whether to treat it as a file descriptor or a handle
2570name. Magical variables like C<$1> were always failing the numeric check and
2571being treated as handle names.
2572
2573=item *
2574
2575C<warn>'s handling of magical variables (C<$1>, ties) has undergone several
2576fixes. C<FETCH> is only called once now on a tied argument or a tied C<$@>
2577[perl #97480]. Tied variables returning objects that stringify as "" are
2578no longer ignored. A tied C<$@> that happened to return a reference the
2579I<previous> time it was used is no longer ignored.
2580
2581=item *
2582
2583C<warn ""> now treats C<$@> with a number in it the same way, regardless of
2584whether it happened via C<$@=3> or C<$@="3">. It used to ignore the
2585former. Now it appends "\t...caught", as it has always done with
2586C<$@="3">.
2587
2588=item *
2589
2590Numeric operators on magical variables (e.g., S<C<$1 + 1>>) used to use
2591floating point operations even where integer operations were more appropriate,
2592resulting in loss of accuracy on 64-bit platforms [perl #109542].
2593
2594=item *
2595
2596Unary negation no longer treats a string as a number if the string happened
2597to be used as a number at some point. So, if C<$x> contains the string "dogs",
2598C<-$x> returns "-dogs" even if C<$y=0+$x> has happened at some point.
2599
2600=item *
2601
e612b5a0 2602In Perl v5.14, C<-'-10'> was fixed to return "10", not "+10". But magical
5ed58cbd
RS
2603variables (C<$1>, ties) were not fixed till now [perl #57706].
2604
2605=item *
2606
2607Unary negation now treats strings consistently, regardless of the internal
2608C<UTF8> flag.
2609
2610=item *
2611
2612A regression introduced in Perl v5.16.0 involving
2613C<tr/I<SEARCHLIST>/I<REPLACEMENTLIST>/> has been fixed. Only the first
2614instance is supposed to be meaningful if a character appears more than
2615once in C<I<SEARCHLIST>>. Under some circumstances, the final instance
2616was overriding all earlier ones. [perl #113584]
2617
2618=item *
2619
2620Regular expressions like C<qr/\87/> previously silently inserted a NUL
2621character, thus matching as if it had been written C<qr/\00087/>. Now it
2622matches as if it had been written as C<qr/87/>, with a message that the
2623sequence C<"\8"> is unrecognized.
2624
2625=item *
2626
2627C<__SUB__> now works in special blocks (C<BEGIN>, C<END>, etc.).
2628
2629=item *
2630
2631Thread creation on Windows could theoretically result in a crash if done
2632inside a C<BEGIN> block. It still does not work properly, but it no longer
2633crashes [perl #111610].
2634
2635=item *
2636
2637C<\&{''}> (with the empty string) now autovivifies a stub like any other
2638sub name, and no longer produces the "Unable to create sub" error
2639[perl #94476].
2640
2641=item *
2642
2643A regression introduced in v5.14.0 has been fixed, in which some calls
2644to the C<re> module would clobber C<$_> [perl #113750].
2645
2646=item *
2647
2648C<do FILE> now always either sets or clears C<$@>, even when the file can't be
2649read. This ensures that testing C<$@> first (as recommended by the
2650documentation) always returns the correct result.
2651
2652=item *
2653
2654The array iterator used for the C<each @array> construct is now correctly
2655reset when C<@array> is cleared (RT #75596). This happens for example when the
2656array is globally assigned to, as in C<@array = (...)>, but not when its
2657B<values> are assigned to. In terms of the XS API, it means that C<av_clear()>
2658will now reset the iterator.
2659
2660This mirrors the behaviour of the hash iterator when the hash is cleared.
2661
2662=item *
2663
2664C<< $class->can >>, C<< $class->isa >>, and C<< $class->DOES >> now return
2665correct results, regardless of whether that package referred to by C<$class>
2666exists [perl #47113].
2667
2668=item *
2669
2670Arriving signals no longer clear C<$@> [perl #45173].
2671
2672=item *
2673
2674Allow C<my ()> declarations with an empty variable list [perl #113554].
2675
2676=item *
2677
2678During parsing, subs declared after errors no longer leave stubs
2679[perl #113712].
2680
2681=item *
2682
2683Closures containing no string evals no longer hang on to their containing
2684subroutines, allowing variables closed over by outer subroutines to be
2685freed when the outer sub is freed, even if the inner sub still exists
2686[perl #89544].
2687
2688=item *
2689
2690Duplication of in-memory filehandles by opening with a "<&=" or ">&=" mode
e612b5a0 2691stopped working properly in v5.16.0. It was causing the new handle to
5ed58cbd
RS
2692reference a different scalar variable. This has been fixed [perl #113764].
2693
2694=item *
2695
2696C<qr//> expressions no longer crash with custom regular expression engines
2697that do not set C<offs> at regular expression compilation time
2698[perl #112962].
2699
2700=item *
2701
2702C<delete local> no longer crashes with certain magical arrays and hashes
2703[perl #112966].
2704
2705=item *
2706
2707C<local> on elements of certain magical arrays and hashes used not to
2708arrange to have the element deleted on scope exit, even if the element did
2709not exist before C<local>.
2710
2711=item *
2712
2713C<scalar(write)> no longer returns multiple items [perl #73690].
2714
2715=item *
2716
2717String to floating point conversions no longer misparse certain strings under
2718C<use locale> [perl #109318].
2719
2720=item *
2721
2722C<@INC> filters that die no longer leak memory [perl #92252].
2723
2724=item *
2725
2726The implementations of overloaded operations are now called in the correct
2727context. This allows, among other things, being able to properly override
2728C<< <> >> [perl #47119].
2729
2730=item *
2731
2732Specifying only the C<fallback> key when calling C<use overload> now behaves
2733properly [perl #113010].
2734
2735=item *
2736
2737C<< sub foo { my $a = 0; while ($a) { ... } } >> and
2738C<< sub foo { while (0) { ... } } >> now return the same thing [perl #73618].
2739
2740=item *
2741
2742String negation now behaves the same under C<use integer;> as it does
2743without [perl #113012].
2744
2745=item *
2746
2747C<chr> now returns the Unicode replacement character (U+FFFD) for -1,
2748regardless of the internal representation. -1 used to wrap if the argument
2749was tied or a string internally.
2750
2751=item *
2752
2753Using a C<format> after its enclosing sub was freed could crash as of
e612b5a0 2754perl v5.12.0, if the format referenced lexical variables from the outer sub.
5ed58cbd
RS
2755
2756=item *
2757
2758Using a C<format> after its enclosing sub was undefined could crash as of
e612b5a0 2759perl v5.10.0, if the format referenced lexical variables from the outer sub.
5ed58cbd
RS
2760
2761=item *
2762
2763Using a C<format> defined inside a closure, which format references
2764lexical variables from outside, never really worked unless the C<write>
e612b5a0 2765call was directly inside the closure. In v5.10.0 it even started crashing.
5ed58cbd
RS
2766Now the copy of that closure nearest the top of the call stack is used to
2767find those variables.
2768
2769=item *
2770
2771Formats that close over variables in special blocks no longer crash if a
2772stub exists with the same name as the special block before the special
2773block is compiled.
2774
2775=item *
2776
2777The parser no longer gets confused, treating C<eval foo ()> as a syntax
2778error if preceded by C<print;> [perl #16249].
2779
2780=item *
2781
2782The return value of C<syscall> is no longer truncated on 64-bit platforms
2783[perl #113980].
2784
2785=item *
2786
2787Constant folding no longer causes C<print 1 ? FOO : BAR> to print to the
2788FOO handle [perl #78064].
2789
2790=item *
2791
2792C<do subname> now calls the named subroutine and uses the file name it
2793returns, instead of opening a file named "subname".
2794
2795=item *
2796
2797Subroutines looked up by rv2cv check hooks (registered by XS modules) are
2798now taken into consideration when determining whether C<foo bar> should be
2799the sub call C<foo(bar)> or the method call C<< "bar"->foo >>.
2800
2801=item *
2802
2803C<CORE::foo::bar> is no longer treated specially, allowing global overrides
2804to be called directly via C<CORE::GLOBAL::uc(...)> [perl #113016].
2805
2806=item *
2807
2808Calling an undefined sub whose typeglob has been undefined now produces the
2809customary "Undefined subroutine called" error, instead of "Not a CODE
2810reference".
2811
2812=item *
2813
2814Two bugs involving @ISA have been fixed. C<*ISA = *glob_without_array> and
2815C<undef *ISA; @{*ISA}> would prevent future modifications to @ISA from
2816updating the internal caches used to look up methods. The
e612b5a0 2817*glob_without_array case was a regression from Perl v5.12.
5ed58cbd
RS
2818
2819=item *
2820
2821Regular expression optimisations sometimes caused C<$> with C</m> to
2822produce failed or incorrect matches [perl #114068].
2823
2824=item *
2825
2826C<__SUB__> now works in a C<sort> block when the enclosing subroutine is
2827predeclared with C<sub foo;> syntax [perl #113710].
2828
2829=item *
2830
2831Unicode properties only apply to Unicode code points, which leads to
2832some subtleties when regular expressions are matched against
2833above-Unicode code points. There is a warning generated to draw your
2834attention to this. However, this warning was being generated
2835inappropriately in some cases, such as when a program was being parsed.
2836Non-Unicode matches such as C<\w> and C<[:word;]> should not generate the
2837warning, as their definitions don't limit them to apply to only Unicode
2838code points. Now the message is only generated when matching against
2839C<\p{}> and C<\P{}>. There remains a bug, [perl #114148], for the very
2840few properties in Unicode that match just a single code point. The
2841warning is not generated if they are matched against an above-Unicode
2842code point.
2843
2844=item *
2845
2846Uninitialized warnings mentioning hash elements would only mention the
2847element name if it was not in the first bucket of the hash, due to an
2848off-by-one error.
2849
2850=item *
2851
2852A regular expression optimizer bug could cause multiline "^" to behave
2853incorrectly in the presence of line breaks, such that
2854C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].
2855
2856=item *
2857
2858Failed C<fork> in list context no longer corrupts the stack.
2859C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
2860if the C<fork> call failed.
2861
2862=item *
2863
2864Numerous memory leaks have been fixed, mostly involving tied variables that
2865die, regular expression character classes and code blocks, and syntax
2866errors.
2867
2868=item *
2869
2870Assigning a regular expression (C<${qr//}>) to a variable that happens to
2871hold a floating point number no longer causes assertion failures on
2872debugging builds.
2873
2874=item *
2875
2876Assigning a regular expression to a scalar containing a number no longer
f105b7be 2877causes subsequent numification to produce random numbers.
5ed58cbd
RS
2878
2879=item *
2880
2881Assigning a regular expression to a magic variable no longer wipes away the
e612b5a0 2882magic. This was a regression from v5.10.
5ed58cbd
RS
2883
2884=item *
2885
2886Assigning a regular expression to a blessed scalar no longer results in
e612b5a0 2887crashes. This was also a regression from v5.10.
5ed58cbd
RS
2888
2889=item *
2890
2891Regular expression can now be assigned to tied hash and array elements with
2892flattening into strings.
2893
2894=item *
2895
f105b7be 2896Numifying a regular expression no longer results in an uninitialized
5ed58cbd
RS
2897warning.
2898
2899=item *
2900
2901Negative array indices no longer cause EXISTS methods of tied variables to
e612b5a0 2902be ignored. This was a regression from v5.12.
5ed58cbd
RS
2903
2904=item *
2905
2906Negative array indices no longer result in crashes on arrays tied to
2907non-objects.
2908
2909=item *
2910
be12dd22
RS
2911C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF-8 if the
2912left-hand scalar happened to have produced a UTF-8 string the last time
5ed58cbd
RS
2913overloading was invoked.
2914
2915=item *
2916
2917C<goto &sub> now uses the current value of @_, instead of using the array
2918the subroutine was originally called with. This means
2919C<local @_ = (...); goto &sub> now works [perl #43077].
2920
2921=item *
2922
2923If a debugger is invoked recursively, it no longer stomps on its own
2924lexical variables. Formerly under recursion all calls would share the same
2925set of lexical variables [perl #115742].
2926
2927=item *
2928
2929C<*_{ARRAY}> returned from a subroutine no longer spontaneously
2930becomes empty.
2931
2932=back
2933
2934=head1 Known Problems
2935
2936=over 4
2937
2938=item *
2939
7f50b25b 2940There are no known regressions. Please report any bugs you find!
5ed58cbd
RS
2941
2942=back
2943
2944=head1 Acknowledgements
a75569c0 2945
dd38235c
RS
2946Perl v5.18.0 represents approximately 12 months of development since
2947Perl v5.16.0 and contains approximately 400,000 lines of changes across
29482,100 files from 113 authors.
2949
2950Perl continues to flourish into its third decade thanks to a vibrant
2951community of users and developers. The following people are known to
2952have contributed the improvements that became Perl v5.18.0:
2953
2954Aaron Crane, Aaron Trevena, Abhijit Menon-Sen, Adrian M. Enache, Alan
2955Haggai Alavi, Alexandr Ciornii, Andrew Tam, Andy Dougherty, Anton Nikishaev,
2956Aristotle Pagaltzis, Augustina Blair, Bob Ernst, Brad Gilbert, Breno G. de
2957Oliveira, Brian Carlson, Brian Fraser, Charlie Gonzalez, Chip Salzenberg, Chris
2958'BinGOs' Williams, Christian Hansen, Colin Kuskie, Craig A. Berry, Dagfinn
2959Ilmari Mannsåker, Daniel Dragan, Daniel Perrett, Darin McBride, Dave Rolsky,
2960David Golden, David Leadbeater, David Mitchell, David Nicol, Dominic
2961Hargreaves, E. Choroba, Eric Brine, Evan Miller, Father Chrysostomos, Florian
2962Ragwitz, François Perrad, George Greer, Goro Fuji, H.Merijn Brand, Herbert
2963Breunung, Hugo van der Sanden, Igor Zaytsev, James E Keenan, Jan Dubois,
2964Jasmine Ahuja, Jerry D. Hedden, Jess Robinson, Jesse Luehrs, Joaquin Ferrero,
2965Joel Berger, John Goodyear, John Peacock, Karen Etheridge, Karl Williamson,
2966Karthik Rajagopalan, Kent Fredric, Leon Timmermans, Lucas Holt, Lukas Mai,
2967Marcus Holland-Moritz, Markus Jansen, Martin Hasch, Matthew Horsfall, Max
2968Maischein, Michael G Schwern, Michael Schroeder, Moritz Lenz, Nicholas Clark,
2969Niko Tyni, Oleg Nesterov, Patrik Hägglund, Paul Green, Paul Johnson, Paul
2970Marquess, Peter Martini, Rafael Garcia-Suarez, Reini Urban, Renee Baecker,
2971Rhesa Rozendaal, Ricardo Signes, Robin Barker, Ronald J. Kimball, Ruslan
2972Zakirov, Salvador Fandiño, Sawyer X, Scott Lanning, Sergey Alekseev, Shawn M
2973Moore, Shirakata Kentaro, Shlomi Fish, Sisyphus, Smylers, Steffen Müller,
2974Steve Hay, Steve Peters, Steven Schubiger, Sullivan Beck, Sven Strickroth,
2975Sébastien Aperghis-Tramoni, Thomas Sibley, Tobias Leich, Tom Wyant, Tony Cook,
2976Vadim Konovalov, Vincent Pit, Volker Schatz, Walt Mankowski, Yves Orton,
2977Zefram.
2978
2979The list above is almost certainly incomplete as it is automatically generated
2980from version control history. In particular, it does not include the names of
2981the (very much appreciated) contributors who reported issues to the Perl bug
2982tracker.
2983
2984Many of the changes included in this version originated in the CPAN modules
2985included in Perl's core. We're grateful to the entire CPAN community for
2986helping Perl to flourish.
2987
2988For a more complete list of all of Perl's historical contributors, please see
2989the F<AUTHORS> file in the Perl source distribution.
f5b73711 2990
44691e6f
AB
2991=head1 Reporting Bugs
2992
e08634c5
SH
2993If you find what you think is a bug, you might check the articles recently
2994posted to the comp.lang.perl.misc newsgroup and the perl bug database at
2995http://rt.perl.org/perlbug/ . There may also be information at
2996http://www.perl.org/ , the Perl Home Page.
44691e6f 2997
e08634c5
SH
2998If you believe you have an unreported bug, please run the L<perlbug> program
2999included with your release. Be sure to trim your bug down to a tiny but
3000sufficient test case. Your bug report, along with the output of C<perl -V>,
3001will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
44691e6f
AB
3002
3003If the bug you are reporting has security implications, which make it
e08634c5
SH
3004inappropriate to send to a publicly archived mailing list, then please send it
3005to perl5-security-report@perl.org. This points to a closed subscription
3006unarchived mailing list, which includes all the core committers, who will be
3007able to help assess the impact of issues, figure out a resolution, and help
f9001595 3008co-ordinate the release of patches to mitigate or fix the problem across all
e08634c5
SH
3009platforms on which Perl is supported. Please only use this address for
3010security issues in the Perl core, not for modules independently distributed on
3011CPAN.
44691e6f
AB
3012
3013=head1 SEE ALSO
3014
e08634c5
SH
3015The F<Changes> file for an explanation of how to view exhaustive details on
3016what changed.
44691e6f
AB
3017
3018The F<INSTALL> file for how to build Perl.
3019
3020The F<README> file for general stuff.
3021
3022The F<Artistic> and F<Copying> files for copyright information.
3023
3024=cut