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1=encoding utf8
2
3=head1 NAME
4
5ed58cbd 5perldelta - what is new for perl v5.18.0
e128ab2c 6
4eabcf70 7=head1 DESCRIPTION
6db9054f 8
5ed58cbd 9This document describes differences between the 5.16.0 release and the 5.18.0
e08634c5 10release.
6db9054f 11
d5f315e8 12If you are upgrading from an earlier release such as 5.14.0, first read
5ed58cbd 13L<perl5160delta>, which describes differences between 5.14.0 and 5.16.0.
3f01b192 14
5ed58cbd 15=head1 Core Enhancements
3f01b192 16
5ed58cbd 17=head2 New mechanism for experimental features
82d98f72 18
5ed58cbd 19Newly-added experimental features will now require this incantation:
82d98f72 20
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21 no warnings "experimental::feature_name";
22 use feature "feature_name"; # would warn without the prev line
23
24There is a new warnings category, called "experimental", containing
25warnings that the L<feature> pragma emits when enabling experimental
26features.
27
28Newly-added experimental features will also be given special warning IDs,
29which consist of "experimental::" followed by the name of the feature. (The
30plan is to extend this mechanism eventually to all warnings, to allow them
31to be enabled or disabled individually, and not just by category.)
32
33By saying
34
35 no warnings "experimental::feature_name";
36
37you are taking responsibility for any breakage that future changes to, or
38removal of, the feature may cause.
39
40Existing experimental features may begin emitting these warnings, too. Please
41consult L<perlexperiment> for information on which features are considered
42experimental.
43
44=head2 Hash overhaul
45
46Changes to the implementation of hashes in perl 5.18.0 will be one of the most
47visible changes to the behavior of existing code. For the most part, these
48changes will be visible as two distinct hash variables now providing their
49contents in a different order where it was previously identical. When
50encountering these changes, the key to cleaning up from them is to accept that
51B<hashes are unordered collections> and to act accordingly.
52
53=head3 Hash randomization
54
55The seed used by Perl's hash function is now random. This means that the
56order which keys/values will be returned from functions like C<keys()>,
57C<values()>, and C<each()> will differ from run to run.
58
59This change was introduced to make Perl's hashes more robust to algorithmic
60complexity attacks, and also because we discovered that it exposes hash
61ordering dependency bugs and makes them easier to track down.
62
63Toolchain maintainers might want to invest in additional infrastructure to
64test for things like this. Running tests several times in a row and then
65comparing results will make it easier to spot hash order dependencies in
66code. Authors are strongly encouraged not to expose the key order of
67Perl's hashes to insecure audiences.
68
69Further, every hash has its own iteration order, which should make it much
70more difficult to determine what the current hash seed is.
71
72=head3 New hash function: Murmurhash-32
73
74We have switched Perl's hash function to use Murmurhash-32, and added build
75support for several other hash functions. This new function is expected to
76perform equivalently to the old one for shorter strings and is faster for
77hashing longer strings.
78
79=head3 PERL_HASH_SEED enviornment variable now takes a hex value
80
81PERL_HASH_SEED no longer accepts an integer as a parameter, instead the
82value is expected to be a binary string encoded in hex. This is to make
83the infrastructure support hash seeds of arbitrary lengths which might
84exceed that of an integer. (SipHash uses a 16 byte seed).
85
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86=head3 PERL_PERTURB_KEYS environment variable added
87
88PERL_PERTURB_KEYS environment variable allows one to control the level of
89randomization applied to C<keys> and friends.
90
91When PERL_PERTURB_KEYS is 0, perl will not randomize key order at all. The
92chance that C<keys> changes due to an insert will be the same as in previous
93perls, basically only when the bucket size is changed.
94
95When PERL_PERTURB_KEYS is 1, perl will randomize keys in a non repeatedable
96way. The chance that C<keys> changes due to an insert will be very high. This
97is the most secure and default mode.
98
99When PERL_PERTURB_KEYS is 2, perl will randomize keys in a repeatedable way.
100Repititive runs of the same program should produce the same output every time.
101The chance that keys changes due to an insert will be very high.
102
103PERL_HASH_SEED implies a non-default PERL_PERTURB_KEYS setting. Setting
104PERL_HASH_SEED=0 (exactly one 0) implies PERL_PERTURB_KEYS=0 (hash key
105randomization disabled), settng PERL_HASH_SEED to any other value, implies
106PERL_PERTURB_KEYS=2 (deterministic/repeatable hash key randomization).
107Specifying PERL_PERTURB_KEYS explicitly to a different level overrides this
108behavior.
109
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110=head3 Hash::Util::hash_seed() now returns a string
111
112Hash::Util::hash_seed() now returns a string instead of an integer. This
113is to make the infrastructure support hash seeds of arbitrary lengths
114which might exceed that of an integer. (SipHash uses a 16 byte seed).
115
116=head3 Output of PERL_HASH_SEED_DEBUG has been changed
117
118The environment variable PERL_HASH_SEED_DEBUG now makes perl show both the
119hash function perl was built with AND the seed, in hex, in use for that
120process. Code parsing this output, should it exist, must change to accommodate
121the new format. Example of the new format:
122
123 $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
124 HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f
125
126=head2 Upgrade to Unicode 6.2
127
2e7bc647 128Perl now supports Unicode 6.2. A list of changes from Unicode
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1296.1 is at L<http://www.unicode.org/versions/Unicode6.2.0>.
130
131=head2 Character name aliases may now include non-Latin1-range characters
132
133It is possible to define your own names for characters for use in
134C<\N{...}>, C<charnames::vianame()>, etc. These names can now be
135comprised of characters from the whole Unicode range. This allows for
136names to be in your native language, and not just English. Certain
137restrictions apply to the characters that may be used (you can't define
138a name that has punctuation in it, for example). See L<charnames/CUSTOM
139ALIASES>.
140
141=head2 New DTrace probes
142
143The following new DTrace probes have been added:
14731ad1 144
337fb649 145=over 4
14731ad1 146
82d98f72 147=item *
14731ad1 148
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149C<op-entry>
150
151=item *
152
153C<loading-file>
154
155=item *
156
157C<loaded-file>
158
159=back
160
161=head2 C<${^LAST_FH}>
162
163This new variable provides access to the filehandle that was last read.
164This is the handle used by C<$.> and by C<tell> and C<eof> without
165arguments.
166
167=head2 Regular Expression Set Operations
168
169This is an B<experimental> feature to allow matching against the union,
170intersection, etc., of sets of code points, similar to
171L<Unicode::Regex::Set>. It can also be used to extend C</x> processing
172to [bracketed] character classes, and as a replacement of user-defined
173properties, allowing more complex expressions than they do. See
174L<perlrecharclass/Extended Bracketed Character Classes>.
175
176=head2 Lexical subroutines
177
178This new feature is still considered B<experimental>. To enable it:
179
180 use 5.018;
181 no warnings "experimental::lexical_subs";
182 use feature "lexical_subs";
183
184You can now declare subroutines with C<state sub foo>, C<my sub foo>, and
185C<our sub foo>. (C<state sub> requires that the "state" feature be
186enabled, unless you write it as C<CORE::state sub foo>.)
187
188C<state sub> creates a subroutine visible within the lexical scope in which
189it is declared. The subroutine is shared between calls to the outer sub.
190
191C<my sub> declares a lexical subroutine that is created each time the
192enclosing block is entered. C<state sub> is generally slightly faster than
193C<my sub>.
194
195C<our sub> declares a lexical alias to the package subroutine of the same
196name.
197
198For more information, see L<perlsub/Lexical Subroutines>.
199
200=head2 Computed Labels
201
202The loop controls C<next>, C<last> and C<redo>, and the special C<dump>
203operator, now allow arbitrary expressions to be used to compute labels at run
204time. Previously, any argument that was not a constant was treated as the
205empty string.
206
207=head2 More CORE:: subs
208
209Several more built-in functions have been added as subroutines to the
210CORE:: namespace - namely, those non-overridable keywords that can be
211implemented without custom parsers: C<defined>, C<delete>, C<exists>,
212C<glob>, C<pos>, C<protoytpe>, C<scalar>, C<split>, C<study>, and C<undef>.
213
214As some of these have prototypes, C<prototype('CORE::...')> has been
215changed to not make a distinction between overridable and non-overridable
216keywords. This is to make C<prototype('CORE::pos')> consistent with
217C<prototype(&CORE::pos)>.
218
219=head2 C<kill> with negative signal names
220
221C<kill> has always allowed a negative signal number, which kills the
222process group instead of a single process. It has also allowed signal
223names. But it did not behave consistently, because negative signal names
224were treated as 0. Now negative signals names like C<-INT> are supported
225and treated the same way as -2 [perl #112990].
226
227=head1 Security
228
229=head2 C<Storable> security warning in documentation
230
231The documentation for C<Storable> now includes a section which warns readers
232of the danger of accepting Storable documents from untrusted sources. The
233short version is that deserializing certain types of data can lead to loading
234modules and other code execution. This is documented behavior and wanted
235behavior, but this opens an attack vector for malicious entities.
236
237=head2 C<Locale::Maketext> allowed code injection via a malicious template
238
239If users could provide a translation string to Locale::Maketext, this could be
240used to invoke arbitrary Perl subroutines available in the current process.
241
242This has been fixed, but it is still possible to invoke any method provided by
243C<Locale::Maketext> itself or a subclass that you are using. One of these
244methods in turn will invoke the Perl core's C<sprintf> subroutine.
245
246In summary, allowing users to provide translation strings without auditing
247them is a bad idea.
248
249This vulnerability is documented in CVE-2012-6329.
250
251=head2 Avoid calling memset with a negative count
252
253Poorly written perl code that allows an attacker to specify the count to perl's
254C<x> string repeat operator can already cause a memory exhaustion
255denial-of-service attack. A flaw in versions of perl before 5.15.5 can escalate
256that into a heap buffer overrun; coupled with versions of glibc before 2.16, it
257possibly allows the execution of arbitrary code.
258
259The flaw addressed to this commit has been assigned identifier CVE-2012-5195
260and was researched by Tim Brown.
261
262=head1 Incompatible Changes
263
264=head2 See also: hash overhaul
265
266Some of the changes in the L<hash overhaul|/"Hash overhaul"> are not fully
267compatible with previous versions of perl. Please read that section.
268
269=head2 An unknown character name in C<\N{...}> is now a syntax error
270
271Previously, it warned, and the Unicode REPLACEMENT CHARACTER was
272substituted. Unicode now recommends that this situation be a syntax
273error. Also, the previous behavior led to some confusing warnings and
274behaviors, and since the REPLACEMENT CHARACTER has no use other than as
275a stand-in for some unknown character, any code that has this problem is
276buggy.
277
278=head2 Formerly deprecated characters in C<\N{}> character name aliases are now errors.
279
280Since v5.12.0, it has been deprecated to use certain characters in
281user-defined C<\N{...}> character names. These now cause a syntax
282error. For example, it is now an error to begin a name with a digit,
283such as in
284
285 my $undraftable = "\N{4F}"; # Syntax error!
286
287or to have commas anywhere in the name. See L<charnames/CUSTOM ALIASES>
288
289=head2 C<\N{BELL}> now refers to U+1F514 instead of U+0007
290
291Unicode 6.0 reused the name "BELL" for a different code point than it
292traditionally had meant. Since Perl v5.14, use of this name still
293referred to U+0007, but would raise a deprecation warning. Now, "BELL"
294refers to U+1F514, and the name for U+0007 is "ALERT". All the
295functions in L<charnames> have been correspondingly updated.
296
297=head2 New Restrictions in Multi-Character Case-Insensitive Matching in Regular Expression Bracketed Character Classes
298
299Unicode has now withdrawn their previous recommendation for regular
300expressions to automatically handle cases where a single character can
301match multiple characters case-insensitively, for example the letter
302LATIN SMALL LETTER SHARP S and the sequence C<ss>. This is because
303it turns out to be impracticable to do this correctly in all
304circumstances. Because Perl has tried to do this as best it can, it
305will continue to do so. (We are considering an option to turn it off.)
306However, a new restriction is being added on such matches when they
307occur in [bracketed] character classes. People were specifying
308things such as C</[\0-\xff]/i>, and being surprised that it matches the
309two character sequence C<ss> (since LATIN SMALL LETTER SHARP S occurs in
310this range). This behavior is also inconsistent with using a
311property instead of a range: C<\p{Block=Latin1}> also includes LATIN
312SMALL LETTER SHARP S, but C</[\p{Block=Latin1}]/i> does not match C<ss>.
313The new rule is that for there to be a multi-character case-insensitive
314match within a bracketed character class, the character must be
315explicitly listed, and not as an end point of a range. This more
316closely obeys the Principle of Least Astonishment. See
317L<perlrecharclass/Bracketed Character Classes>. Note that a bug [perl
318#89774], now fixed as part of this change, prevented the previous
319behavior from working fully.
320
321=head2 Explicit rules for variable names and identifiers
322
323Due to an oversight, length-one variable names in 5.16 were completely
324unrestricted, and opened the door to several kinds of insanity. As of
3255.18, these now follow the rules of other identifiers, in addition
326to accepting characters that match the C<\p{POSIX_Punct}> property.
327
328There are no longer any differences in the parsing of identifiers
329specified as C<$...> or C<${...}>; previously, they were dealt with in
330different parts of the core, and so had slightly different behavior. For
331instance, C<${foo:bar}> was a legal variable name. Since they are now
332both parsed by the same code, that is no longer the case.
333
334=head2 C<\s> in regular expressions now matches a Vertical Tab
335
336No one could recall why C<\s> didn't match C<\cK>, the vertical tab.
337Now it does. Given the extreme rarity of that character, very little
338breakage is expected.
339
340=head2 C</(?{})/> and C</(??{})/> have been heavily reworked
341
342The implementation of this feature has been almost completely rewritten.
343Although its main intent is to fix bugs, some behaviors, especially
344related to the scope of lexical variables, will have changed. This is
345described more fully in the L</Selected Bug Fixes> section.
346
347=head2 Stricter parsing of substitution replacement
348
349It is no longer possible to abuse the way the parser parses C<s///e> like
350this:
351
352 %_=(_,"Just another ");
353 $_="Perl hacker,\n";
354 s//_}->{_/e;print
355
356=head2 C<given> now aliases the global C<$_>
357
358Instead of assigning to an implicit lexical C<$_>, C<given> now makes the
359global C<$_> an alias for its argument, just like C<foreach>. However, it
360still uses lexical C<$_> if there is lexical C<$_> in scope (again, just like
361C<foreach>) [perl #114020].
362
363=head2 Lexical C<$_> is now experimental
364
365Since it was introduced in Perl 5.10, it has caused much confusion with no
366obvious solution:
367
368=over
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369
370=item *
371
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372Various modules (e.g., List::Util) expect callback routines to use the
373global C<$_>. C<use List::Util 'first'; my $_; first { $_ == 1 } @list>
374does not work as one would expect.
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375
376=item *
377
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378A C<my $_> declaration earlier in the same file can cause confusing closure
379warnings.
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380
381=item *
382
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383The "_" subroutine prototype character allows called subroutines to access
384your lexical C<$_>, so it is not really private after all.
2426c394 385
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386=item *
387
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388Nevertheless, subroutines with a "(@)" prototype and methods cannot access
389the caller's lexical C<$_>, unless they are written in XS.
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390
391=item *
392
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393But even XS routines cannot access a lexical C<$_> declared, not in the
394calling subroutine, but in an outer scope, iff that subroutine happened not
395to mention C<$_> or use any operators that default to C<$_>.
396
397=back
398
399It is our hope that lexical C<$_> can be rehabilitated, but this may
400cause changes in its behavior. Please use it with caution until it
401becomes stable.
402
403=head2 readline() with C<$/ = \N> now reads N characters, not N bytes
404
405Previously, when reading from a stream with I/O layers such as
406C<encoding>, the readline() function, otherwise known as the C<< <> >>
407operator, would read I<N> bytes from the top-most layer. [perl #79960]
408
409Now, I<N> characters are read instead.
410
411There is no change in behaviour when reading from streams with no
412extra layers, since bytes map exactly to characters.
413
414=head2 Overridden C<glob> is now passed one argument
415
416C<glob> overrides used to be passed a magical undocumented second argument
417that identified the caller. Nothing on CPAN was using this, and it got in
418the way of a bug fix, so it was removed. If you really need to identify
419the caller, see L<Devel::Callsite> on CPAN.
420
421=head2 Here-doc parsing
422
423The body of a here-document inside a quote-like operator now always begins
424on the line after the "<<foo" marker. Previously, it was documented to
425begin on the line following the containing quote-like operator, but that
426was only sometimes the case [perl #114040].
427
428=head2 Alphanumeric operators must now be separated from the closing
429delimiter of regular expressions
430
431You may no longer write something like:
432
433 m/a/and 1
434
435Instead you must write
436
437 m/a/ and 1
438
439with whitespace separating the operator from the closing delimiter of
440the regular expression. Not having whitespace has resulted in a
441deprecation warning since Perl v5.14.0.
442
443=head2 qw(...) can no longer be used as parentheses
444
445C<qw> lists used to fool the parser into thinking they were always
446surrounded by parentheses. This permitted some surprising constructions
447such as C<foreach $x qw(a b c) {...}>, which should really be written
448C<foreach $x (qw(a b c)) {...}>. These would sometimes get the lexer into
449the wrong state, so they didn't fully work, and the similar C<foreach qw(a
450b c) {...}> that one might expect to be permitted never worked at all.
451
452This side effect of C<qw> has now been abolished. It has been deprecated
453since Perl 5.13.11. It is now necessary to use real parentheses
454everywhere that the grammar calls for them.
455
456=head2 Interaction of lexical and default warnings
457
458Turning on any lexical warnings used first to disable all default warnings
459if lexical warnings were not already enabled:
460
461 $*; # deprecation warning
462 use warnings "void";
463 $#; # void warning; no deprecation warning
464
465Now, the debugging, deprecated, glob, inplace and malloc warnings
466categories are left on when turning on lexical warnings (unless they are
467turned off by C<no warnings>, of course).
468
469This may cause deprecation warnings to occur in code that used to be free
470of warnings.
471
472Those are the only categories consisting only of default warnings. Default
473warnings in other categories are still disabled by C<use warnings
474"category">, as we do not yet have the infrastructure for controlling
475individual warnings.
476
477=head2 C<state sub> and C<our sub>
478
479Due to an accident of history, C<state sub> and C<our sub> were equivalent
480to a plain C<sub>, so one could even create an anonymous sub with
481C<our sub { ... }>. These are now disallowed outside of the "lexical_subs"
482feature. Under the "lexical_subs" feature they have new meanings described
483in L<perlsub/Lexical Subroutines>.
484
485=head2 Defined values stored in environment are forced to byte strings
486
487A value stored in an environment variable has always been stringified. In this
488release, it is converted to be only a byte string. First, it is forced to be a
489only a string. Then if the string is utf8 and the equivalent of
490C<utf8::downgrade()> works, that result is used; otherwise, the equivalent of
491C<utf8::encode()> is used, and a warning is issued about wide characters
492(L</Diagnostics>).
493
494=head2 C<require> dies for unreadable files
495
496When C<require> encounters an unreadable file, it now dies. It used to
497ignore the file and continue searching the directories in C<@INC>
498[perl #113422].
499
500=head2 C<gv_fetchmeth_*> and SUPER
501
502The various C<gv_fetchmeth_*> XS functions used to treat a package whose
503named ended with ::SUPER specially. A method lookup on the Foo::SUPER
504package would be treated as a SUPER method lookup on the Foo package. This
505is no longer the case. To do a SUPER lookup, pass the Foo stash and the
506GV_SUPER flag.
507
508=head2 C<split>'s first argument is more consistently interpreted
509
510After some changes earlier in 5.17, C<split>'s behavior has been
511simplified: if the PATTERN argument evaluates to a literal string
512containing one space, it is treated the way that a I<literal> string
513containing one space once was.
514
515=head1 Deprecations
516
517=head2 Deprecated modules
518
519The following modules will be removed from the core distribution in a
520future release, and should be installed from CPAN instead. Distributions
521on CPAN which require these should add them to their prerequisites.
522The core versions of these modules will issue "deprecated"-category
523warnings.
524
525You can silence these deprecation warnings by installing the modules
526in question from CPAN.
527
528=over
529
530=item L<Archive::Extract>
531
532=item L<B::Lint>
533
534=item L<B::Lint::Debug>
535
536=item L<CPANPLUS> and all included C<CPANPLUS::*> modules
537
538=item L<Devel::InnerPackage>
539
540=item L<encoding>
541
542=item L<Log::Message>
543
544=item L<Log::Message::Config>
545
546=item L<Log::Message::Handlers>
547
548=item L<Log::Message::Item>
549
550=item L<Log::Message::Simple>
551
552=item L<Module::Pluggable>
553
554=item L<Module::Pluggable::Object>
555
556=item L<Object::Accessor>
557
558=item L<Pod::LaTeX>
559
560=item L<Term::UI>
561
562=item L<Term::UI::History>
563
564=back
565
566=head2 Deprecated Utilities
567
568The following utilities will be removed from the core distribution in a
569future release as their associated modules have been deprecated. They
570will remain available with the applicable CPAN distribution.
571
572=over
573
574=item L<cpanp>
575
576=item C<cpanp-run-perl>
577
578=item L<cpan2dist>
579
580These items are part of the C<CPANPLUS> distribution.
581
582=item L<pod2latex>
583
584This item is part of the C<Pod::LaTeX> distribution.
585
586=back
587
588=head2 PL_sv_objcount
589
590This interpreter-global variable used to track the total number of
591Perl objects in the interpreter. It is no longer maintained and will
592be removed altogether in Perl 5.20.
593
594=head2 Five additional characters should be escaped in patterns with C</x>
595
596When a regular expression pattern is compiled with C</x>, Perl treats 6
597characters as white space to ignore, such as SPACE and TAB. However,
598Unicode recommends 11 characters be treated thusly. We will conform
599with this in a future Perl version. In the meantime, use of any of the
600missing characters will raise a deprecation warning, unless turned off.
601The five characters are:
602U+0085 NEXT LINE,
603U+200E LEFT-TO-RIGHT MARK,
604U+200F RIGHT-TO-LEFT MARK,
605U+2028 LINE SEPARATOR,
606and
607U+2029 PARAGRAPH SEPARATOR.
608
609=head2 User-defined charnames with surprising whitespace
610
611A user-defined character name with trailing or multiple spaces in a row is
612likely a typo. This now generates a warning when defined, on the assumption
613that uses of it will be unlikely to include the excess whitespace.
614
615=head2 Various XS-callable functions are now deprecated
616
617All the functions used to classify characters will be removed from a
618future version of Perl, and should not be used. With participating C
619compilers (e.g., gcc), compiling any file that uses any of these will
620generate a warning. These were not intended for public use; there are
621equivalent, faster, macros for most of them.
2e7bc647 622See L<perlapi/Character classes>. The complete list is:
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623C<is_uni_alnum>, C<is_uni_alnumc>, C<is_uni_alnumc_lc>,
624C<is_uni_alnum_lc>, C<is_uni_alpha>, C<is_uni_alpha_lc>,
625C<is_uni_ascii>, C<is_uni_ascii_lc>, C<is_uni_blank>,
626C<is_uni_blank_lc>, C<is_uni_cntrl>, C<is_uni_cntrl_lc>,
627C<is_uni_digit>, C<is_uni_digit_lc>, C<is_uni_graph>,
628C<is_uni_graph_lc>, C<is_uni_idfirst>, C<is_uni_idfirst_lc>,
629C<is_uni_lower>, C<is_uni_lower_lc>, C<is_uni_print>,
630C<is_uni_print_lc>, C<is_uni_punct>, C<is_uni_punct_lc>,
631C<is_uni_space>, C<is_uni_space_lc>, C<is_uni_upper>,
632C<is_uni_upper_lc>, C<is_uni_xdigit>, C<is_uni_xdigit_lc>,
633C<is_utf8_alnum>, C<is_utf8_alnumc>, C<is_utf8_alpha>,
634C<is_utf8_ascii>, C<is_utf8_blank>, C<is_utf8_char>,
635C<is_utf8_cntrl>, C<is_utf8_digit>, C<is_utf8_graph>,
636C<is_utf8_idcont>, C<is_utf8_idfirst>, C<is_utf8_lower>,
637C<is_utf8_mark>, C<is_utf8_perl_space>, C<is_utf8_perl_word>,
638C<is_utf8_posix_digit>, C<is_utf8_print>, C<is_utf8_punct>,
639C<is_utf8_space>, C<is_utf8_upper>, C<is_utf8_xdigit>,
640C<is_utf8_xidcont>, C<is_utf8_xidfirst>.
641
642In addition these three functions that have never worked properly are
643deprecated:
644C<to_uni_lower_lc>, C<to_uni_title_lc>, and C<to_uni_upper_lc>.
645
646=head2 Certain rare uses of backslashes within regexes are now deprectated
647
648There are three pairs of characters that Perl recognizes as
649metacharacters in regular expression patterns: C<{}>, C<[]>, and C<()>.
650These can be used as well to delimit patterns, as in:
651
652 m{foo}
653 s(foo)(bar)
654
655Since they are metacharacters, they have special meaning to regular
656expression patterns, and it turns out that you can't turn off that
657special meaning by the normal means of preceding them with a backslash,
658if you use them, paired, within a pattern delimitted by them. For
659example, in
660
661 m{foo\{1,3\}}
662
663the backslashes do not change the behavior, and this matches
664S<C<"f o">> followed by one to three more occurrences of C<"o">.
665
666Usages like this, where they are interpreted as metacharacters, are
667exceedingly rare; we think there are none, for example, in all of CPAN.
668Hence, this deprecation should affect very little code. It does give
669notice, however, that any such code needs to change, which will in turn
670allow us to change the behavior in future Perl versions so that the
671backslashes do have an effect, and without fear that we are silently
672breaking any existing code.
673
d5f315e8
KW
674=head2 Splitting the tokens C<(?> and C<(*> in regular expressions
675
676A deprecation warning is now raised if the C<(> and C<?> are separated
677by white space or comments in C<(?...)> regular expression constructs.
678Similarly, if the C<(> and C<*> are separated in C<(*VERB...)>
679constructs.
680
e0a1dec5
LT
681=head2 Pre-PerlIO IO implementations
682
683Perl supports being built without PerlIO proper, using a stdio or sfio
684wrapper instead. A perl build like this will not support IO layers and
685thus Unicode IO, making it rather handicapped.
686
687PerlIO supports a C<stdio> layer if stdio use is desired, and similarly a
688sfio layer could be produced.
689
5ed58cbd
RS
690=head1 Future Deprecations
691
692=over
71e6aba6
RS
693
694=item *
695
4263dd11 696Platforms without support infrastructure
5ed58cbd
RS
697
698Both Windows CE and z/OS have been historically under-maintained, and are
699currently neither successfully building nor regularly being smoke tested.
700Efforts are underway to change this situation, but it should not be taken for
701granted that the platforms are safe and supported. If they do not become
702buildable and regularly smoked, support for them may be actively removed in
703future releases. If you have an interest in these platforms and you can lend
704your time, expertise, or hardware to help support these platforms, please let
705the perl development effort know by emailing C<perl5-porters@perl.org>.
706
707Some platforms that appear otherwise entirely dead are also on the short list
708for removal between now and 5.20.0:
709
710=over
711
712=item DG/UX
713
714=item NeXT
715
716=back
1993add8
RS
717
718=item *
719
5ed58cbd
RS
720Swapping of $< and $>
721
722For more information about this future deprecation, see L<the relevant RT
723ticket|https://rt.perl.org/rt3/Ticket/Display.html?id=96212>.
71e6aba6
RS
724
725=item *
726
5ed58cbd 727C<microperl>, long broken and of unclear present purpose, will be removed.
71e6aba6
RS
728
729=item *
730
5ed58cbd
RS
731Revamping C<< "\Q" >> semantics in double-quotish strings when combined with
732other escapes.
733
734There are several bugs and inconsistencies involving combinations
735of C<\Q> and escapes like C<\x>, C<\L>, etc., within a C<\Q...\E> pair.
736These need to be fixed, and doing so will necessarily change current
737behavior. The changes have not yet been settled.
71e6aba6 738
d5f315e8
KW
739=item *
740
741Use of C<$^>, where C<^> stands for any actual (non-printing) C0 control
742character will be disallowed in a future Perl version. Use C<${^}>
743instead (where again C<^> stands for a control character),
744or better, C<$^A> , where C<^> this time is a caret (CIRCUMFLEX ACCENT),
745and C<A> stands for any of the characters listed at the end of
746L<perlebcdic/OPERATOR DIFFERENCES>.
747
337fb649 748=back
2426c394 749
5ed58cbd
RS
750=head1 Performance Enhancements
751
752=over 4
2426c394 753
5ed58cbd 754=item *
2426c394 755
5ed58cbd
RS
756Lists of lexical variable declarations (C<my($x, $y)>) are now optimised
757down to a single op and are hence faster than before.
2426c394 758
5ed58cbd 759=item *
2426c394 760
5ed58cbd
RS
761A new C preprocessor define C<NO_TAINT_SUPPORT> was added that, if set,
762disables Perl's taint support altogether. Using the -T or -t command
763line flags will cause a fatal error. Beware that both core tests as
764well as many a CPAN distribution's tests will fail with this change. On
765the upside, it provides a small performance benefit due to reduced
766branching.
2426c394 767
5ed58cbd
RS
768B<Do not enable this unless you know exactly what you are getting yourself
769into.>
770
771=item *
772
773C<pack> with constant arguments is now constant folded in most cases
774[perl #113470].
775
776=item *
777
778Speed up in regular expression matching against Unicode properties. The
779largest gain is for C<\X>, the Unicode "extended grapheme cluster." The
780gain for it is about 35% - 40%. Bracketed character classes, e.g.,
781C<[0-9\x{100}]> containing code points above 255 are also now faster.
782
783=item *
784
785On platforms supporting it, several former macros are now implemented as static
786inline functions. This should speed things up slightly on non-GCC platforms.
787
788=item *
789
790Apply the optimisation of hashes in boolean context, such as in C<if> or
791C<and>, to constructs in non-void context.
792
793=item *
794
795Extend the optimisation of hashes in boolean context to C<scalar(%hash)>,
796C<%hash ? ... : ...>, and C<sub { %hash || ... }>.
797
798=item *
799
800Filetest ops manage the stack in a fractionally more efficient manner.
801
802=item *
803
804Globs used in a numeric context are now numified directly in most cases,
805rather than being numerified via stringification.
806
807=item *
808
809The C<x> repetition operator is now folded to a single constant at compile
810time if called in scalar context with constant operands and no parentheses
811around the left operand.
812
813=back
814
815=head1 Modules and Pragmata
816
817=head2 New Modules and Pragmata
2426c394 818
337fb649 819=over 4
982110e0 820
82d98f72 821=item *
2426c394 822
5ed58cbd
RS
823L<Config::Perl::V> version 0.16 has been added as a dual-lifed module.
824It provides structured data retrieval of C<perl -V> output including
825information only known to the C<perl> binary and not available via L<Config>.
826
827=back
828
829=head2 Updated Modules and Pragmata
830
831This is only an overview of selected module updates. For a complete
832list of updates, run:
833
834 $ corelist --diff 5.14.0 5.16.0
835
836You can substitute your favorite version in place of 5.14.0, too.
837
838=over 4
33392251
BF
839
840=item *
841
5ed58cbd
RS
842L<XXX> has been upgraded from version A.xx to B.yy.
843
844=back
845
846=head2 Removed Modules and Pragmata
847
848=over
33392251
BF
849
850=item *
851
5ed58cbd
RS
852L<Version::Requirements> has been removed from the core distribution. It is
853available under a different name: L<CPAN::Meta::Requirements>.
2426c394 854
337fb649 855=back
2426c394 856
5ed58cbd 857=head1 Documentation
19718730 858
5ed58cbd
RS
859=head2 Changes to Existing Documentation
860
861=head3 L<perlcheat>
82d98f72 862
5a6a30f4 863=over 4
b7c7d786 864
5ed58cbd
RS
865=item *
866
867L<perlcheat> has been reorganized, and a few new sections were added.
868
869=back
870
871=head3 L<perldata>
872
873=over 4
82d98f72 874
5ed58cbd 875=item *
d2d1e842 876
5ed58cbd
RS
877Now explicitly documents the behaviour of hash initializer lists that
878contain duplicate keys.
f355e93d 879
5a6a30f4 880=back
f355e93d 881
5ed58cbd 882=head3 L<perldiag>
19718730 883
19718730 884=over 4
e14ac59b 885
5ed58cbd
RS
886=item *
887
888The explanation of symbolic references being prevented by "strict refs"
889now doesn't assume that the reader knows what symbolic references are.
890
891=back
9f351b45 892
5ed58cbd 893=head3 L<perlfaq>
9f351b45 894
5ed58cbd 895=over 4
9f351b45 896
5ed58cbd 897=item *
7cf3104f 898
5ed58cbd 899L<perlfaq> has been synchronized with version 5.0150040 from CPAN.
12719193 900
6253ee75 901=back
216cf7fc 902
5ed58cbd 903=head3 L<perlfunc>
f5b73711 904
5ed58cbd
RS
905=over 4
906
907=item *
a75569c0 908
5ed58cbd 909The return value of C<pipe> is now documented.
a75569c0 910
5ed58cbd 911=item *
a75569c0 912
5ed58cbd
RS
913Clarified documentation of C<our>.
914
915=back
916
917=head3 L<perlop>
918
919=over 4
920
921=item *
922
923Loop control verbs (C<dump>, C<goto>, C<next>, C<last> and C<redo>) have always
924had the same precedence as assignment operators, but this was not documented
925until now.
926
927=back
928
929=head3 Diagnostics
930
931The following additions or changes have been made to diagnostic output,
932including warnings and fatal error messages. For the complete list of
933diagnostic messages, see L<perldiag>.
934
935XXX New or changed warnings emitted by the core's C<C> code go here. Also
936include any changes in L<perldiag> that reconcile it to the C<C> code.
937
938=head2 New Diagnostics
939
940XXX Newly added diagnostic messages go under here, separated into New Errors
941and New Warnings
942
943=head3 New Errors
944
945=over 4
946
947=item *
948
949L<Unterminated delimiter for here document|perldiag/"Unterminated delimiter for here document">
950
951This message now occurs when a here document label has an initial quotation
952mark but the final quotation mark is missing.
953
954This replaces a bogus and misleading error message about not finding the label
955itself [perl #114104].
956
957=item *
958
959L<panic: child pseudo-process was never scheduled|perldiag/"panic: child pseudo-process was never scheduled">
960
961This error is thrown when a child pseudo-process in the ithreads implementation
962on Windows was not scheduled within the time period allowed and therefore was
963not able to initialize properly [perl #88840].
964
965=item *
966
967L<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/">
968
969This error has been added for C<(?&0)>, which is invalid. It used to
970produce an incomprehensible error message [perl #101666].
971
972=item *
973
974L<Can't use an undefined value as a subroutine reference|perldiag/"Can't use an undefined value as %s reference">
975
976Calling an undefined value as a subroutine now produces this error message.
977It used to, but was accidentally disabled, first in Perl 5.004 for
978non-magical variables, and then in Perl 5.14 for magical (e.g., tied)
979variables. It has now been restored. In the mean time, undef was treated
980as an empty string [perl #113576].
981
982=item *
983
984L<Experimental "%s" subs not enabled|perldiag/"Experimental "%s" subs not enabled">
985
986To use lexical subs, you must first enable them:
987
988 no warnings 'experimental::lexical_subs';
989 use feature 'lexical_subs';
990 my sub foo { ... }
991
992=back
993
994=head3 New Warnings
995
996=over 4
997
998=item *
999
1000XXX: This needs more detail.
1001
1002Strings with code points over 0xFF may not be mapped into in-memory file
1003handles
1004
1005=item *
1006
1007L<'%s' resolved to '\o{%s}%d'|perldiag/"'%s' resolved to '\o{%s}%d'">
1008
1009=item *
1010
1011L<'Trailing white-space in a charnames alias definition is deprecated'|perldiag/"Trailing white-space in a charnames alias definition is deprecated">
1012
1013=item *
1014
1015L<'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">
1016
1017=item *
1018
1019L<'Passing malformed UTF-8 to "%s" is deprecated'|perldiag/"Passing malformed UTF-8 to "%s" is deprecated">
1020
1021=item *
1022
1023L<Subroutine "&%s" is not available|perldiag/"Subroutine "&%s" is not available">
1024
1025(W closure) During compilation, an inner named subroutine or eval is
1026attempting to capture an outer lexical subroutine that is not currently
1027available. This can happen for one of two reasons. First, the lexical
1028subroutine may be declared in an outer anonymous subroutine that has not
1029yet been created. (Remember that named subs are created at compile time,
1030while anonymous subs are created at run-time.) For example,
1031
1032 sub { my sub a {...} sub f { \&a } }
1033
1034At the time that f is created, it can't capture the current the "a" sub,
1035since the anonymous subroutine hasn't been created yet. Conversely, the
1036following won't give a warning since the anonymous subroutine has by now
1037been created and is live:
1038
1039 sub { my sub a {...} eval 'sub f { \&a }' }->();
1040
1041The second situation is caused by an eval accessing a variable that has
1042gone out of scope, for example,
1043
1044 sub f {
1045 my sub a {...}
1046 sub { eval '\&a' }
1047 }
1048 f()->();
1049
1050Here, when the '\&a' in the eval is being compiled, f() is not currently
1051being executed, so its &a is not available for capture.
1052
1053=item *
1054
1055L<"%s" subroutine &%s masks earlier declaration in same %s|perldiag/"%s" subroutine &%s masks earlier declaration in same %s>
1056
1057(W misc) A "my" or "state" subroutine has been redeclared in the
1058current scope or statement, effectively eliminating all access to
1059the previous instance. This is almost always a typographical error.
1060Note that the earlier subroutine will still exist until the end of
1061the scope or until all closure references to it are destroyed.
1062
1063=item *
1064
1065L<The %s feature is experimental|perldiag/"The %s feature is experimental">
1066
1067(S experimental) This warning is emitted if you enable an experimental
1068feature via C<use feature>. Simply suppress the warning if you want
1069to use the feature, but know that in doing so you are taking the risk
1070of using an experimental feature which may change or be removed in a
1071future Perl version:
1072
1073 no warnings "experimental::lexical_subs";
1074 use feature "lexical_subs";
1075
1076=item *
1077
1078L<sleep(%u) too large|perldiag/"sleep(%u) too large">
1079
1080(W overflow) You called C<sleep> with a number that was larger than it can
1081reliably handle and C<sleep> probably slept for less time than requested.
1082
1083=item *
1084
1085L<Wide character in setenv|perldiag/"Wide character in %s">
1086
1087Attempts to put wide characters into environment variables via C<%ENV> now
1088provoke this warning.
1089
1090=item *
1091
1092"L<Invalid negative number (%s) in chr|perldiag/"Invalid negative number (%s) in chr">"
1093
1094C<chr()> now warns when passed a negative value [perl #83048].
1095
1096=item *
1097
1098"L<Integer overflow in srand|perldiag/"Integer overflow in srand">"
1099
1100C<srand()> now warns when passed a value that doesn't fit in a C<UV> (since the
1101value will be truncated rather than overflowing) [perl #40605].
1102
1103=item *
1104
1105"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">"
1106
1107Running perl with the C<-i> flag now warns if no input files are provided on
1108the command line [perl #113410].
1109
1110=back
1111
1112=head2 Changes to Existing Diagnostics
1113
1114=over 4
1115
1116=item *
1117
1118L<$* is no longer supported|perldiag/"$* is no longer supported">
1119
1120The warning that use of C<$*> and C<$#> is no longer supported is now
1121generated for every location that references them. Previously it would fail
1122to be generated if another variable using the same typeglob was seen first
1123(e.g. C<@*> before C<$*>), and would not be generated for the second and
1124subsequent uses. (It's hard to fix the failure to generate warnings at all
1125without also generating them every time, and warning every time is
1126consistent with the warnings that C<$[> used to generate.)
1127
1128=item *
1129
1130The warnings for C<\b{> and C<\B{> were added. They are a deprecation
1131warning which should be turned off by that category. One should not
1132have to turn off regular regexp warnings as well to get rid of these.
1133
1134=item *
1135
1136L<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>
1137
1138Constant overloading that returns C<undef> results in this error message.
1139For numeric constants, it used to say "Constant(undef)". "undef" has been
1140replaced with the number itself.
1141
1142=item *
1143
1144The error produced when a module cannot be loaded now includes a hint that
1145the module may need to be installed: "Can't locate hopping.pm in @INC (you
1146may need to install the hopping module) (@INC contains: ...)"
1147
1148=item *
1149
1150L<vector argument not supported with alpha versions|perldiag/vector argument not supported with alpha versions>
1151
1152This warning was not suppressable, even with C<no warnings>. Now it is
1153suppressible, and has been moved from the "internal" category to the
1154"printf" category.
1155
1156=item *
1157
1158C<< Can't do {n,m} with n > m in regex; marked by <-- HERE in m/%s/ >>
1159
1160This fatal error has been turned into a warning that reads:
1161
1162L<< Quantifier {n,m} with n > m can't match in regex | perldiag/Quantifier {n,m} with n > m can't match in regex >>
1163
1164(W regexp) Minima should be less than or equal to maxima. If you really want
1165your regexp to match something 0 times, just put {0}.
1166
1167=item *
1168
1169The "Runaway prototype" warning that occurs in bizarre cases has been
1170removed as being unhelpful and inconsistent.
1171
1172=item *
1173
1174The "Not a format reference" error has been removed, as the only case in
1175which it could be triggered was a bug.
1176
1177=item *
1178
1179The "Unable to create sub named %s" error has been removed for the same
1180reason.
1181
1182=item *
1183
1184The 'Can't use "my %s" in sort comparison' error has been downgraded to a
1185warning, '"my %s" used in sort comparison' (with 'state' instead of 'my'
1186for state variables). In addition, the heuristics for guessing whether
1187lexical $a or $b has been misused have been improved to generate fewer
1188false positives. Lexical $a and $b are no longer disallowed if they are
1189outside the sort block. Also, a named unary or list operator inside the
1190sort block no longer causes the $a or $b to be ignored [perl #86136].
1191
1192=back
1193
1194=head1 Utility Changes
1195
1196=head3 L<h2xs>
1197
1198=over 4
1199
1200=item *
1201
1202F<h2xs> no longer produces invalid code for empty defines. [perl #20636]
1203
1204=back
1205
1206=head1 Configuration and Compilation
1207
1208=over 4
1209
1210=item *
1211
1212Added C<useversionedarchname> option to Configure
1213
1214When set, it includes 'api_versionstring' in 'archname'. E.g.
1215x86_64-linux-5.13.6-thread-multi. It is unset by default.
1216
1217This feature was requested by Tim Bunce, who observed that
1218INSTALL_BASE creates a library structure that does not
1219differentiate by perl version. Instead, it places architecture
1220specific files in "$install_base/lib/perl5/$archname". This makes
1221it difficult to use a common INSTALL_BASE library path with
1222multiple versions of perl.
1223
1224By setting -Duseversionedarchname, the $archname will be
c2959982 1225distinct for architecture I<and> API version, allowing mixed use of
5ed58cbd
RS
1226INSTALL_BASE.
1227
1228=item *
1229
ff772877
RS
1230Add a C<PERL_NO_INLINE_FUNCTIONS> option
1231
1232If PERL_NO_INLINE_FUNCTIONS is defined, don't include "inline.h"
1233
1234This permits test code to include the perl headers for definitions without
1235creating a link dependency on the perl library (which may not exist yet).
1236
1237=item *
1238
5ed58cbd
RS
1239Configure will honour the external C<MAILDOMAIN> environment variable, if set.
1240
1241=item *
1242
1243C<installman> no longer ignores the silent option
1244
1245=item *
1246
1247Both C<META.yml> and C<META.json> files are now included in the distribution.
1248
1249=item *
1250
1251F<Configure> will now correctly detect C<isblank()> when compiling with a C++
1252compiler.
1253
1254=item *
1255
1256The pager detection in F<Configure> has been improved to allow responses which
1257specify options after the program name, e.g. B</usr/bin/less -R>, if the user
1258accepts the default value. This helps B<perldoc> when handling ANSI escapes
1259[perl #72156].
1260
1261=back
1262
1263=head1 Testing
1264
1265=over 4
1266
1267=item *
1268
1269The test suite now has a section for tests that require very large amounts
1270of memory. These tests won't run by default; they can be enabled by
1271setting the C<PERL_TEST_MEMORY> environment variable to the number of
1272gibibytes of memory that may be safely used.
1273
1274=back
1275
1276=head1 Platform Support
1277
1278=head2 Discontinued Platforms
1279
1280=over 4
1281
1282=item BeOS
1283
1284BeOS was an operating system for personal computers developed by Be Inc,
1285initially for their BeBox hardware. The OS Haiku was written as an open
1286source replacement for/continuation of BeOS, and its perl port is current and
1287actively maintained.
1288
1289=item UTS Global
1290
1291Support code relating to UTS global has been removed. UTS was a mainframe
1292version of System V created by Amdahl, subsequently sold to UTS Global. The
1293port has not been touched since before Perl 5.8.0, and UTS Global is now
1294defunct.
1295
1296=item VM/ESA
1297
1298Support for VM/ESA has been removed. The port was tested on 2.3.0, which
1299IBM ended service on in March 2002. 2.4.0 ended service in June 2003, and
1300was superseded by Z/VM. The current version of Z/VM is V6.2.0, and scheduled
1301for end of service on 2015/04/30.
1302
1303=item MPE/IX
1304
1305Support for MPE/IX has been removed.
1306
1307=item EPOC
1308
1309Support code relating to EPOC has been removed. EPOC was a family of
1310operating systems developed by Psion for mobile devices. It was the
1311predecessor of Symbian. The port was last updated in April 2002.
1312
1313=item Rhapsody
1314
1315Support for Rhapsody has been removed.
1316
1317=back
1318
1319=head2 Platform-Specific Notes
1320
1321=head3 AIX
1322
1323Configure now always adds C<-qlanglvl=extc99> to the CC flags on AIX when
1324using xlC. This will make it easier to compile a number of XS-based modules
1325that assume C99 [perl #113778].
1326
1327=head3 clang++
1328
1329There is now a workaround for a compiler bug that prevented compiling
1330with clang++ since Perl 5.15.7 [perl #112786].
1331
1332=head3 C++
1333
1334When compiling the Perl core as C++ (which is only semi-supported), the
1335mathom functions are now compiled as C<extern "C">, to ensure proper
1336binary compatibility. (However, binary compatibility isn't generally
1337guaranteed anyway in the situations where this would matter.)
1338
1339=head3 Darwin
1340
1341Stop hardcoding an alignment on 8 byte boundaries to fix builds using
1342-Dusemorebits.
1343
1344=head3 Haiku
1345
1346Perl should now work out of the box on Haiku R1 Alpha 4.
1347
1348=head3 MidnightBSD
1349
1350C<libc_r> was removed from recent versions of MidnightBSD and older versions
1351work better with C<pthread>. Threading is now enabled using C<pthread> which
1352corrects build errors with threading enabled on 0.4-CURRENT.
1353
1354=head3 Solaris
1355
1356In Configure, avoid running sed commands with flags not supported on Solaris.
1357
1358=head3 VMS
1359
1360=over
1361
1362=item *
1363
1364Where possible, the case of filenames and command-line arguments is now
1365preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
1366C<DECC$ARGV_PARSE_STYLE> at start-up time. The latter only takes effect
1367when extended parse is enabled in the process from which Perl is run.
1368
1369=item *
1370
1371The character set for Extended Filename Syntax (EFS) is now enabled by default
1372on VMS. Among other things, this provides better handling of dots in directory
1373names, multiple dots in filenames,and spaces in filenames. To obtain the old
1374behavior, set the logical name C<DECC$EFS_CHARSET> to C<DISABLE>.
1375
1376=item *
1377
1378Fix linking on builds configured with -Dusemymalloc=y.
1379
1380=item *
1381
1382It should now be possible to compile Perl as C++ on VMS.
1383
1384=item *
1385
1386All C header files from the top-level directory of the distribution are now
1387installed on VMS, providing consistency with a long-standing practice on other
1388platforms. Previously only a subset were installed, which broke non-core
1389extension builds for extensions that depended on the missing include files.
1390
1391=item *
1392
1393Quotes are now removed from the command verb (but not the parameters) for
1394commands spawned via C<system>, backticks, or a piped C<open>. Previously,
1395quotes on the verb were passed through to DCL, which would fail to recognize
1396the command. Also, if the verb is actually a path to an image or command
1397procedure on an ODS-5 volume, quoting it now allows the path to contain spaces.
1398
1399=item *
1400
1401The B<a2p> build has been fixed for the HP C++ compiler on OpenVMS.
1402
1403=back
1404
1405=head3 Win32
1406
1407=over
1408
1409=item *
1410
1411Perl can now be built using Microsoft's Visual C++ 2012 compiler by specifying
1412CCTYPE=MSVC110 (or MSVC110FREE if you are using the free Express edition for
1413Windows Desktop) in F<win32/Makefile>.
1414
1415=item *
1416
1417The option to build without USE_SOCKETS_AS_HANDLES has been removed.
1418
1419=item *
1420
1421Fixed a problem where perl could crash while cleaning up threads (including the
1422main thread) in threaded debugging builds on Win32 and possibly other platforms
1423[perl #114496].
1424
1425=item *
1426
1427A rare race condition that would lead to L<sleep|perlfunc/sleep> taking more
1428time than requested, and possibly even hanging, has been fixed [perl #33096].
1429
1430=item *
1431
1432C<link> on Win32 now attempts to set C<$!> to more appropriate values
1433based on the Win32 API error code. [perl #112272]
1434
1435Perl no longer mangles the environment block, e.g. when launching a new
1436sub-process, when the environment contains non-ASCII characters. Known
1437problems still remain, however, when the environment contains characters
1438outside of the current ANSI codepage (e.g. see the item about Unicode in
1439C<%ENV> in L<http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod>).
1440[perl #113536]
1441
1442=item *
1443
1444Building perl with some Windows compilers used to fail due to a problem
1445with miniperl's C<glob> operator (which uses the C<perlglob> program)
1446deleting the PATH environment variable [perl #113798].
1447
1448=item *
1449
1450A new makefile option, USE_64_BIT_INT, has been added to the Windows
1451makefiles. Set this to "define" when building a 32-bit perl if you want
1452it to use 64-bit integers.
1453
1454Machine code size reductions, already made to the DLLs of XS modules in
1455Perl 5.17.2, have now been extended to the perl DLL itself.
1456
1457Building with VC++ 6.0 was inadvertently broken in Perl 5.17.2 but has
1458now been fixed again.
1459
1460=back
1461
1462=head3 WinCE
1463
1464Building on WinCE is now possible once again, although more work is required
1465to fully restore a clean build.
1466
1467=head1 Internal Changes
1468
1469=over
1470
1471=item *
1472
4263dd11 1473Synonyms for the misleadingly named C<av_len()> have been created:
5ed58cbd
RS
1474C<av_top_index()> and C<av_tindex>. All three of these return the
1475number of the highest index in the array, not the number of elements it
1476contains.
1477
1478=item *
1479
1480SvUPGRADE() is no longer an expression. Originally this macro (and its
1481underlying function, sv_upgrade()) were documented as boolean, although
1482in reality they always croaked on error and never returned false. In 2005
1483the documentation was updated to specify a void return value, but
1484SvUPGRADE() was left always returning 1 for backwards compatibility. This
1485has now been removed, and SvUPGRADE() is now a statement with no return
1486value.
1487
1488So this is now a syntax error:
1489
1490 if (!SvUPGRADE(sv)) { croak(...); }
1491
1492If you have code like that, simply replace it with
1493
1494 SvUPGRADE(sv);
1495
1496or to to avoid compiler warnings with older perls, possibly
1497
1498 (void)SvUPGRADE(sv);
1499
1500=item *
1501
1502Perl has a new copy-on-write mechanism that allows any SvPOK scalar to be
1503upgraded to a copy-on-write scalar. A reference count on the string buffer
1504is stored in the string buffer itself.
1505
1506This breaks a few XS modules by allowing copy-on-write scalars to go
1507through code paths that never encountered them before.
1508
1509This behaviour can still be disabled by running F<Configure> with
1510B<-Accflags=-DPERL_NO_COW>. This option will probably be removed in Perl
15115.20.
1512
1513=item *
1514
1515Copy-on-write no longer uses the SvFAKE and SvREADONLY flags. Hence,
1516SvREADONLY indicates a true read-only SV.
1517
1518Use the SvIsCOW macro (as before) to identify a copy-on-write scalar.
1519
1520=item *
1521
1522PL_glob_index is gone.
1523
1524=item *
1525
1526The private Perl_croak_no_modify has had its context parameter removed. It is
1527now has a void prototype. Users of the public API croak_no_modify remain
1528unaffected.
1529
1530=item *
1531
1532Copy-on-write (shared hash key) scalars are no longer marked read-only.
1533C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
1534true.
1535
1536=item *
1537
1538A new op type, C<OP_PADRANGE> has been introduced. The perl peephole
1539optimiser will, where possible, substitute a single padrange op for a
1540pushmark followed by one or more pad ops, and possibly also skipping list
1541and nextstate ops. In addition, the op can carry out the tasks associated
1542with the RHS of a my(...) = @_ assignment, so those ops may be optimised
1543away too.
1544
1545=item *
1546
1547Case-insensitive matching inside a [bracketed] character class with a
1548multi-character fold no longer excludes one of the possibilities in the
1549circumstances that it used to. [perl #89774].
1550
1551=item *
1552
1553C<PL_formfeed> has been removed.
1554
1555=item *
1556
1557The regular expression engine no longer reads one byte past the end of the
1558target string. While for all internally well-formed scalars this should
1559never have been a problem, this change facilitates clever tricks with
1560string buffers in CPAN modules. [perl #73542]
1561
1562=item *
1563
1564Inside a BEGIN block, C<PL_compcv> now points to the currently-compiling
1565subroutine, rather than the BEGIN block itself.
1566
1567=item *
1568
1569C<mg_length> has been deprecated.
1570
1571=item *
1572
1573C<sv_len> now always returns a byte count and C<sv_len_utf8> a character
1574count. Previously, C<sv_len> and C<sv_len_utf8> were both buggy and would
1575sometimes returns bytes and sometimes characters. C<sv_len_utf8> no longer
1576assumes that its argument is in UTF8. Neither of these creates UTF8 caches
1577for tied or overloaded values or for non-PVs any more.
1578
1579=item *
1580
1581C<sv_mortalcopy> now copies string buffers of shared hash key scalars when
1582called from XS modules [perl #79824].
1583
1584=item *
1585
1586C<RXf_SPLIT> and C<RXf_SKIPWHITE> are no longer used. They are now
1587#defined as 0.
1588
1589=item *
1590
1591The new C<RXf_MODIFIES_VARS> flag can be set by custom regular expression
1592engines to indicate that the execution of the regular expression may cause
1593variables to be modified. This lets C<s///> know to skip certain
1594optimisations. Perl's own regular expression engine sets this flag for the
1595special backtracking verbs that set $REGMARK and $REGERROR.
1596
1597=item *
1598
1599The APIs for accessing lexical pads have changed considerably.
1600
1601C<PADLIST>s are now longer C<AV>s, but their own type instead.
1602C<PADLIST>s now contain a C<PAD> and a C<PADNAMELIST> of C<PADNAME>s,
1603rather than C<AV>s for the pad and the list of pad names. C<PAD>s,
1604C<PADNAMELIST>s, and C<PADNAME>s are to be accessed as such through the
1605newly added pad API instead of the plain C<AV> and C<SV> APIs. See
1606L<perlapi> for details.
1607
1608=item *
1609
1610In the regex API, the numbered capture callbacks are passed an index
1611indicating what match variable is being accessed. There are special
1612index values for the C<$`, $&, $&> variables. Previously the same three
1613values were used to retrieve C<${^PREMATCH}, ${^MATCH}, ${^POSTMATCH}>
1614too, but these have now been assigned three separate values. See
1615L<perlreapi/Numbered capture callbacks>.
1616
1617=item *
1618
1619C<PL_sawampersand> was previously a boolean indicating that any of
1620C<$`, $&, $&> had been seen; it now contains three one-bit flags
1621indicating the presence of each of the variables individually.
1622
1623=item *
1624
1625The C<CV *> typemap entry now supports C<&{}> overloading and typeglobs,
1626just like C<&{...}> [perl #96872].
1627
1628=item *
1629
1630The C<SVf_AMAGIC> flag to indicate overloading is now on the stash, not the
1631object. It is now set automatically whenever a method or @ISA changes, so
1632its meaning has changed, too. It now means "potentially overloaded". When
1633the overload table is calculated, the flag is automatically turned off if
1634there is no overloading, so there should be no noticeable slowdown.
1635
1636The staleness of the overload tables is now checked when overload methods
1637are invoked, rather than during C<bless>.
1638
1639"A" magic is gone. The changes to the handling of the C<SVf_AMAGIC> flag
1640eliminate the need for it.
1641
1642C<PL_amagic_generation> has been removed as no longer necessary. For XS
1643modules, it is now a macro alias to C<PL_na>.
1644
1645The fallback overload setting is now stored in a stash entry separate from
1646overloadedness itself.
1647
1648=item *
1649
1650The character-processing code has been cleaned up in places. The changes
1651should be operationally invisible.
1652
1653=item *
1654
1655The C<study> function was made a no-op in 5.16. It was simply disabled via
1656a C<return> statement; the code was left in place. Now the code supporting
1657what C<study> used to do has been removed.
1658
1659=item *
1660
1661Under threaded perls, there is no longer a separate PV allocated for every
1662COP to store its package name (C<< cop->stashpv >>). Instead, there is an
1663offset (C<< cop->stashoff >>) into the new C<PL_stashpad> array, which
1664holds stash pointers.
1665
1666=item *
1667
1668In the pluggable regex API, the C<regexp_engine> struct has acquired a new
1669field C<op_comp>, which is currently just for perl's internal use, and
1670should be initialised to NULL by other regex plugin modules.
1671
1672=item *
1673
1674A new function C<alloccoptash> has been added to the API, but is considered
1675experimental. See L<perlapi>.
1676
1677=item *
1678
1679Perl used to implement get magic in a way that would sometimes hide bugs in
4263dd11 1680code that could call mg_get() too many times on magical values. This hiding of
5ed58cbd
RS
1681errors no longer occurs, so long-standing bugs may become visible now. If
1682you see magic-related errors in XS code, check to make sure it, together
1683with the Perl API functions it uses, calls mg_get() only once on SvGMAGICAL()
1684values.
1685
1686=item *
1687
1688OP allocation for CVs now uses a slab allocator. This simplifies
1689memory management for OPs allocated to a CV, so cleaning up after a
1690compilation error is simpler and safer [perl #111462][perl #112312].
1691
1692=item *
1693
1694PERL_DEBUG_READONLY_OPS has been rewritten to work with the new slab
1695allocator, allowing it to catch more violations than before.
1696
1697=item *
1698
1699The old slab allocator for ops, which was only enabled for PERL_IMPLICIT_SYS
1700and PERL_DEBUG_READONLY_OPS, has been retired.
1701
1702=back
1703
1704=head1 Selected Bug Fixes
1705
1706=over 4
1707
1708=item *
1709
1710Here-doc terminators no longer require a terminating newline character when
1711they occur at the end of a file. This was already the case at the end of a
1712string eval [perl #65838].
1713
1714=item *
1715
1716-DPERL_GLOBAL_STRUCT builds now free the global struct B<after>
1717they've finished using it.
1718
1719=item *
1720
1721A trailing '/' on a path in @INC will no longer have an additional '/'
1722appended.
1723
1724=item *
1725
1726The C<:crlf> layer now works when unread data doesn't fit into its own
1727buffer. [perl #112244].
1728
1729=item *
1730
1731C<ungetc()> now handles UTF-8 encoded data. [perl #116322].
1732
1733=item *
1734
1735A bug in the core typemap caused any C types that map to the T_BOOL core
1736typemap entry to not be set, updated, or modified when the T_BOOL variable was
1737used in an OUTPUT: section with an exception for RETVAL. T_BOOL in an INPUT:
1738section was not affected. Using a T_BOOL return type for an XSUB (RETVAL)
1739was not affected. A side effect of fixing this bug is, if a T_BOOL is specified
1740in the OUTPUT: section (which previous did nothing to the SV), and a read only
1741SV (literal) is passed to the XSUB, croaks like "Modification of a read-only
1742value attempted" will happen. [perl #115796]
1743
1744=item *
1745
1746On many platforms, providing a directory name as the script name caused perl
1747to do nothing and report success. It should now universally report an error
1748and exit nonzero. [perl #61362]
1749
1750=item *
1751
1752C<sort {undef} ...> under fatal warnings no longer crashes. It had
1753begun crashing in Perl 5.16.
1754
1755=item *
1756
1757Stashes blessed into each other
1758(C<bless \%Foo::, 'Bar'; bless \%Bar::, 'Foo'>) no longer result in double
1759frees. This bug started happening in Perl 5.16.
1760
1761=item *
1762
1763Numerous memory leaks have been fixed, mostly involving fatal warnings and
1764syntax errors.
1765
1766=item *
1767
1768Some failed regular expression matches such as C<'f' =~ /../g> were not
1769resetting C<pos>. Also, "match-once" patterns (C<m?...?g>) failed to reset
1770it, too, when invoked a second time [perl #23180].
1771
1772=item *
1773
1774Accessing C<$&> after a pattern match now works if it had not been seen
1775before the match. I.e., this applies to C<${'&'}> (under C<no strict>) and
1776C<eval '$&'>. The same applies to C<$'> and C<$`> [perl #4289].
1777
1778=item *
1779
1780Several bugs involving C<local *ISA> and C<local *Foo::> causing stale
1781MRO caches have been fixed.
1782
1783=item *
1784
1785Defining a subroutine when its typeglob has been aliased no longer results
1786in stale method caches. This bug was introduced in Perl 5.10.
1787
1788=item *
1789
1790Localising a typeglob containing a subroutine when the typeglob's package
1791has been deleted from its parent stash no longer produces an error. This
1792bug was introduced in Perl 5.14.
1793
1794=item *
1795
1796Under some circumstances, C<local *method=...> would fail to reset method
1797caches upon scope exit.
1798
1799=item *
1800
1801C</[.foo.]/> is no longer an error, but produces a warning (as before) and
1802is treated as C</[.fo]/> [perl #115818].
1803
1804=item *
1805
1806C<goto $tied_var> now calls FETCH before deciding what type of goto
1807(subroutine or label) this is.
1808
1809=item *
1810
1811Renaming packages through glob assignment
1812(C<*Foo:: = *Bar::; *Bar:: = *Baz::>) in combination with C<m?...?> and
1813C<reset> no longer makes threaded builds crash.
1814
1815=item *
1816
1817A number of bugs related to assigning a list to hash have been fixed. Many of
1818these involve lists with repeated keys like C<(1, 1, 1, 1)>.
1819
1820=over 4
1821
1822=item *
1823
1824The expression C<scalar(%h = (1, 1, 1, 1))> now returns C<4>, not C<2>.
1825
1826=item *
1827
1828The return value of C<%h = (1, 1, 1)> in list context was wrong. Previously
1829this would return C<(1, undef, 1)>, now it returns C<(1, undef)>.
1830
1831=item *
1832
1833Perl now issues the same warning on C<($s, %h) = (1, {})> as it does for
1834C<(%h) = ({})>, "Reference found where even-sized list expected".
1835
1836=item *
1837
1838A number of additional edge cases in list assignment to hashes were
1839corrected. For more details see commit 23b7025ebc.
1840
1841=back
1842
1843=item *
1844
1845Attributes applied to lexical variables no longer leak memory.
1846[perl #114764]
1847
1848=item *
1849
1850C<dump>, C<goto>, C<last>, C<next>, C<redo> or C<require> followed by a
1851bareword (or version) and then an infix operator is no longer a syntax
1852error. It used to be for those infix operators (like C<+>) that have a
1853different meaning where a term is expected. [perl #105924]
1854
1855=item *
1856
1857C<require a::b . 1> and C<require a::b + 1> no longer produce erroneous
1858ambiguity warnings. [perl #107002]
1859
1860=item *
1861
1862Class method calls are now allowed on any string, and not just strings
1863beginning with an alphanumeric character. [perl #105922]
1864
1865=item *
1866
1867An empty pattern created with C<qr//> used in C<m///> no longer triggers
1868the "empty pattern reuses last pattern" behaviour. [perl #96230]
1869
1870=item *
1871
1872Tying a hash during iteration no longer results in a memory leak.
1873
1874=item *
1875
1876Freeing a tied hash during iteration no longer results in a memory leak.
1877
1878=item *
1879
1880List assignment to a tied array or hash that dies on STORE no longer
1881results in a memory leak.
1882
1883=item *
1884
1885If the hint hash (C<%^H>) is tied, compile-time scope entry (which copies
1886the hint hash) no longer leaks memory if FETCH dies. [perl #107000]
1887
1888=item *
1889
1890Constant folding no longer inappropriately triggers the special
1891C<split " "> behaviour. [perl #94490]
1892
1893=item *
1894
1895C<defined scalar(@array)>, C<defined do { &foo }>, and similar constructs
1896now treat the argument to C<defined> as a simple scalar. [perl #97466]
1897
1898=item *
1899
1900Running a custom debugging that defines no C<*DB::DB> glob or provides a
1901subroutine stub for C<&DB::DB> no longer results in a crash, but an error
1902instead. [perl #114990]
1903
1904=item *
1905
1906C<reset ""> now matches its documentation. C<reset> only resets C<m?...?>
1907patterns when called with no argument. An empty string for an argument now
1908does nothing. (It used to be treated as no argument.) [perl #97958]
1909
1910=item *
1911
1912C<printf> with an argument returning an empty list no longer reads past the
1913end of the stack, resulting in erratic behaviour. [perl #77094]
1914
1915=item *
1916
1917C<--subname> no longer produces erroneous ambiguity warnings.
1918[perl #77240]
1919
1920=item *
1921
1922C<v10> is now allowed as a label or package name. This was inadvertently
1923broken when v-strings were added in Perl 5.6. [perl #56880]
1924
1925=item *
1926
1927C<length>, C<pos>, C<substr> and C<sprintf> could be confused by ties,
1928overloading, references and typeglobs if the stringification of such
1929changed the internal representation to or from UTF8. [perl #114410]
1930
1931=item *
1932
1933utf8::encode now calls FETCH and STORE on tied variables. utf8::decode now
1934calls STORE (it was already calling FETCH).
1935
1936=item *
1937
1938C<$tied =~ s/$non_utf8/$utf8/> no longer loops infinitely if the tied
1939variable returns a Latin-1 string, shared hash key scalar, or reference or
2ae351f8 1940typeglob that stringifies as ASCII or Latin-1. This was a regression from
5ed58cbd
RS
19415.12.x.
1942
1943=item *
1944
1945C<s///> without /e is now better at detecting when it needs to forego
1946certain optimisations, fixing some buggy cases:
1947
1948=over
1949
1950=item *
1951
1952Match variables in certain constructs (C<&&>, C<||>, C<..> and others) in
1953the replacement part; e.g., C<s/(.)/$l{$a||$1}/g>. [perl #26986]
1954
1955=item *
1956
1957Aliases to match variables in the replacement.
1958
1959=item *
1960
1961C<$REGERROR> or C<$REGMARK> in the replacement. [perl #49190]
1962
1963=item *
1964
1965An empty pattern (C<s//$foo/>) that causes the last-successful pattern to
1966be used, when that pattern contains code blocks that modify the variables
1967in the replacement.
1968
1969=back
1970
1971=item *
1972
1973The taintedness of the replacement string no longer affects the taintedness
1974of the return value of C<s///e>.
1975
1976=item *
1977
1978The C<$|> autoflush variable is created on-the-fly when needed. If this
1979happened (e.g., if it was mentioned in a module or eval) when the
1980currently-selected filehandle was a typeglob with an empty IO slot, it used
1981to crash. [perl #115206]
1982
1983=item *
1984
1985Line numbers at the end of a string eval are no longer off by one.
1986[perl #114658]
1987
1988=item *
1989
1990@INC filters (subroutines returned by subroutines in @INC) that set $_ to a
1991copy-on-write scalar no longer cause the parser to modify that string
1992buffer in place.
1993
1994=item *
1995
1996C<length($object)> no longer returns the undefined value if the object has
1997string overloading that returns undef. [perl #115260]
1998
1999=item *
2000
2001The use of C<PL_stashcache>, the stash name lookup cache for method calls, has
2002been restored,
2003
2004Commit da6b625f78f5f133 in August 2011 inadvertently broke the code that looks
2005up values in C<PL_stashcache>. As it's a only cache, quite correctly everything
2006carried on working without it.
2007
2008=item *
2009
2010The error "Can't localize through a reference" had disappeared in 5.16.0
2011when C<local %$ref> appeared on the last line of an lvalue subroutine.
2012This error disappeared for C<\local %$ref> in perl 5.8.1. It has now
2013been restored.
2014
2015=item *
2016
2017The parsing of here-docs has been improved significantly, fixing several
2018parsing bugs and crashes and one memory leak, and correcting wrong
2019subsequent line numbers under certain conditions.
2020
2021=item *
2022
2023Inside an eval, the error message for an unterminated here-doc no longer
2024has a newline in the middle of it [perl #70836].
2025
2026=item *
2027
2028A substitution inside a substitution pattern (C<s/${s|||}//>) no longer
2029confuses the parser.
2030
2031=item *
2032
2033It may be an odd place to allow comments, but C<s//"" # hello/e> has
2034always worked, I<unless> there happens to be a null character before the
2035first #. Now it works even in the presence of nulls.
2036
2037=item *
2038
2039An invalid range in C<tr///> or C<y///> no longer results in a memory leak.
2040
2041=item *
2042
2043String eval no longer treats a semicolon-delimited quote-like operator at
2044the very end (C<eval 'q;;'>) as a syntax error.
2045
2046=item *
2047
2048C<< warn {$_ => 1} + 1 >> is no longer a syntax error. The parser used to
2049get confused with certain list operators followed by an anonymous hash and
2050then an infix operator that shares its form with a unary operator.
2051
2052=item *
2053
2054C<(caller $n)[6]> (which gives the text of the eval) used to return the
2055actual parser buffer. Modifying it could result in crashes. Now it always
2056returns a copy. The string returned no longer has "\n;" tacked on to the
2057end. The returned text also includes here-doc bodies, which used to be
2058omitted.
2059
2060=item *
2061
2062Reset the utf8 position cache when accessing magical variables to avoid the
2063string buffer and the utf8 position cache getting out of sync
2064[perl #114410].
2065
2066=item *
2067
2068Various cases of get magic being called twice for magical utf8 strings have been
2069fixed.
2070
2071=item *
2072
2073This code (when not in the presence of C<$&> etc)
2074
2075 $_ = 'x' x 1_000_000;
2076 1 while /(.)/;
2077
2078used to skip the buffer copy for performance reasons, but suffered from C<$1>
2079etc changing if the original string changed. That's now been fixed.
2080
2081=item *
2082
2083Perl doesn't use PerlIO anymore to report out of memory messages, as PerlIO
2084might attempt to allocate more memory.
2085
2086=item *
2087
2088In a regular expression, if something is quantified with C<{n,m}> where
2089C<S<n E<gt> m>>, it can't possibly match. Previously this was a fatal
2090error, but now is merely a warning (and that something won't match).
2091[perl #82954].
2092
2093=item *
2094
2095It used to be possible for formats defined in subroutines that have
2096subsequently been undefined and redefined to close over variables in the
2097wrong pad (the newly-defined enclosing sub), resulting in crashes or
2098"Bizarre copy" errors.
2099
2100=item *
2101
2102Redefinition of XSUBs at run time could produce warnings with the wrong
2103line number.
2104
2105=item *
2106
2107The %vd sprintf format does not support version objects for alpha versions.
2108It used to output the format itself (%vd) when passed an alpha version, and
2109also emit an "Invalid conversion in printf" warning. It no longer does,
2110but produces the empty string in the output. It also no longer leaks
2111memory in this case.
2112
2113=item *
2114
2115C<< $obj->SUPER::method >> calls in the main package could fail if the
2116SUPER package had already been accessed by other means.
2117
2118=item *
2119
2120Stash aliasing (C<*foo:: = *bar::>) no longer causes SUPER calls to ignore
2121changes to methods or @ISA or use the wrong package.
2122
2123=item *
2124
2125Method calls on packages whose names end in ::SUPER are no longer treated
2126as SUPER method calls, resulting in failure to find the method.
2127Furthermore, defining subroutines in such packages no longer causes them to
2128be found by SUPER method calls on the containing package [perl #114924].
2129
2130=item *
2131
2132C<\w> now matches the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D
2133(ZERO WIDTH JOINER). C<\W> no longer matches these. This change is because
2134Unicode corrected their definition of what C<\w> should match.
2135
2136=item *
2137
2138C<dump LABEL> no longer leaks its label.
2139
2140=item *
2141
2142Constant folding no longer changes the behaviour of functions like C<stat()>
2143and C<truncate()> that can take either filenames or handles.
2144C<stat 1 ? foo : bar> nows treats its argument as a file name (since it is an
2145arbitrary expression), rather than the handle "foo".
2146
2147=item *
2148
2149C<truncate FOO, $len> no longer falls back to treating "FOO" as a file name if
2150the filehandle has been deleted. This was broken in Perl 5.16.0.
2151
2152=item *
2153
2154Subroutine redefinitions after sub-to-glob and glob-to-glob assignments no
2155longer cause double frees or panic messages.
2156
2157=item *
2158
2159C<s///> now turns vstrings into plain strings when performing a substitution,
2160even if the resulting string is the same (C<s/a/a/>).
2161
2162=item *
2163
2164Prototype mismatch warnings no longer erroneously treat constant subs as having
2165no prototype when they actually have "".
2166
2167=item *
2168
2169Constant subroutines and forward declarations no longer prevent prototype
2170mismatch warnings from omitting the sub name.
2171
2172=item *
2173
2174C<undef> on a subroutine now clears call checkers.
2175
2176=item *
2177
2178The C<ref> operator started leaking memory on blessed objects in Perl 5.16.0.
2179This has been fixed [perl #114340].
2180
2181=item *
2182
2183C<use> no longer tries to parse its arguments as a statement, making
2184C<use constant { () };> a syntax error [perl #114222].
2185
2186=item *
2187
2188On debugging builds, "uninitialized" warnings inside formats no longer cause
2189assertion failures.
2190
2191=item *
2192
2193On debugging builds, subroutines nested inside formats no longer cause
2194assertion failures [perl #78550].
2195
2196=item *
2197
2198Formats and C<use> statements are now permitted inside formats.
2199
2200=item *
2201
2202C<print $x> and C<sub { print $x }-E<gt>()> now always produce the same output.
2203It was possible for the latter to refuse to close over $x if the variable was
2204not active; e.g., if it was defined outside a currently-running named
2205subroutine.
2206
2207=item *
2208
2209Similarly, C<print $x> and C<print eval '$x'> now produce the same output.
2210This also allows "my $x if 0" variables to be seen in the debugger [perl
2211#114018].
2212
2213=item *
2214
2215Formats called recursively no longer stomp on their own lexical variables, but
2216each recursive call has its own set of lexicals.
2217
2218=item *
2219
2220Attempting to free an active format or the handle associated with it no longer
2221results in a crash.
2222
2223=item *
2224
2225Format parsing no longer gets confused by braces, semicolons and low-precedence
2226operators. It used to be possible to use braces as format delimiters (instead
2227of C<=> and C<.>), but only sometimes. Semicolons and low-precedence operators
2228in format argument lines no longer confuse the parser into ignoring the line's
2229return value. In format argument lines, braces can now be used for anonymous
2230hashes, instead of being treated always as C<do> blocks.
2231
2232=item *
2233
2234Formats can now be nested inside code blocks in regular expressions and other
2235quoted constructs (C</(?{...})/> and C<qq/${...}/>) [perl #114040].
2236
2237=item *
2238
2239Formats are no longer created after compilation errors.
2240
2241=item *
2242
2243Under debugging builds, the B<-DA> command line option started crashing in Perl
22445.16.0. It has been fixed [perl #114368].
2245
2246=item *
2247
2248A potential deadlock scenario involving the premature termination of a pseudo-
2249forked child in a Windows build with ithreads enabled has been fixed. This
2250resolves the common problem of the F<t/op/fork.t> test hanging on Windows [perl
2251#88840].
2252
2253=item *
2254
2255The microperl build, broken since Perl 5.15.7, has now been restored.
2256
2257=item *
2258
2259The code which generates errors from C<require()> could potentially read one or
2260two bytes before the start of the filename for filenames less than three bytes
2261long and ending C</\.p?\z/>. This has now been fixed. Note that it could
2262never have happened with module names given to C<use()> or C<require()> anyway.
2263
2264=item *
2265
2266The handling of pathnames of modules given to C<require()> has been made
2267thread-safe on VMS.
2268
2269=item *
2270
d85cd26b
RS
2271Non-blocking sockets have been fixed on VMS.
2272
2273=item *
2274
5ed58cbd
RS
2275A bug in the compilation of a C</(?{})/> expression which affected the TryCatch
2276test suite has been fixed [perl #114242].
2277
2278=item *
2279
2280Pod can now be nested in code inside a quoted construct outside of a string
2281eval. This used to work only within string evals [perl #114040].
2282
2283=item *
2284
2285C<goto ''> now looks for an empty label, producing the "goto must have
2286label" error message, instead of exiting the program [perl #111794].
2287
2288=item *
2289
2290C<goto "\0"> now dies with "Can't find label" instead of "goto must have
2291label".
2292
2293=item *
2294
2295The C function C<hv_store> used to result in crashes when used on C<%^H>
2296[perl #111000].
2297
2298=item *
2299
2300A call checker attached to a closure prototype via C<cv_set_call_checker>
2301is now copied to closures cloned from it. So C<cv_set_call_checker> now
2302works inside an attribute handler for a closure.
2303
2304=item *
2305
2306Writing to C<$^N> used to have no effect. Now it croaks with "Modification
2307of a read-only value" by default, but that can be overridden by a custom
2308regular expression engine, as with C<$1> [perl #112184].
2309
2310=item *
2311
2312C<undef> on a control character glob (C<undef *^H>) no longer emits an
2313erroneous warning about ambiguity [perl #112456].
2314
2315=item *
2316
2317For efficiency's sake, many operators and built-in functions return the
2318same scalar each time. Lvalue subroutines and subroutines in the CORE::
2319namespace were allowing this implementation detail to leak through.
2320C<print &CORE::uc("a"), &CORE::uc("b")> used to print "BB". The same thing
2321would happen with an lvalue subroutine returning the return value of C<uc>.
2322Now the value is copied in such cases.
2323
2324=item *
2325
2326C<method {}> syntax with an empty block or a block returning an empty list
2327used to crash or use some random value left on the stack as its invocant.
2328Now it produces an error.
2329
2330=item *
2331
2332C<vec> now works with extremely large offsets (E<gt>2 GB) [perl #111730].
2333
2334=item *
2335
2336Changes to overload settings now take effect immediately, as do changes to
2337inheritance that affect overloading. They used to take effect only after
2338C<bless>.
2339
2340Objects that were created before a class had any overloading used to remain
2341non-overloaded even if the class gained overloading through C<use overload>
2342or @ISA changes, and even after C<bless>. This has been fixed
2343[perl #112708].
2344
2345=item *
2346
2347Classes with overloading can now inherit fallback values.
2348
2349=item *
2350
2351Overloading was not respecting a fallback value of 0 if there were
2352overloaded objects on both sides of an assignment operator like C<+=>
2353[perl #111856].
2354
2355=item *
2356
2357C<pos> now croaks with hash and array arguments, instead of producing
2358erroneous warnings.
2359
2360=item *
2361
2362C<while(each %h)> now implies C<while(defined($_ = each %h))>, like
2363C<readline> and C<readdir>.
2364
2365=item *
2366
2367Subs in the CORE:: namespace no longer crash after C<undef *_> when called
2368with no argument list (C<&CORE::time> with no parentheses).
2369
2370=item *
2371
2372C<unpack> no longer produces the "'/' must follow a numeric type in unpack"
2373error when it is the data that are at fault [perl #60204].
2374
2375=item *
2376
2377C<join> and C<"@array"> now call FETCH only once on a tied C<$">
2378[perl #8931].
2379
2380=item *
2381
2382Some subroutine calls generated by compiling core ops affected by a
2383C<CORE::GLOBAL> override had op checking performed twice. The checking
2384is always idempotent for pure Perl code, but the double checking can
2385matter when custom call checkers are involved.
2386
2387=item *
2388
2389A race condition used to exist around fork that could cause a signal sent to
2390the parent to be handled by both parent and child. Signals are now blocked
2391briefly around fork to prevent this from happening [perl #82580].
2392
2393=item *
2394
2395The implementation of code blocks in regular expressions, such as C<(?{})>
2396and C<(??{})>, has been heavily reworked to eliminate a whole slew of bugs.
2397The main user-visible changes are:
2398
2399=over 4
2400
2401=item *
2402
2403Code blocks within patterns are now parsed in the same pass as the
2404surrounding code; in particular it is no longer necessary to have balanced
2405braces: this now works:
2406
2407 /(?{ $x='{' })/
2408
2409This means that this error message is no longer generated:
2410
2411 Sequence (?{...}) not terminated or not {}-balanced in regex
2412
2413but a new error may be seen:
2414
2415 Sequence (?{...}) not terminated with ')'
2416
2417In addition, literal code blocks within run-time patterns are only
2418compiled once, at perl compile-time:
2419
2420 for my $p (...) {
2421 # this 'FOO' block of code is compiled once,
2422 # at the same time as the surrounding 'for' loop
2423 /$p{(?{FOO;})/;
2424 }
2425
2426=item *
2427
2428Lexical variables are now sane as regards scope, recursion and closure
2429behavior. In particular, C</A(?{B})C/> behaves (from a closure viewpoint)
2430exactly like C</A/ && do { B } && /C/>, while C<qr/A(?{B})C/> is like
2431C<sub {/A/ && do { B } && /C/}>. So this code now works how you might
2432expect, creating three regexes that match 0, 1, and 2:
2433
2434 for my $i (0..2) {
2435 push @r, qr/^(??{$i})$/;
2436 }
2437 "1" =~ $r[1]; # matches
2438
2439=item *
2440
2441The C<use re 'eval'> pragma is now only required for code blocks defined
2442at runtime; in particular in the following, the text of the C<$r> pattern is
2443still interpolated into the new pattern and recompiled, but the individual
2444compiled code-blocks within C<$r> are reused rather than being recompiled,
2445and C<use re 'eval'> isn't needed any more:
2446
2447 my $r = qr/abc(?{....})def/;
2448 /xyz$r/;
2449
2450=item *
2451
2452Flow control operators no longer crash. Each code block runs in a new
2453dynamic scope, so C<next> etc. will not see
2454any enclosing loops. C<return> returns a value
2455from the code block, not from any enclosing subroutine.
2456
2457=item *
2458
2459Perl normally caches the compilation of run-time patterns, and doesn't
2460recompile if the pattern hasn't changed, but this is now disabled if
2461required for the correct behavior of closures. For example:
2462
2463 my $code = '(??{$x})';
2464 for my $x (1..3) {
2465 # recompile to see fresh value of $x each time
2466 $x =~ /$code/;
2467 }
2468
2469=item *
2470
2471The C</msix> and C<(?msix)> etc. flags are now propagated into the return
2472value from C<(??{})>; this now works:
2473
2474 "AB" =~ /a(??{'b'})/i;
2475
2476=item *
2477
2478Warnings and errors will appear to come from the surrounding code (or for
2479run-time code blocks, from an eval) rather than from an C<re_eval>:
2480
2481 use re 'eval'; $c = '(?{ warn "foo" })'; /$c/;
2482 /(?{ warn "foo" })/;
2483
2484formerly gave:
2485
2486 foo at (re_eval 1) line 1.
2487 foo at (re_eval 2) line 1.
2488
2489and now gives:
2490
2491 foo at (eval 1) line 1.
2492 foo at /some/prog line 2.
2493
2494=back
2495
2496=item *
2497
2e7bc647
KW
2498Perl now can be recompiled to use any Unicode version. In v5.16, it
2499worked on Unicodes 6.0 and 6.1, but there were various bugs if earlier
2500releases were used; the older the release the more problems.
5ed58cbd
RS
2501
2502=item *
2503
2504C<vec> no longer produces "uninitialized" warnings in lvalue context
2505[perl #9423].
2506
2507=item *
2508
2509An optimization involving fixed strings in regular expressions could cause
2510a severe performance penalty in edge cases. This has been fixed
2511[perl #76546].
2512
2513=item *
2514
2515In certain cases, including empty subpatterns within a regular expression (such
2516as C<(?:)> or C<(?:|)>) could disable some optimizations. This has been fixed.
2517
2518=item *
2519
2520The "Can't find an opnumber" message that C<prototype> produces when passed
2521a string like "CORE::nonexistent_keyword" now passes UTF-8 and embedded
2522NULs through unchanged [perl #97478].
2523
2524=item *
2525
2526C<prototype> now treats magical variables like C<$1> the same way as
2527non-magical variables when checking for the CORE:: prefix, instead of
2528treating them as subroutine names.
2529
2530=item *
2531
2532Under threaded perls, a runtime code block in a regular expression could
2533corrupt the package name stored in the op tree, resulting in bad reads
2534in C<caller>, and possibly crashes [perl #113060].
2535
2536=item *
2537
2538Referencing a closure prototype (C<\&{$_[1]}> in an attribute handler for a
2539closure) no longer results in a copy of the subroutine (or assertion
2540failures on debugging builds).
2541
2542=item *
2543
2544C<eval '__PACKAGE__'> now returns the right answer on threaded builds if
2545the current package has been assigned over (as in
2546C<*ThisPackage:: = *ThatPackage::>) [perl #78742].
2547
2548=item *
2549
2550If a package is deleted by code that it calls, it is possible for C<caller>
2551to see a stack frame belonging to that deleted package. C<caller> could
2552crash if the stash's memory address was reused for a scalar and a
2553substitution was performed on the same scalar [perl #113486].
2554
2555=item *
2556
2557C<UNIVERSAL::can> no longer treats its first argument differently
2558depending on whether it is a string or number internally.
2559
2560=item *
2561
2562C<open> with C<< <& >> for the mode checks to see whether the third argument is
2563a number, in determining whether to treat it as a file descriptor or a handle
2564name. Magical variables like C<$1> were always failing the numeric check and
2565being treated as handle names.
2566
2567=item *
2568
2569C<warn>'s handling of magical variables (C<$1>, ties) has undergone several
2570fixes. C<FETCH> is only called once now on a tied argument or a tied C<$@>
2571[perl #97480]. Tied variables returning objects that stringify as "" are
2572no longer ignored. A tied C<$@> that happened to return a reference the
2573I<previous> time it was used is no longer ignored.
2574
2575=item *
2576
2577C<warn ""> now treats C<$@> with a number in it the same way, regardless of
2578whether it happened via C<$@=3> or C<$@="3">. It used to ignore the
2579former. Now it appends "\t...caught", as it has always done with
2580C<$@="3">.
2581
2582=item *
2583
2584Numeric operators on magical variables (e.g., S<C<$1 + 1>>) used to use
2585floating point operations even where integer operations were more appropriate,
2586resulting in loss of accuracy on 64-bit platforms [perl #109542].
2587
2588=item *
2589
2590Unary negation no longer treats a string as a number if the string happened
2591to be used as a number at some point. So, if C<$x> contains the string "dogs",
2592C<-$x> returns "-dogs" even if C<$y=0+$x> has happened at some point.
2593
2594=item *
2595
2596In Perl 5.14, C<-'-10'> was fixed to return "10", not "+10". But magical
2597variables (C<$1>, ties) were not fixed till now [perl #57706].
2598
2599=item *
2600
2601Unary negation now treats strings consistently, regardless of the internal
2602C<UTF8> flag.
2603
2604=item *
2605
2606A regression introduced in Perl v5.16.0 involving
2607C<tr/I<SEARCHLIST>/I<REPLACEMENTLIST>/> has been fixed. Only the first
2608instance is supposed to be meaningful if a character appears more than
2609once in C<I<SEARCHLIST>>. Under some circumstances, the final instance
2610was overriding all earlier ones. [perl #113584]
2611
2612=item *
2613
2614Regular expressions like C<qr/\87/> previously silently inserted a NUL
2615character, thus matching as if it had been written C<qr/\00087/>. Now it
2616matches as if it had been written as C<qr/87/>, with a message that the
2617sequence C<"\8"> is unrecognized.
2618
2619=item *
2620
2621C<__SUB__> now works in special blocks (C<BEGIN>, C<END>, etc.).
2622
2623=item *
2624
2625Thread creation on Windows could theoretically result in a crash if done
2626inside a C<BEGIN> block. It still does not work properly, but it no longer
2627crashes [perl #111610].
2628
2629=item *
2630
2631C<\&{''}> (with the empty string) now autovivifies a stub like any other
2632sub name, and no longer produces the "Unable to create sub" error
2633[perl #94476].
2634
2635=item *
2636
2637A regression introduced in v5.14.0 has been fixed, in which some calls
2638to the C<re> module would clobber C<$_> [perl #113750].
2639
2640=item *
2641
2642C<do FILE> now always either sets or clears C<$@>, even when the file can't be
2643read. This ensures that testing C<$@> first (as recommended by the
2644documentation) always returns the correct result.
2645
2646=item *
2647
2648The array iterator used for the C<each @array> construct is now correctly
2649reset when C<@array> is cleared (RT #75596). This happens for example when the
2650array is globally assigned to, as in C<@array = (...)>, but not when its
2651B<values> are assigned to. In terms of the XS API, it means that C<av_clear()>
2652will now reset the iterator.
2653
2654This mirrors the behaviour of the hash iterator when the hash is cleared.
2655
2656=item *
2657
2658C<< $class->can >>, C<< $class->isa >>, and C<< $class->DOES >> now return
2659correct results, regardless of whether that package referred to by C<$class>
2660exists [perl #47113].
2661
2662=item *
2663
2664Arriving signals no longer clear C<$@> [perl #45173].
2665
2666=item *
2667
2668Allow C<my ()> declarations with an empty variable list [perl #113554].
2669
2670=item *
2671
2672During parsing, subs declared after errors no longer leave stubs
2673[perl #113712].
2674
2675=item *
2676
2677Closures containing no string evals no longer hang on to their containing
2678subroutines, allowing variables closed over by outer subroutines to be
2679freed when the outer sub is freed, even if the inner sub still exists
2680[perl #89544].
2681
2682=item *
2683
2684Duplication of in-memory filehandles by opening with a "<&=" or ">&=" mode
2685stopped working properly in 5.16.0. It was causing the new handle to
2686reference a different scalar variable. This has been fixed [perl #113764].
2687
2688=item *
2689
2690C<qr//> expressions no longer crash with custom regular expression engines
2691that do not set C<offs> at regular expression compilation time
2692[perl #112962].
2693
2694=item *
2695
2696C<delete local> no longer crashes with certain magical arrays and hashes
2697[perl #112966].
2698
2699=item *
2700
2701C<local> on elements of certain magical arrays and hashes used not to
2702arrange to have the element deleted on scope exit, even if the element did
2703not exist before C<local>.
2704
2705=item *
2706
2707C<scalar(write)> no longer returns multiple items [perl #73690].
2708
2709=item *
2710
2711String to floating point conversions no longer misparse certain strings under
2712C<use locale> [perl #109318].
2713
2714=item *
2715
2716C<@INC> filters that die no longer leak memory [perl #92252].
2717
2718=item *
2719
2720The implementations of overloaded operations are now called in the correct
2721context. This allows, among other things, being able to properly override
2722C<< <> >> [perl #47119].
2723
2724=item *
2725
2726Specifying only the C<fallback> key when calling C<use overload> now behaves
2727properly [perl #113010].
2728
2729=item *
2730
2731C<< sub foo { my $a = 0; while ($a) { ... } } >> and
2732C<< sub foo { while (0) { ... } } >> now return the same thing [perl #73618].
2733
2734=item *
2735
2736String negation now behaves the same under C<use integer;> as it does
2737without [perl #113012].
2738
2739=item *
2740
2741C<chr> now returns the Unicode replacement character (U+FFFD) for -1,
2742regardless of the internal representation. -1 used to wrap if the argument
2743was tied or a string internally.
2744
2745=item *
2746
2747Using a C<format> after its enclosing sub was freed could crash as of
2748perl 5.12.0, if the format referenced lexical variables from the outer sub.
2749
2750=item *
2751
2752Using a C<format> after its enclosing sub was undefined could crash as of
2753perl 5.10.0, if the format referenced lexical variables from the outer sub.
2754
2755=item *
2756
2757Using a C<format> defined inside a closure, which format references
2758lexical variables from outside, never really worked unless the C<write>
2759call was directly inside the closure. In 5.10.0 it even started crashing.
2760Now the copy of that closure nearest the top of the call stack is used to
2761find those variables.
2762
2763=item *
2764
2765Formats that close over variables in special blocks no longer crash if a
2766stub exists with the same name as the special block before the special
2767block is compiled.
2768
2769=item *
2770
2771The parser no longer gets confused, treating C<eval foo ()> as a syntax
2772error if preceded by C<print;> [perl #16249].
2773
2774=item *
2775
2776The return value of C<syscall> is no longer truncated on 64-bit platforms
2777[perl #113980].
2778
2779=item *
2780
2781Constant folding no longer causes C<print 1 ? FOO : BAR> to print to the
2782FOO handle [perl #78064].
2783
2784=item *
2785
2786C<do subname> now calls the named subroutine and uses the file name it
2787returns, instead of opening a file named "subname".
2788
2789=item *
2790
2791Subroutines looked up by rv2cv check hooks (registered by XS modules) are
2792now taken into consideration when determining whether C<foo bar> should be
2793the sub call C<foo(bar)> or the method call C<< "bar"->foo >>.
2794
2795=item *
2796
2797C<CORE::foo::bar> is no longer treated specially, allowing global overrides
2798to be called directly via C<CORE::GLOBAL::uc(...)> [perl #113016].
2799
2800=item *
2801
2802Calling an undefined sub whose typeglob has been undefined now produces the
2803customary "Undefined subroutine called" error, instead of "Not a CODE
2804reference".
2805
2806=item *
2807
2808Two bugs involving @ISA have been fixed. C<*ISA = *glob_without_array> and
2809C<undef *ISA; @{*ISA}> would prevent future modifications to @ISA from
2810updating the internal caches used to look up methods. The
2811*glob_without_array case was a regression from Perl 5.12.
2812
2813=item *
2814
2815Regular expression optimisations sometimes caused C<$> with C</m> to
2816produce failed or incorrect matches [perl #114068].
2817
2818=item *
2819
2820C<__SUB__> now works in a C<sort> block when the enclosing subroutine is
2821predeclared with C<sub foo;> syntax [perl #113710].
2822
2823=item *
2824
2825Unicode properties only apply to Unicode code points, which leads to
2826some subtleties when regular expressions are matched against
2827above-Unicode code points. There is a warning generated to draw your
2828attention to this. However, this warning was being generated
2829inappropriately in some cases, such as when a program was being parsed.
2830Non-Unicode matches such as C<\w> and C<[:word;]> should not generate the
2831warning, as their definitions don't limit them to apply to only Unicode
2832code points. Now the message is only generated when matching against
2833C<\p{}> and C<\P{}>. There remains a bug, [perl #114148], for the very
2834few properties in Unicode that match just a single code point. The
2835warning is not generated if they are matched against an above-Unicode
2836code point.
2837
2838=item *
2839
2840Uninitialized warnings mentioning hash elements would only mention the
2841element name if it was not in the first bucket of the hash, due to an
2842off-by-one error.
2843
2844=item *
2845
2846A regular expression optimizer bug could cause multiline "^" to behave
2847incorrectly in the presence of line breaks, such that
2848C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].
2849
2850=item *
2851
2852Failed C<fork> in list context no longer corrupts the stack.
2853C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
2854if the C<fork> call failed.
2855
2856=item *
2857
2858Numerous memory leaks have been fixed, mostly involving tied variables that
2859die, regular expression character classes and code blocks, and syntax
2860errors.
2861
2862=item *
2863
2864Assigning a regular expression (C<${qr//}>) to a variable that happens to
2865hold a floating point number no longer causes assertion failures on
2866debugging builds.
2867
2868=item *
2869
2870Assigning a regular expression to a scalar containing a number no longer
2871causes subsequent nummification to produce random numbers.
2872
2873=item *
2874
2875Assigning a regular expression to a magic variable no longer wipes away the
2ae351f8 2876magic. This was a regression from 5.10.
5ed58cbd
RS
2877
2878=item *
2879
2880Assigning a regular expression to a blessed scalar no longer results in
2ae351f8 2881crashes. This was also a regression from 5.10.
5ed58cbd
RS
2882
2883=item *
2884
2885Regular expression can now be assigned to tied hash and array elements with
2886flattening into strings.
2887
2888=item *
2889
2890Nummifying a regular expression no longer results in an uninitialized
2891warning.
2892
2893=item *
2894
2895Negative array indices no longer cause EXISTS methods of tied variables to
2ae351f8 2896be ignored. This was a regression from 5.12.
5ed58cbd
RS
2897
2898=item *
2899
2900Negative array indices no longer result in crashes on arrays tied to
2901non-objects.
2902
2903=item *
2904
2905C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF8 if the
2906left-hand scalar happened to have produced a UTF8 string the last time
2907overloading was invoked.
2908
2909=item *
2910
2911C<goto &sub> now uses the current value of @_, instead of using the array
2912the subroutine was originally called with. This means
2913C<local @_ = (...); goto &sub> now works [perl #43077].
2914
2915=item *
2916
2917If a debugger is invoked recursively, it no longer stomps on its own
2918lexical variables. Formerly under recursion all calls would share the same
2919set of lexical variables [perl #115742].
2920
2921=item *
2922
2923C<*_{ARRAY}> returned from a subroutine no longer spontaneously
2924becomes empty.
2925
2926=back
2927
2928=head1 Known Problems
2929
2930=over 4
2931
2932=item *
2933
2934XXX: the imperfect behavior of the ** deprecation
2935
2936=back
2937
2938=head1 Acknowledgements
a75569c0 2939
5ed58cbd 2940XXX Generate this with:
a75569c0 2941
5ed58cbd 2942 perl Porting/acknowledgements.pl v5.18.0..HEAD
f5b73711 2943
44691e6f
AB
2944=head1 Reporting Bugs
2945
e08634c5
SH
2946If you find what you think is a bug, you might check the articles recently
2947posted to the comp.lang.perl.misc newsgroup and the perl bug database at
2948http://rt.perl.org/perlbug/ . There may also be information at
2949http://www.perl.org/ , the Perl Home Page.
44691e6f 2950
e08634c5
SH
2951If you believe you have an unreported bug, please run the L<perlbug> program
2952included with your release. Be sure to trim your bug down to a tiny but
2953sufficient test case. Your bug report, along with the output of C<perl -V>,
2954will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
44691e6f
AB
2955
2956If the bug you are reporting has security implications, which make it
e08634c5
SH
2957inappropriate to send to a publicly archived mailing list, then please send it
2958to perl5-security-report@perl.org. This points to a closed subscription
2959unarchived mailing list, which includes all the core committers, who will be
2960able to help assess the impact of issues, figure out a resolution, and help
f9001595 2961co-ordinate the release of patches to mitigate or fix the problem across all
e08634c5
SH
2962platforms on which Perl is supported. Please only use this address for
2963security issues in the Perl core, not for modules independently distributed on
2964CPAN.
44691e6f
AB
2965
2966=head1 SEE ALSO
2967
e08634c5
SH
2968The F<Changes> file for an explanation of how to view exhaustive details on
2969what changed.
44691e6f
AB
2970
2971The F<INSTALL> file for how to build Perl.
2972
2973The F<README> file for general stuff.
2974
2975The F<Artistic> and F<Copying> files for copyright information.
2976
2977=cut