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perldelta: use v5.x rather than 5.x
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1=encoding utf8
2
3=head1 NAME
4
5ed58cbd 5perldelta - what is new for perl v5.18.0
e128ab2c 6
4eabcf70 7=head1 DESCRIPTION
6db9054f 8
e612b5a0 9This document describes differences between the v5.16.0 release and the v5.18.0
e08634c5 10release.
6db9054f 11
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12If you are upgrading from an earlier release such as v5.14.0, first read
13L<perl5160delta>, which describes differences between v5.14.0 and v5.16.0.
3f01b192 14
5ed58cbd 15=head1 Core Enhancements
3f01b192 16
5ed58cbd 17=head2 New mechanism for experimental features
82d98f72 18
5ed58cbd 19Newly-added experimental features will now require this incantation:
82d98f72 20
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21 no warnings "experimental::feature_name";
22 use feature "feature_name"; # would warn without the prev line
23
24There is a new warnings category, called "experimental", containing
25warnings that the L<feature> pragma emits when enabling experimental
26features.
27
28Newly-added experimental features will also be given special warning IDs,
29which consist of "experimental::" followed by the name of the feature. (The
30plan is to extend this mechanism eventually to all warnings, to allow them
31to be enabled or disabled individually, and not just by category.)
32
33By saying
34
35 no warnings "experimental::feature_name";
36
37you are taking responsibility for any breakage that future changes to, or
38removal of, the feature may cause.
39
40Existing experimental features may begin emitting these warnings, too. Please
41consult L<perlexperiment> for information on which features are considered
42experimental.
43
44=head2 Hash overhaul
45
e612b5a0 46Changes to the implementation of hashes in perl v5.18.0 will be one of the most
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47visible changes to the behavior of existing code.
48
8e74b2ed 49By default, two distinct hash variables with identical keys and values may now
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50provide their contents in a different order where it was previously identical.
51
52When encountering these changes, the key to cleaning up from them is to accept
53that B<hashes are unordered collections> and to act accordingly.
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54
55=head3 Hash randomization
56
57The seed used by Perl's hash function is now random. This means that the
58order which keys/values will be returned from functions like C<keys()>,
59C<values()>, and C<each()> will differ from run to run.
60
61This change was introduced to make Perl's hashes more robust to algorithmic
62complexity attacks, and also because we discovered that it exposes hash
63ordering dependency bugs and makes them easier to track down.
64
65Toolchain maintainers might want to invest in additional infrastructure to
66test for things like this. Running tests several times in a row and then
67comparing results will make it easier to spot hash order dependencies in
68code. Authors are strongly encouraged not to expose the key order of
69Perl's hashes to insecure audiences.
70
71Further, every hash has its own iteration order, which should make it much
72more difficult to determine what the current hash seed is.
73
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74=head3 New hash functions
75
e612b5a0 76Perl v5.18 includes support for multiple hash functions, and changed
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77the default (to ONE_AT_A_TIME_HARD), you can choose a different
78algorithm by defining a symbol at compile time. For a current list,
e612b5a0 79consult the F<INSTALL> document. Note that as of Perl v5.18 we can
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80only recommend use of the default or SIPHASH. All the others are
81known to have security issues and are for research purposes only.
5ed58cbd 82
f105b7be 83=head3 PERL_HASH_SEED environment variable now takes a hex value
5ed58cbd 84
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85C<PERL_HASH_SEED> no longer accepts an integer as a parameter;
86instead the value is expected to be a binary value encoded in a hex
87string, such as "0xf5867c55039dc724". This is to make the
88infrastructure support hash seeds of arbitrary lengths, which might
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89exceed that of an integer. (SipHash uses a 16 byte seed).
90
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91=head3 PERL_PERTURB_KEYS environment variable added
92
f105b7be 93The C<PERL_PERTURB_KEYS> environment variable allows one to control the level of
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94randomization applied to C<keys> and friends.
95
f105b7be 96When C<PERL_PERTURB_KEYS> is 0, perl will not randomize the key order at all. The
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97chance that C<keys> changes due to an insert will be the same as in previous
98perls, basically only when the bucket size is changed.
99
f105b7be 100When C<PERL_PERTURB_KEYS> is 1, perl will randomize keys in a non-repeatable
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101way. The chance that C<keys> changes due to an insert will be very high. This
102is the most secure and default mode.
103
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104When C<PERL_PERTURB_KEYS> is 2, perl will randomize keys in a repeatable way.
105Repeated runs of the same program should produce the same output every time.
c40c48bb 106
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107C<PERL_HASH_SEED> implies a non-default C<PERL_PERTURB_KEYS> setting. Setting
108C<PERL_HASH_SEED=0> (exactly one 0) implies C<PERL_PERTURB_KEYS=0> (hash key
109randomization disabled); settng C<PERL_HASH_SEED> to any other value implies
110C<PERL_PERTURB_KEYS=2> (deterministic and repeatable hash key randomization).
111Specifying C<PERL_PERTURB_KEYS> explicitly to a different level overrides this
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112behavior.
113
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114=head3 Hash::Util::hash_seed() now returns a string
115
116Hash::Util::hash_seed() now returns a string instead of an integer. This
117is to make the infrastructure support hash seeds of arbitrary lengths
118which might exceed that of an integer. (SipHash uses a 16 byte seed).
119
120=head3 Output of PERL_HASH_SEED_DEBUG has been changed
121
122The environment variable PERL_HASH_SEED_DEBUG now makes perl show both the
f105b7be 123hash function perl was built with, I<and> the seed, in hex, in use for that
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124process. Code parsing this output, should it exist, must change to accommodate
125the new format. Example of the new format:
126
127 $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
128 HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f
129
130=head2 Upgrade to Unicode 6.2
131
2e7bc647 132Perl now supports Unicode 6.2. A list of changes from Unicode
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1336.1 is at L<http://www.unicode.org/versions/Unicode6.2.0>.
134
135=head2 Character name aliases may now include non-Latin1-range characters
136
137It is possible to define your own names for characters for use in
138C<\N{...}>, C<charnames::vianame()>, etc. These names can now be
139comprised of characters from the whole Unicode range. This allows for
140names to be in your native language, and not just English. Certain
141restrictions apply to the characters that may be used (you can't define
142a name that has punctuation in it, for example). See L<charnames/CUSTOM
143ALIASES>.
144
145=head2 New DTrace probes
146
147The following new DTrace probes have been added:
14731ad1 148
337fb649 149=over 4
14731ad1 150
82d98f72 151=item *
14731ad1 152
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153C<op-entry>
154
155=item *
156
157C<loading-file>
158
159=item *
160
161C<loaded-file>
162
163=back
164
165=head2 C<${^LAST_FH}>
166
167This new variable provides access to the filehandle that was last read.
168This is the handle used by C<$.> and by C<tell> and C<eof> without
169arguments.
170
171=head2 Regular Expression Set Operations
172
173This is an B<experimental> feature to allow matching against the union,
174intersection, etc., of sets of code points, similar to
175L<Unicode::Regex::Set>. It can also be used to extend C</x> processing
176to [bracketed] character classes, and as a replacement of user-defined
177properties, allowing more complex expressions than they do. See
178L<perlrecharclass/Extended Bracketed Character Classes>.
179
180=head2 Lexical subroutines
181
182This new feature is still considered B<experimental>. To enable it:
183
184 use 5.018;
185 no warnings "experimental::lexical_subs";
186 use feature "lexical_subs";
187
188You can now declare subroutines with C<state sub foo>, C<my sub foo>, and
189C<our sub foo>. (C<state sub> requires that the "state" feature be
190enabled, unless you write it as C<CORE::state sub foo>.)
191
192C<state sub> creates a subroutine visible within the lexical scope in which
193it is declared. The subroutine is shared between calls to the outer sub.
194
195C<my sub> declares a lexical subroutine that is created each time the
196enclosing block is entered. C<state sub> is generally slightly faster than
197C<my sub>.
198
199C<our sub> declares a lexical alias to the package subroutine of the same
200name.
201
202For more information, see L<perlsub/Lexical Subroutines>.
203
204=head2 Computed Labels
205
206The loop controls C<next>, C<last> and C<redo>, and the special C<dump>
207operator, now allow arbitrary expressions to be used to compute labels at run
208time. Previously, any argument that was not a constant was treated as the
209empty string.
210
211=head2 More CORE:: subs
212
213Several more built-in functions have been added as subroutines to the
214CORE:: namespace - namely, those non-overridable keywords that can be
215implemented without custom parsers: C<defined>, C<delete>, C<exists>,
216C<glob>, C<pos>, C<protoytpe>, C<scalar>, C<split>, C<study>, and C<undef>.
217
218As some of these have prototypes, C<prototype('CORE::...')> has been
219changed to not make a distinction between overridable and non-overridable
220keywords. This is to make C<prototype('CORE::pos')> consistent with
221C<prototype(&CORE::pos)>.
222
223=head2 C<kill> with negative signal names
224
225C<kill> has always allowed a negative signal number, which kills the
226process group instead of a single process. It has also allowed signal
227names. But it did not behave consistently, because negative signal names
228were treated as 0. Now negative signals names like C<-INT> are supported
229and treated the same way as -2 [perl #112990].
230
231=head1 Security
232
233=head2 C<Storable> security warning in documentation
234
235The documentation for C<Storable> now includes a section which warns readers
236of the danger of accepting Storable documents from untrusted sources. The
237short version is that deserializing certain types of data can lead to loading
238modules and other code execution. This is documented behavior and wanted
239behavior, but this opens an attack vector for malicious entities.
240
241=head2 C<Locale::Maketext> allowed code injection via a malicious template
242
243If users could provide a translation string to Locale::Maketext, this could be
244used to invoke arbitrary Perl subroutines available in the current process.
245
246This has been fixed, but it is still possible to invoke any method provided by
247C<Locale::Maketext> itself or a subclass that you are using. One of these
248methods in turn will invoke the Perl core's C<sprintf> subroutine.
249
250In summary, allowing users to provide translation strings without auditing
251them is a bad idea.
252
253This vulnerability is documented in CVE-2012-6329.
254
255=head2 Avoid calling memset with a negative count
256
257Poorly written perl code that allows an attacker to specify the count to perl's
258C<x> string repeat operator can already cause a memory exhaustion
e612b5a0 259denial-of-service attack. A flaw in versions of perl before v5.15.5 can escalate
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260that into a heap buffer overrun; coupled with versions of glibc before 2.16, it
261possibly allows the execution of arbitrary code.
262
263The flaw addressed to this commit has been assigned identifier CVE-2012-5195
264and was researched by Tim Brown.
265
266=head1 Incompatible Changes
267
268=head2 See also: hash overhaul
269
270Some of the changes in the L<hash overhaul|/"Hash overhaul"> are not fully
271compatible with previous versions of perl. Please read that section.
272
273=head2 An unknown character name in C<\N{...}> is now a syntax error
274
275Previously, it warned, and the Unicode REPLACEMENT CHARACTER was
276substituted. Unicode now recommends that this situation be a syntax
277error. Also, the previous behavior led to some confusing warnings and
278behaviors, and since the REPLACEMENT CHARACTER has no use other than as
279a stand-in for some unknown character, any code that has this problem is
280buggy.
281
282=head2 Formerly deprecated characters in C<\N{}> character name aliases are now errors.
283
284Since v5.12.0, it has been deprecated to use certain characters in
285user-defined C<\N{...}> character names. These now cause a syntax
286error. For example, it is now an error to begin a name with a digit,
287such as in
288
289 my $undraftable = "\N{4F}"; # Syntax error!
290
291or to have commas anywhere in the name. See L<charnames/CUSTOM ALIASES>
292
293=head2 C<\N{BELL}> now refers to U+1F514 instead of U+0007
294
295Unicode 6.0 reused the name "BELL" for a different code point than it
296traditionally had meant. Since Perl v5.14, use of this name still
297referred to U+0007, but would raise a deprecation warning. Now, "BELL"
298refers to U+1F514, and the name for U+0007 is "ALERT". All the
299functions in L<charnames> have been correspondingly updated.
300
301=head2 New Restrictions in Multi-Character Case-Insensitive Matching in Regular Expression Bracketed Character Classes
302
303Unicode has now withdrawn their previous recommendation for regular
304expressions to automatically handle cases where a single character can
305match multiple characters case-insensitively, for example the letter
306LATIN SMALL LETTER SHARP S and the sequence C<ss>. This is because
307it turns out to be impracticable to do this correctly in all
308circumstances. Because Perl has tried to do this as best it can, it
309will continue to do so. (We are considering an option to turn it off.)
310However, a new restriction is being added on such matches when they
311occur in [bracketed] character classes. People were specifying
312things such as C</[\0-\xff]/i>, and being surprised that it matches the
313two character sequence C<ss> (since LATIN SMALL LETTER SHARP S occurs in
314this range). This behavior is also inconsistent with using a
315property instead of a range: C<\p{Block=Latin1}> also includes LATIN
316SMALL LETTER SHARP S, but C</[\p{Block=Latin1}]/i> does not match C<ss>.
317The new rule is that for there to be a multi-character case-insensitive
318match within a bracketed character class, the character must be
319explicitly listed, and not as an end point of a range. This more
320closely obeys the Principle of Least Astonishment. See
321L<perlrecharclass/Bracketed Character Classes>. Note that a bug [perl
322#89774], now fixed as part of this change, prevented the previous
323behavior from working fully.
324
325=head2 Explicit rules for variable names and identifiers
326
e612b5a0 327Due to an oversight, length-one variable names in v5.16 were completely
5ed58cbd 328unrestricted, and opened the door to several kinds of insanity. As of
e612b5a0 329v5.18, these now follow the rules of other identifiers, in addition
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330to accepting characters that match the C<\p{POSIX_Punct}> property.
331
332There are no longer any differences in the parsing of identifiers
333specified as C<$...> or C<${...}>; previously, they were dealt with in
334different parts of the core, and so had slightly different behavior. For
335instance, C<${foo:bar}> was a legal variable name. Since they are now
336both parsed by the same code, that is no longer the case.
337
338=head2 C<\s> in regular expressions now matches a Vertical Tab
339
340No one could recall why C<\s> didn't match C<\cK>, the vertical tab.
341Now it does. Given the extreme rarity of that character, very little
342breakage is expected.
343
344=head2 C</(?{})/> and C</(??{})/> have been heavily reworked
345
346The implementation of this feature has been almost completely rewritten.
347Although its main intent is to fix bugs, some behaviors, especially
348related to the scope of lexical variables, will have changed. This is
349described more fully in the L</Selected Bug Fixes> section.
350
351=head2 Stricter parsing of substitution replacement
352
353It is no longer possible to abuse the way the parser parses C<s///e> like
354this:
355
356 %_=(_,"Just another ");
357 $_="Perl hacker,\n";
358 s//_}->{_/e;print
359
360=head2 C<given> now aliases the global C<$_>
361
362Instead of assigning to an implicit lexical C<$_>, C<given> now makes the
363global C<$_> an alias for its argument, just like C<foreach>. However, it
364still uses lexical C<$_> if there is lexical C<$_> in scope (again, just like
365C<foreach>) [perl #114020].
366
367=head2 Lexical C<$_> is now experimental
368
e612b5a0 369Since it was introduced in Perl v5.10, it has caused much confusion with no
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370obvious solution:
371
372=over
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373
374=item *
375
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376Various modules (e.g., List::Util) expect callback routines to use the
377global C<$_>. C<use List::Util 'first'; my $_; first { $_ == 1 } @list>
378does not work as one would expect.
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379
380=item *
381
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382A C<my $_> declaration earlier in the same file can cause confusing closure
383warnings.
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384
385=item *
386
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387The "_" subroutine prototype character allows called subroutines to access
388your lexical C<$_>, so it is not really private after all.
2426c394 389
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390=item *
391
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392Nevertheless, subroutines with a "(@)" prototype and methods cannot access
393the caller's lexical C<$_>, unless they are written in XS.
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394
395=item *
396
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397But even XS routines cannot access a lexical C<$_> declared, not in the
398calling subroutine, but in an outer scope, iff that subroutine happened not
399to mention C<$_> or use any operators that default to C<$_>.
400
401=back
402
403It is our hope that lexical C<$_> can be rehabilitated, but this may
404cause changes in its behavior. Please use it with caution until it
405becomes stable.
406
407=head2 readline() with C<$/ = \N> now reads N characters, not N bytes
408
409Previously, when reading from a stream with I/O layers such as
410C<encoding>, the readline() function, otherwise known as the C<< <> >>
411operator, would read I<N> bytes from the top-most layer. [perl #79960]
412
413Now, I<N> characters are read instead.
414
415There is no change in behaviour when reading from streams with no
416extra layers, since bytes map exactly to characters.
417
418=head2 Overridden C<glob> is now passed one argument
419
420C<glob> overrides used to be passed a magical undocumented second argument
421that identified the caller. Nothing on CPAN was using this, and it got in
422the way of a bug fix, so it was removed. If you really need to identify
423the caller, see L<Devel::Callsite> on CPAN.
424
425=head2 Here-doc parsing
426
427The body of a here-document inside a quote-like operator now always begins
428on the line after the "<<foo" marker. Previously, it was documented to
429begin on the line following the containing quote-like operator, but that
430was only sometimes the case [perl #114040].
431
432=head2 Alphanumeric operators must now be separated from the closing
433delimiter of regular expressions
434
435You may no longer write something like:
436
437 m/a/and 1
438
439Instead you must write
440
441 m/a/ and 1
442
443with whitespace separating the operator from the closing delimiter of
444the regular expression. Not having whitespace has resulted in a
445deprecation warning since Perl v5.14.0.
446
447=head2 qw(...) can no longer be used as parentheses
448
449C<qw> lists used to fool the parser into thinking they were always
450surrounded by parentheses. This permitted some surprising constructions
451such as C<foreach $x qw(a b c) {...}>, which should really be written
452C<foreach $x (qw(a b c)) {...}>. These would sometimes get the lexer into
453the wrong state, so they didn't fully work, and the similar C<foreach qw(a
454b c) {...}> that one might expect to be permitted never worked at all.
455
456This side effect of C<qw> has now been abolished. It has been deprecated
e612b5a0 457since Perl v5.13.11. It is now necessary to use real parentheses
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458everywhere that the grammar calls for them.
459
460=head2 Interaction of lexical and default warnings
461
462Turning on any lexical warnings used first to disable all default warnings
463if lexical warnings were not already enabled:
464
465 $*; # deprecation warning
466 use warnings "void";
467 $#; # void warning; no deprecation warning
468
f105b7be 469Now, the C<debugging>, C<deprecated>, C<glob>, C<inplace> and C<malloc> warnings
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470categories are left on when turning on lexical warnings (unless they are
471turned off by C<no warnings>, of course).
472
473This may cause deprecation warnings to occur in code that used to be free
474of warnings.
475
476Those are the only categories consisting only of default warnings. Default
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477warnings in other categories are still disabled by C<< use warnings "category" >>,
478as we do not yet have the infrastructure for controlling
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479individual warnings.
480
481=head2 C<state sub> and C<our sub>
482
483Due to an accident of history, C<state sub> and C<our sub> were equivalent
484to a plain C<sub>, so one could even create an anonymous sub with
485C<our sub { ... }>. These are now disallowed outside of the "lexical_subs"
486feature. Under the "lexical_subs" feature they have new meanings described
487in L<perlsub/Lexical Subroutines>.
488
489=head2 Defined values stored in environment are forced to byte strings
490
491A value stored in an environment variable has always been stringified. In this
492release, it is converted to be only a byte string. First, it is forced to be a
493only a string. Then if the string is utf8 and the equivalent of
494C<utf8::downgrade()> works, that result is used; otherwise, the equivalent of
495C<utf8::encode()> is used, and a warning is issued about wide characters
496(L</Diagnostics>).
497
498=head2 C<require> dies for unreadable files
499
500When C<require> encounters an unreadable file, it now dies. It used to
501ignore the file and continue searching the directories in C<@INC>
502[perl #113422].
503
504=head2 C<gv_fetchmeth_*> and SUPER
505
506The various C<gv_fetchmeth_*> XS functions used to treat a package whose
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507named ended with C<::SUPER> specially. A method lookup on the C<Foo::SUPER>
508package would be treated as a C<SUPER> method lookup on the C<Foo> package. This
509is no longer the case. To do a C<SUPER> lookup, pass the C<Foo> stash and the
510C<GV_SUPER> flag.
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511
512=head2 C<split>'s first argument is more consistently interpreted
513
e612b5a0 514After some changes earlier in v5.17, C<split>'s behavior has been
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515simplified: if the PATTERN argument evaluates to a literal string
516containing one space, it is treated the way that a I<literal> string
517containing one space once was.
518
519=head1 Deprecations
520
521=head2 Deprecated modules
522
523The following modules will be removed from the core distribution in a
524future release, and should be installed from CPAN instead. Distributions
525on CPAN which require these should add them to their prerequisites.
f105b7be 526The core versions of these modules will issue C<"deprecated">-category
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527warnings.
528
529You can silence these deprecation warnings by installing the modules
530in question from CPAN.
531
532=over
533
534=item L<Archive::Extract>
535
536=item L<B::Lint>
537
538=item L<B::Lint::Debug>
539
540=item L<CPANPLUS> and all included C<CPANPLUS::*> modules
541
542=item L<Devel::InnerPackage>
543
544=item L<encoding>
545
546=item L<Log::Message>
547
548=item L<Log::Message::Config>
549
550=item L<Log::Message::Handlers>
551
552=item L<Log::Message::Item>
553
554=item L<Log::Message::Simple>
555
556=item L<Module::Pluggable>
557
558=item L<Module::Pluggable::Object>
559
560=item L<Object::Accessor>
561
562=item L<Pod::LaTeX>
563
564=item L<Term::UI>
565
566=item L<Term::UI::History>
567
568=back
569
570=head2 Deprecated Utilities
571
572The following utilities will be removed from the core distribution in a
573future release as their associated modules have been deprecated. They
574will remain available with the applicable CPAN distribution.
575
576=over
577
578=item L<cpanp>
579
580=item C<cpanp-run-perl>
581
582=item L<cpan2dist>
583
584These items are part of the C<CPANPLUS> distribution.
585
586=item L<pod2latex>
587
588This item is part of the C<Pod::LaTeX> distribution.
589
590=back
591
592=head2 PL_sv_objcount
593
594This interpreter-global variable used to track the total number of
595Perl objects in the interpreter. It is no longer maintained and will
e612b5a0 596be removed altogether in Perl v5.20.
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597
598=head2 Five additional characters should be escaped in patterns with C</x>
599
600When a regular expression pattern is compiled with C</x>, Perl treats 6
601characters as white space to ignore, such as SPACE and TAB. However,
602Unicode recommends 11 characters be treated thusly. We will conform
603with this in a future Perl version. In the meantime, use of any of the
604missing characters will raise a deprecation warning, unless turned off.
605The five characters are:
f105b7be
KE
606
607 U+0085 NEXT LINE,
608 U+200E LEFT-TO-RIGHT MARK,
609 U+200F RIGHT-TO-LEFT MARK,
610 U+2028 LINE SEPARATOR,
611
5ed58cbd 612and
f105b7be
KE
613
614 U+2029 PARAGRAPH SEPARATOR.
5ed58cbd
RS
615
616=head2 User-defined charnames with surprising whitespace
617
618A user-defined character name with trailing or multiple spaces in a row is
619likely a typo. This now generates a warning when defined, on the assumption
620that uses of it will be unlikely to include the excess whitespace.
621
622=head2 Various XS-callable functions are now deprecated
623
624All the functions used to classify characters will be removed from a
625future version of Perl, and should not be used. With participating C
626compilers (e.g., gcc), compiling any file that uses any of these will
627generate a warning. These were not intended for public use; there are
628equivalent, faster, macros for most of them.
e612b5a0 629
2e7bc647 630See L<perlapi/Character classes>. The complete list is:
e612b5a0 631
5ed58cbd
RS
632C<is_uni_alnum>, C<is_uni_alnumc>, C<is_uni_alnumc_lc>,
633C<is_uni_alnum_lc>, C<is_uni_alpha>, C<is_uni_alpha_lc>,
634C<is_uni_ascii>, C<is_uni_ascii_lc>, C<is_uni_blank>,
635C<is_uni_blank_lc>, C<is_uni_cntrl>, C<is_uni_cntrl_lc>,
636C<is_uni_digit>, C<is_uni_digit_lc>, C<is_uni_graph>,
637C<is_uni_graph_lc>, C<is_uni_idfirst>, C<is_uni_idfirst_lc>,
638C<is_uni_lower>, C<is_uni_lower_lc>, C<is_uni_print>,
639C<is_uni_print_lc>, C<is_uni_punct>, C<is_uni_punct_lc>,
640C<is_uni_space>, C<is_uni_space_lc>, C<is_uni_upper>,
641C<is_uni_upper_lc>, C<is_uni_xdigit>, C<is_uni_xdigit_lc>,
642C<is_utf8_alnum>, C<is_utf8_alnumc>, C<is_utf8_alpha>,
643C<is_utf8_ascii>, C<is_utf8_blank>, C<is_utf8_char>,
644C<is_utf8_cntrl>, C<is_utf8_digit>, C<is_utf8_graph>,
645C<is_utf8_idcont>, C<is_utf8_idfirst>, C<is_utf8_lower>,
646C<is_utf8_mark>, C<is_utf8_perl_space>, C<is_utf8_perl_word>,
647C<is_utf8_posix_digit>, C<is_utf8_print>, C<is_utf8_punct>,
648C<is_utf8_space>, C<is_utf8_upper>, C<is_utf8_xdigit>,
649C<is_utf8_xidcont>, C<is_utf8_xidfirst>.
650
651In addition these three functions that have never worked properly are
652deprecated:
653C<to_uni_lower_lc>, C<to_uni_title_lc>, and C<to_uni_upper_lc>.
654
f105b7be 655=head2 Certain rare uses of backslashes within regexes are now deprecated
5ed58cbd
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656
657There are three pairs of characters that Perl recognizes as
658metacharacters in regular expression patterns: C<{}>, C<[]>, and C<()>.
659These can be used as well to delimit patterns, as in:
660
661 m{foo}
662 s(foo)(bar)
663
664Since they are metacharacters, they have special meaning to regular
665expression patterns, and it turns out that you can't turn off that
666special meaning by the normal means of preceding them with a backslash,
f105b7be 667if you use them, paired, within a pattern delimited by them. For
5ed58cbd
RS
668example, in
669
670 m{foo\{1,3\}}
671
672the backslashes do not change the behavior, and this matches
673S<C<"f o">> followed by one to three more occurrences of C<"o">.
674
675Usages like this, where they are interpreted as metacharacters, are
676exceedingly rare; we think there are none, for example, in all of CPAN.
677Hence, this deprecation should affect very little code. It does give
678notice, however, that any such code needs to change, which will in turn
679allow us to change the behavior in future Perl versions so that the
680backslashes do have an effect, and without fear that we are silently
681breaking any existing code.
682
d5f315e8
KW
683=head2 Splitting the tokens C<(?> and C<(*> in regular expressions
684
685A deprecation warning is now raised if the C<(> and C<?> are separated
686by white space or comments in C<(?...)> regular expression constructs.
687Similarly, if the C<(> and C<*> are separated in C<(*VERB...)>
688constructs.
689
e0a1dec5
LT
690=head2 Pre-PerlIO IO implementations
691
692Perl supports being built without PerlIO proper, using a stdio or sfio
693wrapper instead. A perl build like this will not support IO layers and
694thus Unicode IO, making it rather handicapped.
695
696PerlIO supports a C<stdio> layer if stdio use is desired, and similarly a
697sfio layer could be produced.
698
5ed58cbd
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699=head1 Future Deprecations
700
701=over
71e6aba6
RS
702
703=item *
704
4263dd11 705Platforms without support infrastructure
5ed58cbd
RS
706
707Both Windows CE and z/OS have been historically under-maintained, and are
708currently neither successfully building nor regularly being smoke tested.
709Efforts are underway to change this situation, but it should not be taken for
710granted that the platforms are safe and supported. If they do not become
711buildable and regularly smoked, support for them may be actively removed in
712future releases. If you have an interest in these platforms and you can lend
713your time, expertise, or hardware to help support these platforms, please let
714the perl development effort know by emailing C<perl5-porters@perl.org>.
715
716Some platforms that appear otherwise entirely dead are also on the short list
e612b5a0 717for removal between now and v5.20.0:
5ed58cbd
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718
719=over
720
721=item DG/UX
722
723=item NeXT
724
725=back
1993add8 726
ec985017
RS
727We also think it likely that current versions of Perl will no longer
728build AmigaOS, DJGPP, NetWare (natively), OS/2 and Plan 9. If you
729are using Perl on such a platform and have an interest in ensuring
730Perl's future on them, please contact us.
731
732We believe that Perl has long been unable to build on mixed endian
733architectures (such as PDP-11s), and intend to remove any remain
734support code. Similarly, code supporting the long umaintained GNU
735dld will be removed soon if no-one makes themselves known as an
736active user.
737
1993add8
RS
738=item *
739
5ed58cbd
RS
740Swapping of $< and $>
741
742For more information about this future deprecation, see L<the relevant RT
743ticket|https://rt.perl.org/rt3/Ticket/Display.html?id=96212>.
71e6aba6
RS
744
745=item *
746
5ed58cbd 747C<microperl>, long broken and of unclear present purpose, will be removed.
71e6aba6
RS
748
749=item *
750
5ed58cbd
RS
751Revamping C<< "\Q" >> semantics in double-quotish strings when combined with
752other escapes.
753
754There are several bugs and inconsistencies involving combinations
755of C<\Q> and escapes like C<\x>, C<\L>, etc., within a C<\Q...\E> pair.
756These need to be fixed, and doing so will necessarily change current
757behavior. The changes have not yet been settled.
71e6aba6 758
d5f315e8
KW
759=item *
760
761Use of C<$^>, where C<^> stands for any actual (non-printing) C0 control
762character will be disallowed in a future Perl version. Use C<${^}>
763instead (where again C<^> stands for a control character),
764or better, C<$^A> , where C<^> this time is a caret (CIRCUMFLEX ACCENT),
765and C<A> stands for any of the characters listed at the end of
766L<perlebcdic/OPERATOR DIFFERENCES>.
767
337fb649 768=back
2426c394 769
5ed58cbd
RS
770=head1 Performance Enhancements
771
772=over 4
2426c394 773
5ed58cbd 774=item *
2426c394 775
5ed58cbd
RS
776Lists of lexical variable declarations (C<my($x, $y)>) are now optimised
777down to a single op and are hence faster than before.
2426c394 778
5ed58cbd 779=item *
2426c394 780
5ed58cbd
RS
781A new C preprocessor define C<NO_TAINT_SUPPORT> was added that, if set,
782disables Perl's taint support altogether. Using the -T or -t command
783line flags will cause a fatal error. Beware that both core tests as
784well as many a CPAN distribution's tests will fail with this change. On
785the upside, it provides a small performance benefit due to reduced
786branching.
2426c394 787
5ed58cbd
RS
788B<Do not enable this unless you know exactly what you are getting yourself
789into.>
790
791=item *
792
793C<pack> with constant arguments is now constant folded in most cases
794[perl #113470].
795
796=item *
797
798Speed up in regular expression matching against Unicode properties. The
799largest gain is for C<\X>, the Unicode "extended grapheme cluster." The
800gain for it is about 35% - 40%. Bracketed character classes, e.g.,
801C<[0-9\x{100}]> containing code points above 255 are also now faster.
802
803=item *
804
805On platforms supporting it, several former macros are now implemented as static
806inline functions. This should speed things up slightly on non-GCC platforms.
807
808=item *
809
66f62cf6
RS
810The optimisation of hashes in boolean context has been extended to
811affect C<scalar(%hash)>, C<%hash ? ... : ...>, and C<sub { %hash || ... }>.
5ed58cbd
RS
812
813=item *
814
f105b7be 815Filetest operators manage the stack in a fractionally more efficient manner.
5ed58cbd
RS
816
817=item *
818
819Globs used in a numeric context are now numified directly in most cases,
f105b7be 820rather than being numified via stringification.
5ed58cbd
RS
821
822=item *
823
824The C<x> repetition operator is now folded to a single constant at compile
825time if called in scalar context with constant operands and no parentheses
826around the left operand.
827
828=back
829
830=head1 Modules and Pragmata
831
832=head2 New Modules and Pragmata
2426c394 833
337fb649 834=over 4
982110e0 835
82d98f72 836=item *
2426c394 837
5ed58cbd
RS
838L<Config::Perl::V> version 0.16 has been added as a dual-lifed module.
839It provides structured data retrieval of C<perl -V> output including
840information only known to the C<perl> binary and not available via L<Config>.
841
842=back
843
844=head2 Updated Modules and Pragmata
845
846This is only an overview of selected module updates. For a complete
847list of updates, run:
848
f105b7be 849 $ corelist --diff 5.16.0 5.18.0
5ed58cbd 850
e612b5a0 851You can substitute your favorite version in place of C<5.16.0>, too.
5ed58cbd
RS
852
853=over 4
33392251
BF
854
855=item *
856
5ed58cbd
RS
857L<XXX> has been upgraded from version A.xx to B.yy.
858
859=back
860
861=head2 Removed Modules and Pragmata
862
863=over
33392251
BF
864
865=item *
866
5ed58cbd
RS
867L<Version::Requirements> has been removed from the core distribution. It is
868available under a different name: L<CPAN::Meta::Requirements>.
2426c394 869
337fb649 870=back
2426c394 871
5ed58cbd 872=head1 Documentation
19718730 873
5ed58cbd
RS
874=head2 Changes to Existing Documentation
875
876=head3 L<perlcheat>
82d98f72 877
5a6a30f4 878=over 4
b7c7d786 879
5ed58cbd
RS
880=item *
881
882L<perlcheat> has been reorganized, and a few new sections were added.
883
884=back
885
886=head3 L<perldata>
887
888=over 4
82d98f72 889
5ed58cbd 890=item *
d2d1e842 891
5ed58cbd
RS
892Now explicitly documents the behaviour of hash initializer lists that
893contain duplicate keys.
f355e93d 894
5a6a30f4 895=back
f355e93d 896
5ed58cbd 897=head3 L<perldiag>
19718730 898
19718730 899=over 4
e14ac59b 900
5ed58cbd
RS
901=item *
902
903The explanation of symbolic references being prevented by "strict refs"
904now doesn't assume that the reader knows what symbolic references are.
905
906=back
9f351b45 907
5ed58cbd 908=head3 L<perlfaq>
9f351b45 909
5ed58cbd 910=over 4
9f351b45 911
5ed58cbd 912=item *
7cf3104f 913
5ed58cbd 914L<perlfaq> has been synchronized with version 5.0150040 from CPAN.
12719193 915
6253ee75 916=back
216cf7fc 917
5ed58cbd 918=head3 L<perlfunc>
f5b73711 919
5ed58cbd
RS
920=over 4
921
922=item *
a75569c0 923
5ed58cbd 924The return value of C<pipe> is now documented.
a75569c0 925
5ed58cbd 926=item *
a75569c0 927
5ed58cbd
RS
928Clarified documentation of C<our>.
929
930=back
931
932=head3 L<perlop>
933
934=over 4
935
936=item *
937
938Loop control verbs (C<dump>, C<goto>, C<next>, C<last> and C<redo>) have always
939had the same precedence as assignment operators, but this was not documented
940until now.
941
942=back
943
944=head3 Diagnostics
945
946The following additions or changes have been made to diagnostic output,
947including warnings and fatal error messages. For the complete list of
948diagnostic messages, see L<perldiag>.
949
950XXX New or changed warnings emitted by the core's C<C> code go here. Also
951include any changes in L<perldiag> that reconcile it to the C<C> code.
952
953=head2 New Diagnostics
954
955XXX Newly added diagnostic messages go under here, separated into New Errors
956and New Warnings
957
958=head3 New Errors
959
960=over 4
961
962=item *
963
964L<Unterminated delimiter for here document|perldiag/"Unterminated delimiter for here document">
965
966This message now occurs when a here document label has an initial quotation
967mark but the final quotation mark is missing.
968
969This replaces a bogus and misleading error message about not finding the label
970itself [perl #114104].
971
972=item *
973
974L<panic: child pseudo-process was never scheduled|perldiag/"panic: child pseudo-process was never scheduled">
975
976This error is thrown when a child pseudo-process in the ithreads implementation
977on Windows was not scheduled within the time period allowed and therefore was
978not able to initialize properly [perl #88840].
979
980=item *
981
982L<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/">
983
984This error has been added for C<(?&0)>, which is invalid. It used to
985produce an incomprehensible error message [perl #101666].
986
987=item *
988
989L<Can't use an undefined value as a subroutine reference|perldiag/"Can't use an undefined value as %s reference">
990
991Calling an undefined value as a subroutine now produces this error message.
992It used to, but was accidentally disabled, first in Perl 5.004 for
e612b5a0 993non-magical variables, and then in Perl v5.14 for magical (e.g., tied)
5ed58cbd
RS
994variables. It has now been restored. In the mean time, undef was treated
995as an empty string [perl #113576].
996
997=item *
998
999L<Experimental "%s" subs not enabled|perldiag/"Experimental "%s" subs not enabled">
1000
1001To use lexical subs, you must first enable them:
1002
1003 no warnings 'experimental::lexical_subs';
1004 use feature 'lexical_subs';
1005 my sub foo { ... }
1006
1007=back
1008
1009=head3 New Warnings
1010
1011=over 4
1012
1013=item *
1014
1015XXX: This needs more detail.
1016
1017Strings with code points over 0xFF may not be mapped into in-memory file
1018handles
1019
1020=item *
1021
1022L<'%s' resolved to '\o{%s}%d'|perldiag/"'%s' resolved to '\o{%s}%d'">
1023
1024=item *
1025
1026L<'Trailing white-space in a charnames alias definition is deprecated'|perldiag/"Trailing white-space in a charnames alias definition is deprecated">
1027
1028=item *
1029
1030L<'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">
1031
1032=item *
1033
1034L<'Passing malformed UTF-8 to "%s" is deprecated'|perldiag/"Passing malformed UTF-8 to "%s" is deprecated">
1035
1036=item *
1037
1038L<Subroutine "&%s" is not available|perldiag/"Subroutine "&%s" is not available">
1039
1040(W closure) During compilation, an inner named subroutine or eval is
1041attempting to capture an outer lexical subroutine that is not currently
1042available. This can happen for one of two reasons. First, the lexical
1043subroutine may be declared in an outer anonymous subroutine that has not
1044yet been created. (Remember that named subs are created at compile time,
1045while anonymous subs are created at run-time.) For example,
1046
1047 sub { my sub a {...} sub f { \&a } }
1048
1049At the time that f is created, it can't capture the current the "a" sub,
1050since the anonymous subroutine hasn't been created yet. Conversely, the
1051following won't give a warning since the anonymous subroutine has by now
1052been created and is live:
1053
1054 sub { my sub a {...} eval 'sub f { \&a }' }->();
1055
1056The second situation is caused by an eval accessing a variable that has
1057gone out of scope, for example,
1058
1059 sub f {
1060 my sub a {...}
1061 sub { eval '\&a' }
1062 }
1063 f()->();
1064
1065Here, when the '\&a' in the eval is being compiled, f() is not currently
1066being executed, so its &a is not available for capture.
1067
1068=item *
1069
1070L<"%s" subroutine &%s masks earlier declaration in same %s|perldiag/"%s" subroutine &%s masks earlier declaration in same %s>
1071
1072(W misc) A "my" or "state" subroutine has been redeclared in the
1073current scope or statement, effectively eliminating all access to
1074the previous instance. This is almost always a typographical error.
1075Note that the earlier subroutine will still exist until the end of
1076the scope or until all closure references to it are destroyed.
1077
1078=item *
1079
1080L<The %s feature is experimental|perldiag/"The %s feature is experimental">
1081
1082(S experimental) This warning is emitted if you enable an experimental
1083feature via C<use feature>. Simply suppress the warning if you want
1084to use the feature, but know that in doing so you are taking the risk
1085of using an experimental feature which may change or be removed in a
1086future Perl version:
1087
1088 no warnings "experimental::lexical_subs";
1089 use feature "lexical_subs";
1090
1091=item *
1092
1093L<sleep(%u) too large|perldiag/"sleep(%u) too large">
1094
1095(W overflow) You called C<sleep> with a number that was larger than it can
1096reliably handle and C<sleep> probably slept for less time than requested.
1097
1098=item *
1099
1100L<Wide character in setenv|perldiag/"Wide character in %s">
1101
1102Attempts to put wide characters into environment variables via C<%ENV> now
1103provoke this warning.
1104
1105=item *
1106
1107"L<Invalid negative number (%s) in chr|perldiag/"Invalid negative number (%s) in chr">"
1108
1109C<chr()> now warns when passed a negative value [perl #83048].
1110
1111=item *
1112
1113"L<Integer overflow in srand|perldiag/"Integer overflow in srand">"
1114
1115C<srand()> now warns when passed a value that doesn't fit in a C<UV> (since the
1116value will be truncated rather than overflowing) [perl #40605].
1117
1118=item *
1119
1120"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">"
1121
1122Running perl with the C<-i> flag now warns if no input files are provided on
1123the command line [perl #113410].
1124
1125=back
1126
1127=head2 Changes to Existing Diagnostics
1128
1129=over 4
1130
1131=item *
1132
1133L<$* is no longer supported|perldiag/"$* is no longer supported">
1134
1135The warning that use of C<$*> and C<$#> is no longer supported is now
1136generated for every location that references them. Previously it would fail
1137to be generated if another variable using the same typeglob was seen first
1138(e.g. C<@*> before C<$*>), and would not be generated for the second and
1139subsequent uses. (It's hard to fix the failure to generate warnings at all
1140without also generating them every time, and warning every time is
1141consistent with the warnings that C<$[> used to generate.)
1142
1143=item *
1144
1145The warnings for C<\b{> and C<\B{> were added. They are a deprecation
1146warning which should be turned off by that category. One should not
1147have to turn off regular regexp warnings as well to get rid of these.
1148
1149=item *
1150
1151L<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>
1152
1153Constant overloading that returns C<undef> results in this error message.
1154For numeric constants, it used to say "Constant(undef)". "undef" has been
1155replaced with the number itself.
1156
1157=item *
1158
1159The error produced when a module cannot be loaded now includes a hint that
1160the module may need to be installed: "Can't locate hopping.pm in @INC (you
1161may need to install the hopping module) (@INC contains: ...)"
1162
1163=item *
1164
1165L<vector argument not supported with alpha versions|perldiag/vector argument not supported with alpha versions>
1166
1167This warning was not suppressable, even with C<no warnings>. Now it is
1168suppressible, and has been moved from the "internal" category to the
1169"printf" category.
1170
1171=item *
1172
1173C<< Can't do {n,m} with n > m in regex; marked by <-- HERE in m/%s/ >>
1174
1175This fatal error has been turned into a warning that reads:
1176
1177L<< Quantifier {n,m} with n > m can't match in regex | perldiag/Quantifier {n,m} with n > m can't match in regex >>
1178
1179(W regexp) Minima should be less than or equal to maxima. If you really want
1180your regexp to match something 0 times, just put {0}.
1181
1182=item *
1183
1184The "Runaway prototype" warning that occurs in bizarre cases has been
1185removed as being unhelpful and inconsistent.
1186
1187=item *
1188
1189The "Not a format reference" error has been removed, as the only case in
1190which it could be triggered was a bug.
1191
1192=item *
1193
1194The "Unable to create sub named %s" error has been removed for the same
1195reason.
1196
1197=item *
1198
1199The 'Can't use "my %s" in sort comparison' error has been downgraded to a
1200warning, '"my %s" used in sort comparison' (with 'state' instead of 'my'
1201for state variables). In addition, the heuristics for guessing whether
1202lexical $a or $b has been misused have been improved to generate fewer
1203false positives. Lexical $a and $b are no longer disallowed if they are
1204outside the sort block. Also, a named unary or list operator inside the
1205sort block no longer causes the $a or $b to be ignored [perl #86136].
1206
1207=back
1208
1209=head1 Utility Changes
1210
1211=head3 L<h2xs>
1212
1213=over 4
1214
1215=item *
1216
1217F<h2xs> no longer produces invalid code for empty defines. [perl #20636]
1218
1219=back
1220
1221=head1 Configuration and Compilation
1222
1223=over 4
1224
1225=item *
1226
1227Added C<useversionedarchname> option to Configure
1228
1229When set, it includes 'api_versionstring' in 'archname'. E.g.
1230x86_64-linux-5.13.6-thread-multi. It is unset by default.
1231
1232This feature was requested by Tim Bunce, who observed that
f105b7be 1233C<INSTALL_BASE> creates a library structure that does not
5ed58cbd
RS
1234differentiate by perl version. Instead, it places architecture
1235specific files in "$install_base/lib/perl5/$archname". This makes
f105b7be 1236it difficult to use a common C<INSTALL_BASE> library path with
5ed58cbd
RS
1237multiple versions of perl.
1238
f105b7be 1239By setting C<-Duseversionedarchname>, the $archname will be
c2959982 1240distinct for architecture I<and> API version, allowing mixed use of
f105b7be 1241C<INSTALL_BASE>.
5ed58cbd
RS
1242
1243=item *
1244
ff772877
RS
1245Add a C<PERL_NO_INLINE_FUNCTIONS> option
1246
f105b7be 1247If C<PERL_NO_INLINE_FUNCTIONS> is defined, don't include "inline.h"
ff772877
RS
1248
1249This permits test code to include the perl headers for definitions without
1250creating a link dependency on the perl library (which may not exist yet).
1251
1252=item *
1253
5ed58cbd
RS
1254Configure will honour the external C<MAILDOMAIN> environment variable, if set.
1255
1256=item *
1257
1258C<installman> no longer ignores the silent option
1259
1260=item *
1261
1262Both C<META.yml> and C<META.json> files are now included in the distribution.
1263
1264=item *
1265
1266F<Configure> will now correctly detect C<isblank()> when compiling with a C++
1267compiler.
1268
1269=item *
1270
1271The pager detection in F<Configure> has been improved to allow responses which
1272specify options after the program name, e.g. B</usr/bin/less -R>, if the user
1273accepts the default value. This helps B<perldoc> when handling ANSI escapes
1274[perl #72156].
1275
1276=back
1277
1278=head1 Testing
1279
1280=over 4
1281
1282=item *
1283
1284The test suite now has a section for tests that require very large amounts
1285of memory. These tests won't run by default; they can be enabled by
1286setting the C<PERL_TEST_MEMORY> environment variable to the number of
1287gibibytes of memory that may be safely used.
1288
1289=back
1290
1291=head1 Platform Support
1292
1293=head2 Discontinued Platforms
1294
1295=over 4
1296
1297=item BeOS
1298
1299BeOS was an operating system for personal computers developed by Be Inc,
1300initially for their BeBox hardware. The OS Haiku was written as an open
1301source replacement for/continuation of BeOS, and its perl port is current and
1302actively maintained.
1303
1304=item UTS Global
1305
1306Support code relating to UTS global has been removed. UTS was a mainframe
1307version of System V created by Amdahl, subsequently sold to UTS Global. The
e612b5a0 1308port has not been touched since before Perl v5.8.0, and UTS Global is now
5ed58cbd
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1309defunct.
1310
1311=item VM/ESA
1312
1313Support for VM/ESA has been removed. The port was tested on 2.3.0, which
1314IBM ended service on in March 2002. 2.4.0 ended service in June 2003, and
1315was superseded by Z/VM. The current version of Z/VM is V6.2.0, and scheduled
1316for end of service on 2015/04/30.
1317
1318=item MPE/IX
1319
1320Support for MPE/IX has been removed.
1321
1322=item EPOC
1323
1324Support code relating to EPOC has been removed. EPOC was a family of
1325operating systems developed by Psion for mobile devices. It was the
1326predecessor of Symbian. The port was last updated in April 2002.
1327
1328=item Rhapsody
1329
1330Support for Rhapsody has been removed.
1331
1332=back
1333
1334=head2 Platform-Specific Notes
1335
1336=head3 AIX
1337
1338Configure now always adds C<-qlanglvl=extc99> to the CC flags on AIX when
1339using xlC. This will make it easier to compile a number of XS-based modules
1340that assume C99 [perl #113778].
1341
1342=head3 clang++
1343
1344There is now a workaround for a compiler bug that prevented compiling
e612b5a0 1345with clang++ since Perl v5.15.7 [perl #112786].
5ed58cbd
RS
1346
1347=head3 C++
1348
1349When compiling the Perl core as C++ (which is only semi-supported), the
1350mathom functions are now compiled as C<extern "C">, to ensure proper
1351binary compatibility. (However, binary compatibility isn't generally
1352guaranteed anyway in the situations where this would matter.)
1353
1354=head3 Darwin
1355
1356Stop hardcoding an alignment on 8 byte boundaries to fix builds using
1357-Dusemorebits.
1358
1359=head3 Haiku
1360
1361Perl should now work out of the box on Haiku R1 Alpha 4.
1362
1363=head3 MidnightBSD
1364
1365C<libc_r> was removed from recent versions of MidnightBSD and older versions
1366work better with C<pthread>. Threading is now enabled using C<pthread> which
1367corrects build errors with threading enabled on 0.4-CURRENT.
1368
1369=head3 Solaris
1370
1371In Configure, avoid running sed commands with flags not supported on Solaris.
1372
1373=head3 VMS
1374
1375=over
1376
1377=item *
1378
1379Where possible, the case of filenames and command-line arguments is now
1380preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
1381C<DECC$ARGV_PARSE_STYLE> at start-up time. The latter only takes effect
1382when extended parse is enabled in the process from which Perl is run.
1383
1384=item *
1385
1386The character set for Extended Filename Syntax (EFS) is now enabled by default
1387on VMS. Among other things, this provides better handling of dots in directory
05f5908f 1388names, multiple dots in filenames, and spaces in filenames. To obtain the old
5ed58cbd
RS
1389behavior, set the logical name C<DECC$EFS_CHARSET> to C<DISABLE>.
1390
1391=item *
1392
05f5908f 1393Fixed linking on builds configured with C<-Dusemymalloc=y>.
5ed58cbd
RS
1394
1395=item *
1396
05f5908f
CB
1397Experimental support for building Perl with the HP C++ compiler is available
1398by configuring with C<-Dusecxx>.
5ed58cbd
RS
1399
1400=item *
1401
1402All C header files from the top-level directory of the distribution are now
1403installed on VMS, providing consistency with a long-standing practice on other
1404platforms. Previously only a subset were installed, which broke non-core
1405extension builds for extensions that depended on the missing include files.
1406
1407=item *
1408
1409Quotes are now removed from the command verb (but not the parameters) for
1410commands spawned via C<system>, backticks, or a piped C<open>. Previously,
1411quotes on the verb were passed through to DCL, which would fail to recognize
1412the command. Also, if the verb is actually a path to an image or command
1413procedure on an ODS-5 volume, quoting it now allows the path to contain spaces.
1414
1415=item *
1416
1417The B<a2p> build has been fixed for the HP C++ compiler on OpenVMS.
1418
1419=back
1420
1421=head3 Win32
1422
1423=over
1424
1425=item *
1426
1427Perl can now be built using Microsoft's Visual C++ 2012 compiler by specifying
1428CCTYPE=MSVC110 (or MSVC110FREE if you are using the free Express edition for
1429Windows Desktop) in F<win32/Makefile>.
1430
1431=item *
1432
f105b7be 1433The option to build without C<USE_SOCKETS_AS_HANDLES> has been removed.
5ed58cbd
RS
1434
1435=item *
1436
1437Fixed a problem where perl could crash while cleaning up threads (including the
1438main thread) in threaded debugging builds on Win32 and possibly other platforms
1439[perl #114496].
1440
1441=item *
1442
1443A rare race condition that would lead to L<sleep|perlfunc/sleep> taking more
1444time than requested, and possibly even hanging, has been fixed [perl #33096].
1445
1446=item *
1447
1448C<link> on Win32 now attempts to set C<$!> to more appropriate values
1449based on the Win32 API error code. [perl #112272]
1450
1451Perl no longer mangles the environment block, e.g. when launching a new
1452sub-process, when the environment contains non-ASCII characters. Known
1453problems still remain, however, when the environment contains characters
1454outside of the current ANSI codepage (e.g. see the item about Unicode in
1455C<%ENV> in L<http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod>).
1456[perl #113536]
1457
1458=item *
1459
1460Building perl with some Windows compilers used to fail due to a problem
1461with miniperl's C<glob> operator (which uses the C<perlglob> program)
1462deleting the PATH environment variable [perl #113798].
1463
1464=item *
1465
f105b7be 1466A new makefile option, C<USE_64_BIT_INT>, has been added to the Windows
5ed58cbd
RS
1467makefiles. Set this to "define" when building a 32-bit perl if you want
1468it to use 64-bit integers.
1469
1470Machine code size reductions, already made to the DLLs of XS modules in
e612b5a0 1471Perl v5.17.2, have now been extended to the perl DLL itself.
5ed58cbd 1472
e612b5a0 1473Building with VC++ 6.0 was inadvertently broken in Perl v5.17.2 but has
5ed58cbd
RS
1474now been fixed again.
1475
1476=back
1477
1478=head3 WinCE
1479
1480Building on WinCE is now possible once again, although more work is required
1481to fully restore a clean build.
1482
1483=head1 Internal Changes
1484
1485=over
1486
1487=item *
1488
4263dd11 1489Synonyms for the misleadingly named C<av_len()> have been created:
5ed58cbd
RS
1490C<av_top_index()> and C<av_tindex>. All three of these return the
1491number of the highest index in the array, not the number of elements it
1492contains.
1493
1494=item *
1495
1496SvUPGRADE() is no longer an expression. Originally this macro (and its
1497underlying function, sv_upgrade()) were documented as boolean, although
1498in reality they always croaked on error and never returned false. In 2005
1499the documentation was updated to specify a void return value, but
1500SvUPGRADE() was left always returning 1 for backwards compatibility. This
1501has now been removed, and SvUPGRADE() is now a statement with no return
1502value.
1503
1504So this is now a syntax error:
1505
1506 if (!SvUPGRADE(sv)) { croak(...); }
1507
1508If you have code like that, simply replace it with
1509
1510 SvUPGRADE(sv);
1511
1512or to to avoid compiler warnings with older perls, possibly
1513
1514 (void)SvUPGRADE(sv);
1515
1516=item *
1517
1518Perl has a new copy-on-write mechanism that allows any SvPOK scalar to be
1519upgraded to a copy-on-write scalar. A reference count on the string buffer
1520is stored in the string buffer itself.
1521
1522This breaks a few XS modules by allowing copy-on-write scalars to go
1523through code paths that never encountered them before.
1524
1525This behaviour can still be disabled by running F<Configure> with
1526B<-Accflags=-DPERL_NO_COW>. This option will probably be removed in Perl
15275.20.
1528
1529=item *
1530
1531Copy-on-write no longer uses the SvFAKE and SvREADONLY flags. Hence,
1532SvREADONLY indicates a true read-only SV.
1533
1534Use the SvIsCOW macro (as before) to identify a copy-on-write scalar.
1535
1536=item *
1537
f105b7be 1538C<PL_glob_index> is gone.
5ed58cbd
RS
1539
1540=item *
1541
1542The private Perl_croak_no_modify has had its context parameter removed. It is
1543now has a void prototype. Users of the public API croak_no_modify remain
1544unaffected.
1545
1546=item *
1547
1548Copy-on-write (shared hash key) scalars are no longer marked read-only.
1549C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
1550true.
1551
1552=item *
1553
1554A new op type, C<OP_PADRANGE> has been introduced. The perl peephole
1555optimiser will, where possible, substitute a single padrange op for a
1556pushmark followed by one or more pad ops, and possibly also skipping list
1557and nextstate ops. In addition, the op can carry out the tasks associated
f105b7be 1558with the RHS of a C<< my(...) = @_ >> assignment, so those ops may be optimised
5ed58cbd
RS
1559away too.
1560
1561=item *
1562
1563Case-insensitive matching inside a [bracketed] character class with a
1564multi-character fold no longer excludes one of the possibilities in the
1565circumstances that it used to. [perl #89774].
1566
1567=item *
1568
1569C<PL_formfeed> has been removed.
1570
1571=item *
1572
1573The regular expression engine no longer reads one byte past the end of the
1574target string. While for all internally well-formed scalars this should
1575never have been a problem, this change facilitates clever tricks with
1576string buffers in CPAN modules. [perl #73542]
1577
1578=item *
1579
1580Inside a BEGIN block, C<PL_compcv> now points to the currently-compiling
1581subroutine, rather than the BEGIN block itself.
1582
1583=item *
1584
1585C<mg_length> has been deprecated.
1586
1587=item *
1588
1589C<sv_len> now always returns a byte count and C<sv_len_utf8> a character
1590count. Previously, C<sv_len> and C<sv_len_utf8> were both buggy and would
1591sometimes returns bytes and sometimes characters. C<sv_len_utf8> no longer
be12dd22 1592assumes that its argument is in UTF-8. Neither of these creates UTF-8 caches
5ed58cbd
RS
1593for tied or overloaded values or for non-PVs any more.
1594
1595=item *
1596
1597C<sv_mortalcopy> now copies string buffers of shared hash key scalars when
1598called from XS modules [perl #79824].
1599
1600=item *
1601
1602C<RXf_SPLIT> and C<RXf_SKIPWHITE> are no longer used. They are now
1603#defined as 0.
1604
1605=item *
1606
1607The new C<RXf_MODIFIES_VARS> flag can be set by custom regular expression
1608engines to indicate that the execution of the regular expression may cause
1609variables to be modified. This lets C<s///> know to skip certain
1610optimisations. Perl's own regular expression engine sets this flag for the
1611special backtracking verbs that set $REGMARK and $REGERROR.
1612
1613=item *
1614
1615The APIs for accessing lexical pads have changed considerably.
1616
1617C<PADLIST>s are now longer C<AV>s, but their own type instead.
1618C<PADLIST>s now contain a C<PAD> and a C<PADNAMELIST> of C<PADNAME>s,
1619rather than C<AV>s for the pad and the list of pad names. C<PAD>s,
1620C<PADNAMELIST>s, and C<PADNAME>s are to be accessed as such through the
1621newly added pad API instead of the plain C<AV> and C<SV> APIs. See
1622L<perlapi> for details.
1623
1624=item *
1625
1626In the regex API, the numbered capture callbacks are passed an index
1627indicating what match variable is being accessed. There are special
1628index values for the C<$`, $&, $&> variables. Previously the same three
1629values were used to retrieve C<${^PREMATCH}, ${^MATCH}, ${^POSTMATCH}>
1630too, but these have now been assigned three separate values. See
1631L<perlreapi/Numbered capture callbacks>.
1632
1633=item *
1634
1635C<PL_sawampersand> was previously a boolean indicating that any of
1636C<$`, $&, $&> had been seen; it now contains three one-bit flags
1637indicating the presence of each of the variables individually.
1638
1639=item *
1640
1641The C<CV *> typemap entry now supports C<&{}> overloading and typeglobs,
1642just like C<&{...}> [perl #96872].
1643
1644=item *
1645
1646The C<SVf_AMAGIC> flag to indicate overloading is now on the stash, not the
1647object. It is now set automatically whenever a method or @ISA changes, so
1648its meaning has changed, too. It now means "potentially overloaded". When
1649the overload table is calculated, the flag is automatically turned off if
1650there is no overloading, so there should be no noticeable slowdown.
1651
1652The staleness of the overload tables is now checked when overload methods
1653are invoked, rather than during C<bless>.
1654
1655"A" magic is gone. The changes to the handling of the C<SVf_AMAGIC> flag
1656eliminate the need for it.
1657
1658C<PL_amagic_generation> has been removed as no longer necessary. For XS
1659modules, it is now a macro alias to C<PL_na>.
1660
1661The fallback overload setting is now stored in a stash entry separate from
1662overloadedness itself.
1663
1664=item *
1665
1666The character-processing code has been cleaned up in places. The changes
1667should be operationally invisible.
1668
1669=item *
1670
e612b5a0 1671The C<study> function was made a no-op in v5.16. It was simply disabled via
5ed58cbd
RS
1672a C<return> statement; the code was left in place. Now the code supporting
1673what C<study> used to do has been removed.
1674
1675=item *
1676
1677Under threaded perls, there is no longer a separate PV allocated for every
1678COP to store its package name (C<< cop->stashpv >>). Instead, there is an
1679offset (C<< cop->stashoff >>) into the new C<PL_stashpad> array, which
1680holds stash pointers.
1681
1682=item *
1683
1684In the pluggable regex API, the C<regexp_engine> struct has acquired a new
1685field C<op_comp>, which is currently just for perl's internal use, and
f105b7be 1686should be initialized to NULL by other regex plugin modules.
5ed58cbd
RS
1687
1688=item *
1689
7779650e 1690A new function C<alloccopstash> has been added to the API, but is considered
5ed58cbd
RS
1691experimental. See L<perlapi>.
1692
1693=item *
1694
1695Perl used to implement get magic in a way that would sometimes hide bugs in
4263dd11 1696code that could call mg_get() too many times on magical values. This hiding of
5ed58cbd
RS
1697errors no longer occurs, so long-standing bugs may become visible now. If
1698you see magic-related errors in XS code, check to make sure it, together
1699with the Perl API functions it uses, calls mg_get() only once on SvGMAGICAL()
1700values.
1701
1702=item *
1703
1704OP allocation for CVs now uses a slab allocator. This simplifies
1705memory management for OPs allocated to a CV, so cleaning up after a
1706compilation error is simpler and safer [perl #111462][perl #112312].
1707
1708=item *
1709
f105b7be 1710C<PERL_DEBUG_READONLY_OPS> has been rewritten to work with the new slab
5ed58cbd
RS
1711allocator, allowing it to catch more violations than before.
1712
1713=item *
1714
f105b7be
KE
1715The old slab allocator for ops, which was only enabled for C<PERL_IMPLICIT_SYS>
1716and C<PERL_DEBUG_READONLY_OPS>, has been retired.
5ed58cbd
RS
1717
1718=back
1719
1720=head1 Selected Bug Fixes
1721
1722=over 4
1723
1724=item *
1725
1726Here-doc terminators no longer require a terminating newline character when
1727they occur at the end of a file. This was already the case at the end of a
1728string eval [perl #65838].
1729
1730=item *
1731
f105b7be 1732C<-DPERL_GLOBAL_STRUCT> builds now free the global struct B<after>
5ed58cbd
RS
1733they've finished using it.
1734
1735=item *
1736
1737A trailing '/' on a path in @INC will no longer have an additional '/'
1738appended.
1739
1740=item *
1741
1742The C<:crlf> layer now works when unread data doesn't fit into its own
1743buffer. [perl #112244].
1744
1745=item *
1746
1747C<ungetc()> now handles UTF-8 encoded data. [perl #116322].
1748
1749=item *
1750
1751A bug in the core typemap caused any C types that map to the T_BOOL core
1752typemap entry to not be set, updated, or modified when the T_BOOL variable was
1753used in an OUTPUT: section with an exception for RETVAL. T_BOOL in an INPUT:
1754section was not affected. Using a T_BOOL return type for an XSUB (RETVAL)
1755was not affected. A side effect of fixing this bug is, if a T_BOOL is specified
1756in the OUTPUT: section (which previous did nothing to the SV), and a read only
1757SV (literal) is passed to the XSUB, croaks like "Modification of a read-only
1758value attempted" will happen. [perl #115796]
1759
1760=item *
1761
1762On many platforms, providing a directory name as the script name caused perl
1763to do nothing and report success. It should now universally report an error
1764and exit nonzero. [perl #61362]
1765
1766=item *
1767
1768C<sort {undef} ...> under fatal warnings no longer crashes. It had
e612b5a0 1769begun crashing in Perl v5.16.
5ed58cbd
RS
1770
1771=item *
1772
1773Stashes blessed into each other
1774(C<bless \%Foo::, 'Bar'; bless \%Bar::, 'Foo'>) no longer result in double
e612b5a0 1775frees. This bug started happening in Perl v5.16.
5ed58cbd
RS
1776
1777=item *
1778
1779Numerous memory leaks have been fixed, mostly involving fatal warnings and
1780syntax errors.
1781
1782=item *
1783
1784Some failed regular expression matches such as C<'f' =~ /../g> were not
1785resetting C<pos>. Also, "match-once" patterns (C<m?...?g>) failed to reset
1786it, too, when invoked a second time [perl #23180].
1787
1788=item *
1789
1790Accessing C<$&> after a pattern match now works if it had not been seen
1791before the match. I.e., this applies to C<${'&'}> (under C<no strict>) and
1792C<eval '$&'>. The same applies to C<$'> and C<$`> [perl #4289].
1793
1794=item *
1795
1796Several bugs involving C<local *ISA> and C<local *Foo::> causing stale
1797MRO caches have been fixed.
1798
1799=item *
1800
1801Defining a subroutine when its typeglob has been aliased no longer results
e612b5a0 1802in stale method caches. This bug was introduced in Perl v5.10.
5ed58cbd
RS
1803
1804=item *
1805
1806Localising a typeglob containing a subroutine when the typeglob's package
1807has been deleted from its parent stash no longer produces an error. This
e612b5a0 1808bug was introduced in Perl v5.14.
5ed58cbd
RS
1809
1810=item *
1811
1812Under some circumstances, C<local *method=...> would fail to reset method
1813caches upon scope exit.
1814
1815=item *
1816
1817C</[.foo.]/> is no longer an error, but produces a warning (as before) and
1818is treated as C</[.fo]/> [perl #115818].
1819
1820=item *
1821
1822C<goto $tied_var> now calls FETCH before deciding what type of goto
1823(subroutine or label) this is.
1824
1825=item *
1826
1827Renaming packages through glob assignment
1828(C<*Foo:: = *Bar::; *Bar:: = *Baz::>) in combination with C<m?...?> and
1829C<reset> no longer makes threaded builds crash.
1830
1831=item *
1832
1833A number of bugs related to assigning a list to hash have been fixed. Many of
1834these involve lists with repeated keys like C<(1, 1, 1, 1)>.
1835
1836=over 4
1837
1838=item *
1839
1840The expression C<scalar(%h = (1, 1, 1, 1))> now returns C<4>, not C<2>.
1841
1842=item *
1843
1844The return value of C<%h = (1, 1, 1)> in list context was wrong. Previously
1845this would return C<(1, undef, 1)>, now it returns C<(1, undef)>.
1846
1847=item *
1848
1849Perl now issues the same warning on C<($s, %h) = (1, {})> as it does for
1850C<(%h) = ({})>, "Reference found where even-sized list expected".
1851
1852=item *
1853
1854A number of additional edge cases in list assignment to hashes were
1855corrected. For more details see commit 23b7025ebc.
1856
1857=back
1858
1859=item *
1860
1861Attributes applied to lexical variables no longer leak memory.
1862[perl #114764]
1863
1864=item *
1865
1866C<dump>, C<goto>, C<last>, C<next>, C<redo> or C<require> followed by a
1867bareword (or version) and then an infix operator is no longer a syntax
1868error. It used to be for those infix operators (like C<+>) that have a
1869different meaning where a term is expected. [perl #105924]
1870
1871=item *
1872
1873C<require a::b . 1> and C<require a::b + 1> no longer produce erroneous
1874ambiguity warnings. [perl #107002]
1875
1876=item *
1877
1878Class method calls are now allowed on any string, and not just strings
1879beginning with an alphanumeric character. [perl #105922]
1880
1881=item *
1882
1883An empty pattern created with C<qr//> used in C<m///> no longer triggers
1884the "empty pattern reuses last pattern" behaviour. [perl #96230]
1885
1886=item *
1887
1888Tying a hash during iteration no longer results in a memory leak.
1889
1890=item *
1891
1892Freeing a tied hash during iteration no longer results in a memory leak.
1893
1894=item *
1895
1896List assignment to a tied array or hash that dies on STORE no longer
1897results in a memory leak.
1898
1899=item *
1900
1901If the hint hash (C<%^H>) is tied, compile-time scope entry (which copies
1902the hint hash) no longer leaks memory if FETCH dies. [perl #107000]
1903
1904=item *
1905
1906Constant folding no longer inappropriately triggers the special
1907C<split " "> behaviour. [perl #94490]
1908
1909=item *
1910
1911C<defined scalar(@array)>, C<defined do { &foo }>, and similar constructs
1912now treat the argument to C<defined> as a simple scalar. [perl #97466]
1913
1914=item *
1915
1916Running a custom debugging that defines no C<*DB::DB> glob or provides a
1917subroutine stub for C<&DB::DB> no longer results in a crash, but an error
1918instead. [perl #114990]
1919
1920=item *
1921
1922C<reset ""> now matches its documentation. C<reset> only resets C<m?...?>
1923patterns when called with no argument. An empty string for an argument now
1924does nothing. (It used to be treated as no argument.) [perl #97958]
1925
1926=item *
1927
1928C<printf> with an argument returning an empty list no longer reads past the
1929end of the stack, resulting in erratic behaviour. [perl #77094]
1930
1931=item *
1932
1933C<--subname> no longer produces erroneous ambiguity warnings.
1934[perl #77240]
1935
1936=item *
1937
1938C<v10> is now allowed as a label or package name. This was inadvertently
e612b5a0 1939broken when v-strings were added in Perl v5.6. [perl #56880]
5ed58cbd
RS
1940
1941=item *
1942
1943C<length>, C<pos>, C<substr> and C<sprintf> could be confused by ties,
1944overloading, references and typeglobs if the stringification of such
be12dd22 1945changed the internal representation to or from UTF-8. [perl #114410]
5ed58cbd
RS
1946
1947=item *
1948
1949utf8::encode now calls FETCH and STORE on tied variables. utf8::decode now
1950calls STORE (it was already calling FETCH).
1951
1952=item *
1953
1954C<$tied =~ s/$non_utf8/$utf8/> no longer loops infinitely if the tied
1955variable returns a Latin-1 string, shared hash key scalar, or reference or
2ae351f8 1956typeglob that stringifies as ASCII or Latin-1. This was a regression from
e612b5a0 1957v5.12.
5ed58cbd
RS
1958
1959=item *
1960
1961C<s///> without /e is now better at detecting when it needs to forego
1962certain optimisations, fixing some buggy cases:
1963
1964=over
1965
1966=item *
1967
1968Match variables in certain constructs (C<&&>, C<||>, C<..> and others) in
1969the replacement part; e.g., C<s/(.)/$l{$a||$1}/g>. [perl #26986]
1970
1971=item *
1972
1973Aliases to match variables in the replacement.
1974
1975=item *
1976
1977C<$REGERROR> or C<$REGMARK> in the replacement. [perl #49190]
1978
1979=item *
1980
1981An empty pattern (C<s//$foo/>) that causes the last-successful pattern to
1982be used, when that pattern contains code blocks that modify the variables
1983in the replacement.
1984
1985=back
1986
1987=item *
1988
1989The taintedness of the replacement string no longer affects the taintedness
1990of the return value of C<s///e>.
1991
1992=item *
1993
1994The C<$|> autoflush variable is created on-the-fly when needed. If this
1995happened (e.g., if it was mentioned in a module or eval) when the
1996currently-selected filehandle was a typeglob with an empty IO slot, it used
1997to crash. [perl #115206]
1998
1999=item *
2000
2001Line numbers at the end of a string eval are no longer off by one.
2002[perl #114658]
2003
2004=item *
2005
2006@INC filters (subroutines returned by subroutines in @INC) that set $_ to a
2007copy-on-write scalar no longer cause the parser to modify that string
2008buffer in place.
2009
2010=item *
2011
2012C<length($object)> no longer returns the undefined value if the object has
2013string overloading that returns undef. [perl #115260]
2014
2015=item *
2016
2017The use of C<PL_stashcache>, the stash name lookup cache for method calls, has
2018been restored,
2019
2020Commit da6b625f78f5f133 in August 2011 inadvertently broke the code that looks
2021up values in C<PL_stashcache>. As it's a only cache, quite correctly everything
2022carried on working without it.
2023
2024=item *
2025
e612b5a0 2026The error "Can't localize through a reference" had disappeared in v5.16.0
5ed58cbd 2027when C<local %$ref> appeared on the last line of an lvalue subroutine.
e612b5a0 2028This error disappeared for C<\local %$ref> in perl v5.8.1. It has now
5ed58cbd
RS
2029been restored.
2030
2031=item *
2032
2033The parsing of here-docs has been improved significantly, fixing several
2034parsing bugs and crashes and one memory leak, and correcting wrong
2035subsequent line numbers under certain conditions.
2036
2037=item *
2038
2039Inside an eval, the error message for an unterminated here-doc no longer
2040has a newline in the middle of it [perl #70836].
2041
2042=item *
2043
2044A substitution inside a substitution pattern (C<s/${s|||}//>) no longer
2045confuses the parser.
2046
2047=item *
2048
2049It may be an odd place to allow comments, but C<s//"" # hello/e> has
2050always worked, I<unless> there happens to be a null character before the
2051first #. Now it works even in the presence of nulls.
2052
2053=item *
2054
2055An invalid range in C<tr///> or C<y///> no longer results in a memory leak.
2056
2057=item *
2058
2059String eval no longer treats a semicolon-delimited quote-like operator at
2060the very end (C<eval 'q;;'>) as a syntax error.
2061
2062=item *
2063
2064C<< warn {$_ => 1} + 1 >> is no longer a syntax error. The parser used to
2065get confused with certain list operators followed by an anonymous hash and
2066then an infix operator that shares its form with a unary operator.
2067
2068=item *
2069
2070C<(caller $n)[6]> (which gives the text of the eval) used to return the
2071actual parser buffer. Modifying it could result in crashes. Now it always
2072returns a copy. The string returned no longer has "\n;" tacked on to the
2073end. The returned text also includes here-doc bodies, which used to be
2074omitted.
2075
2076=item *
2077
be12dd22
RS
2078Reset the UTF-8 position cache when accessing magical variables to avoid the
2079string buffer and the UTF-8 position cache getting out of sync
5ed58cbd
RS
2080[perl #114410].
2081
2082=item *
2083
be12dd22
RS
2084Various cases of get magic being called twice for magical UTF-8
2085strings have been fixed.
5ed58cbd
RS
2086
2087=item *
2088
2089This code (when not in the presence of C<$&> etc)
2090
2091 $_ = 'x' x 1_000_000;
2092 1 while /(.)/;
2093
2094used to skip the buffer copy for performance reasons, but suffered from C<$1>
2095etc changing if the original string changed. That's now been fixed.
2096
2097=item *
2098
2099Perl doesn't use PerlIO anymore to report out of memory messages, as PerlIO
2100might attempt to allocate more memory.
2101
2102=item *
2103
2104In a regular expression, if something is quantified with C<{n,m}> where
2105C<S<n E<gt> m>>, it can't possibly match. Previously this was a fatal
2106error, but now is merely a warning (and that something won't match).
2107[perl #82954].
2108
2109=item *
2110
2111It used to be possible for formats defined in subroutines that have
2112subsequently been undefined and redefined to close over variables in the
2113wrong pad (the newly-defined enclosing sub), resulting in crashes or
2114"Bizarre copy" errors.
2115
2116=item *
2117
2118Redefinition of XSUBs at run time could produce warnings with the wrong
2119line number.
2120
2121=item *
2122
2123The %vd sprintf format does not support version objects for alpha versions.
2124It used to output the format itself (%vd) when passed an alpha version, and
2125also emit an "Invalid conversion in printf" warning. It no longer does,
2126but produces the empty string in the output. It also no longer leaks
2127memory in this case.
2128
2129=item *
2130
2131C<< $obj->SUPER::method >> calls in the main package could fail if the
2132SUPER package had already been accessed by other means.
2133
2134=item *
2135
f105b7be 2136Stash aliasing (C<< *foo:: = *bar:: >>) no longer causes SUPER calls to ignore
5ed58cbd
RS
2137changes to methods or @ISA or use the wrong package.
2138
2139=item *
2140
2141Method calls on packages whose names end in ::SUPER are no longer treated
2142as SUPER method calls, resulting in failure to find the method.
2143Furthermore, defining subroutines in such packages no longer causes them to
2144be found by SUPER method calls on the containing package [perl #114924].
2145
2146=item *
2147
2148C<\w> now matches the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D
2149(ZERO WIDTH JOINER). C<\W> no longer matches these. This change is because
2150Unicode corrected their definition of what C<\w> should match.
2151
2152=item *
2153
2154C<dump LABEL> no longer leaks its label.
2155
2156=item *
2157
2158Constant folding no longer changes the behaviour of functions like C<stat()>
2159and C<truncate()> that can take either filenames or handles.
2160C<stat 1 ? foo : bar> nows treats its argument as a file name (since it is an
2161arbitrary expression), rather than the handle "foo".
2162
2163=item *
2164
2165C<truncate FOO, $len> no longer falls back to treating "FOO" as a file name if
e612b5a0 2166the filehandle has been deleted. This was broken in Perl v5.16.0.
5ed58cbd
RS
2167
2168=item *
2169
2170Subroutine redefinitions after sub-to-glob and glob-to-glob assignments no
2171longer cause double frees or panic messages.
2172
2173=item *
2174
2175C<s///> now turns vstrings into plain strings when performing a substitution,
2176even if the resulting string is the same (C<s/a/a/>).
2177
2178=item *
2179
2180Prototype mismatch warnings no longer erroneously treat constant subs as having
2181no prototype when they actually have "".
2182
2183=item *
2184
2185Constant subroutines and forward declarations no longer prevent prototype
2186mismatch warnings from omitting the sub name.
2187
2188=item *
2189
2190C<undef> on a subroutine now clears call checkers.
2191
2192=item *
2193
e612b5a0 2194The C<ref> operator started leaking memory on blessed objects in Perl v5.16.0.
5ed58cbd
RS
2195This has been fixed [perl #114340].
2196
2197=item *
2198
2199C<use> no longer tries to parse its arguments as a statement, making
2200C<use constant { () };> a syntax error [perl #114222].
2201
2202=item *
2203
2204On debugging builds, "uninitialized" warnings inside formats no longer cause
2205assertion failures.
2206
2207=item *
2208
2209On debugging builds, subroutines nested inside formats no longer cause
2210assertion failures [perl #78550].
2211
2212=item *
2213
2214Formats and C<use> statements are now permitted inside formats.
2215
2216=item *
2217
2218C<print $x> and C<sub { print $x }-E<gt>()> now always produce the same output.
2219It was possible for the latter to refuse to close over $x if the variable was
2220not active; e.g., if it was defined outside a currently-running named
2221subroutine.
2222
2223=item *
2224
2225Similarly, C<print $x> and C<print eval '$x'> now produce the same output.
2226This also allows "my $x if 0" variables to be seen in the debugger [perl
2227#114018].
2228
2229=item *
2230
2231Formats called recursively no longer stomp on their own lexical variables, but
2232each recursive call has its own set of lexicals.
2233
2234=item *
2235
2236Attempting to free an active format or the handle associated with it no longer
2237results in a crash.
2238
2239=item *
2240
2241Format parsing no longer gets confused by braces, semicolons and low-precedence
2242operators. It used to be possible to use braces as format delimiters (instead
2243of C<=> and C<.>), but only sometimes. Semicolons and low-precedence operators
2244in format argument lines no longer confuse the parser into ignoring the line's
2245return value. In format argument lines, braces can now be used for anonymous
2246hashes, instead of being treated always as C<do> blocks.
2247
2248=item *
2249
2250Formats can now be nested inside code blocks in regular expressions and other
2251quoted constructs (C</(?{...})/> and C<qq/${...}/>) [perl #114040].
2252
2253=item *
2254
2255Formats are no longer created after compilation errors.
2256
2257=item *
2258
2259Under debugging builds, the B<-DA> command line option started crashing in Perl
e612b5a0 2260v5.16.0. It has been fixed [perl #114368].
5ed58cbd
RS
2261
2262=item *
2263
2264A potential deadlock scenario involving the premature termination of a pseudo-
2265forked child in a Windows build with ithreads enabled has been fixed. This
2266resolves the common problem of the F<t/op/fork.t> test hanging on Windows [perl
2267#88840].
2268
2269=item *
2270
5ed58cbd
RS
2271The code which generates errors from C<require()> could potentially read one or
2272two bytes before the start of the filename for filenames less than three bytes
2273long and ending C</\.p?\z/>. This has now been fixed. Note that it could
2274never have happened with module names given to C<use()> or C<require()> anyway.
2275
2276=item *
2277
2278The handling of pathnames of modules given to C<require()> has been made
2279thread-safe on VMS.
2280
2281=item *
2282
d85cd26b
RS
2283Non-blocking sockets have been fixed on VMS.
2284
2285=item *
2286
5ed58cbd
RS
2287A bug in the compilation of a C</(?{})/> expression which affected the TryCatch
2288test suite has been fixed [perl #114242].
2289
2290=item *
2291
2292Pod can now be nested in code inside a quoted construct outside of a string
2293eval. This used to work only within string evals [perl #114040].
2294
2295=item *
2296
2297C<goto ''> now looks for an empty label, producing the "goto must have
2298label" error message, instead of exiting the program [perl #111794].
2299
2300=item *
2301
2302C<goto "\0"> now dies with "Can't find label" instead of "goto must have
2303label".
2304
2305=item *
2306
2307The C function C<hv_store> used to result in crashes when used on C<%^H>
2308[perl #111000].
2309
2310=item *
2311
2312A call checker attached to a closure prototype via C<cv_set_call_checker>
2313is now copied to closures cloned from it. So C<cv_set_call_checker> now
2314works inside an attribute handler for a closure.
2315
2316=item *
2317
2318Writing to C<$^N> used to have no effect. Now it croaks with "Modification
2319of a read-only value" by default, but that can be overridden by a custom
2320regular expression engine, as with C<$1> [perl #112184].
2321
2322=item *
2323
2324C<undef> on a control character glob (C<undef *^H>) no longer emits an
2325erroneous warning about ambiguity [perl #112456].
2326
2327=item *
2328
2329For efficiency's sake, many operators and built-in functions return the
2330same scalar each time. Lvalue subroutines and subroutines in the CORE::
2331namespace were allowing this implementation detail to leak through.
2332C<print &CORE::uc("a"), &CORE::uc("b")> used to print "BB". The same thing
2333would happen with an lvalue subroutine returning the return value of C<uc>.
2334Now the value is copied in such cases.
2335
2336=item *
2337
2338C<method {}> syntax with an empty block or a block returning an empty list
2339used to crash or use some random value left on the stack as its invocant.
2340Now it produces an error.
2341
2342=item *
2343
2344C<vec> now works with extremely large offsets (E<gt>2 GB) [perl #111730].
2345
2346=item *
2347
2348Changes to overload settings now take effect immediately, as do changes to
2349inheritance that affect overloading. They used to take effect only after
2350C<bless>.
2351
2352Objects that were created before a class had any overloading used to remain
2353non-overloaded even if the class gained overloading through C<use overload>
2354or @ISA changes, and even after C<bless>. This has been fixed
2355[perl #112708].
2356
2357=item *
2358
2359Classes with overloading can now inherit fallback values.
2360
2361=item *
2362
2363Overloading was not respecting a fallback value of 0 if there were
2364overloaded objects on both sides of an assignment operator like C<+=>
2365[perl #111856].
2366
2367=item *
2368
2369C<pos> now croaks with hash and array arguments, instead of producing
2370erroneous warnings.
2371
2372=item *
2373
2374C<while(each %h)> now implies C<while(defined($_ = each %h))>, like
2375C<readline> and C<readdir>.
2376
2377=item *
2378
2379Subs in the CORE:: namespace no longer crash after C<undef *_> when called
2380with no argument list (C<&CORE::time> with no parentheses).
2381
2382=item *
2383
2384C<unpack> no longer produces the "'/' must follow a numeric type in unpack"
2385error when it is the data that are at fault [perl #60204].
2386
2387=item *
2388
2389C<join> and C<"@array"> now call FETCH only once on a tied C<$">
2390[perl #8931].
2391
2392=item *
2393
2394Some subroutine calls generated by compiling core ops affected by a
2395C<CORE::GLOBAL> override had op checking performed twice. The checking
2396is always idempotent for pure Perl code, but the double checking can
2397matter when custom call checkers are involved.
2398
2399=item *
2400
2401A race condition used to exist around fork that could cause a signal sent to
2402the parent to be handled by both parent and child. Signals are now blocked
2403briefly around fork to prevent this from happening [perl #82580].
2404
2405=item *
2406
2407The implementation of code blocks in regular expressions, such as C<(?{})>
2408and C<(??{})>, has been heavily reworked to eliminate a whole slew of bugs.
2409The main user-visible changes are:
2410
2411=over 4
2412
2413=item *
2414
2415Code blocks within patterns are now parsed in the same pass as the
2416surrounding code; in particular it is no longer necessary to have balanced
2417braces: this now works:
2418
2419 /(?{ $x='{' })/
2420
2421This means that this error message is no longer generated:
2422
2423 Sequence (?{...}) not terminated or not {}-balanced in regex
2424
2425but a new error may be seen:
2426
2427 Sequence (?{...}) not terminated with ')'
2428
2429In addition, literal code blocks within run-time patterns are only
2430compiled once, at perl compile-time:
2431
2432 for my $p (...) {
2433 # this 'FOO' block of code is compiled once,
2434 # at the same time as the surrounding 'for' loop
2435 /$p{(?{FOO;})/;
2436 }
2437
2438=item *
2439
2440Lexical variables are now sane as regards scope, recursion and closure
2441behavior. In particular, C</A(?{B})C/> behaves (from a closure viewpoint)
2442exactly like C</A/ && do { B } && /C/>, while C<qr/A(?{B})C/> is like
2443C<sub {/A/ && do { B } && /C/}>. So this code now works how you might
2444expect, creating three regexes that match 0, 1, and 2:
2445
2446 for my $i (0..2) {
2447 push @r, qr/^(??{$i})$/;
2448 }
2449 "1" =~ $r[1]; # matches
2450
2451=item *
2452
2453The C<use re 'eval'> pragma is now only required for code blocks defined
2454at runtime; in particular in the following, the text of the C<$r> pattern is
2455still interpolated into the new pattern and recompiled, but the individual
2456compiled code-blocks within C<$r> are reused rather than being recompiled,
2457and C<use re 'eval'> isn't needed any more:
2458
2459 my $r = qr/abc(?{....})def/;
2460 /xyz$r/;
2461
2462=item *
2463
2464Flow control operators no longer crash. Each code block runs in a new
2465dynamic scope, so C<next> etc. will not see
2466any enclosing loops. C<return> returns a value
2467from the code block, not from any enclosing subroutine.
2468
2469=item *
2470
2471Perl normally caches the compilation of run-time patterns, and doesn't
2472recompile if the pattern hasn't changed, but this is now disabled if
2473required for the correct behavior of closures. For example:
2474
2475 my $code = '(??{$x})';
2476 for my $x (1..3) {
2477 # recompile to see fresh value of $x each time
2478 $x =~ /$code/;
2479 }
2480
2481=item *
2482
2483The C</msix> and C<(?msix)> etc. flags are now propagated into the return
2484value from C<(??{})>; this now works:
2485
2486 "AB" =~ /a(??{'b'})/i;
2487
2488=item *
2489
2490Warnings and errors will appear to come from the surrounding code (or for
2491run-time code blocks, from an eval) rather than from an C<re_eval>:
2492
2493 use re 'eval'; $c = '(?{ warn "foo" })'; /$c/;
2494 /(?{ warn "foo" })/;
2495
2496formerly gave:
2497
2498 foo at (re_eval 1) line 1.
2499 foo at (re_eval 2) line 1.
2500
2501and now gives:
2502
2503 foo at (eval 1) line 1.
2504 foo at /some/prog line 2.
2505
2506=back
2507
2508=item *
2509
2e7bc647
KW
2510Perl now can be recompiled to use any Unicode version. In v5.16, it
2511worked on Unicodes 6.0 and 6.1, but there were various bugs if earlier
2512releases were used; the older the release the more problems.
5ed58cbd
RS
2513
2514=item *
2515
2516C<vec> no longer produces "uninitialized" warnings in lvalue context
2517[perl #9423].
2518
2519=item *
2520
2521An optimization involving fixed strings in regular expressions could cause
2522a severe performance penalty in edge cases. This has been fixed
2523[perl #76546].
2524
2525=item *
2526
2527In certain cases, including empty subpatterns within a regular expression (such
2528as C<(?:)> or C<(?:|)>) could disable some optimizations. This has been fixed.
2529
2530=item *
2531
2532The "Can't find an opnumber" message that C<prototype> produces when passed
2533a string like "CORE::nonexistent_keyword" now passes UTF-8 and embedded
2534NULs through unchanged [perl #97478].
2535
2536=item *
2537
2538C<prototype> now treats magical variables like C<$1> the same way as
2539non-magical variables when checking for the CORE:: prefix, instead of
2540treating them as subroutine names.
2541
2542=item *
2543
2544Under threaded perls, a runtime code block in a regular expression could
2545corrupt the package name stored in the op tree, resulting in bad reads
2546in C<caller>, and possibly crashes [perl #113060].
2547
2548=item *
2549
2550Referencing a closure prototype (C<\&{$_[1]}> in an attribute handler for a
2551closure) no longer results in a copy of the subroutine (or assertion
2552failures on debugging builds).
2553
2554=item *
2555
2556C<eval '__PACKAGE__'> now returns the right answer on threaded builds if
2557the current package has been assigned over (as in
2558C<*ThisPackage:: = *ThatPackage::>) [perl #78742].
2559
2560=item *
2561
2562If a package is deleted by code that it calls, it is possible for C<caller>
2563to see a stack frame belonging to that deleted package. C<caller> could
2564crash if the stash's memory address was reused for a scalar and a
2565substitution was performed on the same scalar [perl #113486].
2566
2567=item *
2568
2569C<UNIVERSAL::can> no longer treats its first argument differently
2570depending on whether it is a string or number internally.
2571
2572=item *
2573
2574C<open> with C<< <& >> for the mode checks to see whether the third argument is
2575a number, in determining whether to treat it as a file descriptor or a handle
2576name. Magical variables like C<$1> were always failing the numeric check and
2577being treated as handle names.
2578
2579=item *
2580
2581C<warn>'s handling of magical variables (C<$1>, ties) has undergone several
2582fixes. C<FETCH> is only called once now on a tied argument or a tied C<$@>
2583[perl #97480]. Tied variables returning objects that stringify as "" are
2584no longer ignored. A tied C<$@> that happened to return a reference the
2585I<previous> time it was used is no longer ignored.
2586
2587=item *
2588
2589C<warn ""> now treats C<$@> with a number in it the same way, regardless of
2590whether it happened via C<$@=3> or C<$@="3">. It used to ignore the
2591former. Now it appends "\t...caught", as it has always done with
2592C<$@="3">.
2593
2594=item *
2595
2596Numeric operators on magical variables (e.g., S<C<$1 + 1>>) used to use
2597floating point operations even where integer operations were more appropriate,
2598resulting in loss of accuracy on 64-bit platforms [perl #109542].
2599
2600=item *
2601
2602Unary negation no longer treats a string as a number if the string happened
2603to be used as a number at some point. So, if C<$x> contains the string "dogs",
2604C<-$x> returns "-dogs" even if C<$y=0+$x> has happened at some point.
2605
2606=item *
2607
e612b5a0 2608In Perl v5.14, C<-'-10'> was fixed to return "10", not "+10". But magical
5ed58cbd
RS
2609variables (C<$1>, ties) were not fixed till now [perl #57706].
2610
2611=item *
2612
2613Unary negation now treats strings consistently, regardless of the internal
2614C<UTF8> flag.
2615
2616=item *
2617
2618A regression introduced in Perl v5.16.0 involving
2619C<tr/I<SEARCHLIST>/I<REPLACEMENTLIST>/> has been fixed. Only the first
2620instance is supposed to be meaningful if a character appears more than
2621once in C<I<SEARCHLIST>>. Under some circumstances, the final instance
2622was overriding all earlier ones. [perl #113584]
2623
2624=item *
2625
2626Regular expressions like C<qr/\87/> previously silently inserted a NUL
2627character, thus matching as if it had been written C<qr/\00087/>. Now it
2628matches as if it had been written as C<qr/87/>, with a message that the
2629sequence C<"\8"> is unrecognized.
2630
2631=item *
2632
2633C<__SUB__> now works in special blocks (C<BEGIN>, C<END>, etc.).
2634
2635=item *
2636
2637Thread creation on Windows could theoretically result in a crash if done
2638inside a C<BEGIN> block. It still does not work properly, but it no longer
2639crashes [perl #111610].
2640
2641=item *
2642
2643C<\&{''}> (with the empty string) now autovivifies a stub like any other
2644sub name, and no longer produces the "Unable to create sub" error
2645[perl #94476].
2646
2647=item *
2648
2649A regression introduced in v5.14.0 has been fixed, in which some calls
2650to the C<re> module would clobber C<$_> [perl #113750].
2651
2652=item *
2653
2654C<do FILE> now always either sets or clears C<$@>, even when the file can't be
2655read. This ensures that testing C<$@> first (as recommended by the
2656documentation) always returns the correct result.
2657
2658=item *
2659
2660The array iterator used for the C<each @array> construct is now correctly
2661reset when C<@array> is cleared (RT #75596). This happens for example when the
2662array is globally assigned to, as in C<@array = (...)>, but not when its
2663B<values> are assigned to. In terms of the XS API, it means that C<av_clear()>
2664will now reset the iterator.
2665
2666This mirrors the behaviour of the hash iterator when the hash is cleared.
2667
2668=item *
2669
2670C<< $class->can >>, C<< $class->isa >>, and C<< $class->DOES >> now return
2671correct results, regardless of whether that package referred to by C<$class>
2672exists [perl #47113].
2673
2674=item *
2675
2676Arriving signals no longer clear C<$@> [perl #45173].
2677
2678=item *
2679
2680Allow C<my ()> declarations with an empty variable list [perl #113554].
2681
2682=item *
2683
2684During parsing, subs declared after errors no longer leave stubs
2685[perl #113712].
2686
2687=item *
2688
2689Closures containing no string evals no longer hang on to their containing
2690subroutines, allowing variables closed over by outer subroutines to be
2691freed when the outer sub is freed, even if the inner sub still exists
2692[perl #89544].
2693
2694=item *
2695
2696Duplication of in-memory filehandles by opening with a "<&=" or ">&=" mode
e612b5a0 2697stopped working properly in v5.16.0. It was causing the new handle to
5ed58cbd
RS
2698reference a different scalar variable. This has been fixed [perl #113764].
2699
2700=item *
2701
2702C<qr//> expressions no longer crash with custom regular expression engines
2703that do not set C<offs> at regular expression compilation time
2704[perl #112962].
2705
2706=item *
2707
2708C<delete local> no longer crashes with certain magical arrays and hashes
2709[perl #112966].
2710
2711=item *
2712
2713C<local> on elements of certain magical arrays and hashes used not to
2714arrange to have the element deleted on scope exit, even if the element did
2715not exist before C<local>.
2716
2717=item *
2718
2719C<scalar(write)> no longer returns multiple items [perl #73690].
2720
2721=item *
2722
2723String to floating point conversions no longer misparse certain strings under
2724C<use locale> [perl #109318].
2725
2726=item *
2727
2728C<@INC> filters that die no longer leak memory [perl #92252].
2729
2730=item *
2731
2732The implementations of overloaded operations are now called in the correct
2733context. This allows, among other things, being able to properly override
2734C<< <> >> [perl #47119].
2735
2736=item *
2737
2738Specifying only the C<fallback> key when calling C<use overload> now behaves
2739properly [perl #113010].
2740
2741=item *
2742
2743C<< sub foo { my $a = 0; while ($a) { ... } } >> and
2744C<< sub foo { while (0) { ... } } >> now return the same thing [perl #73618].
2745
2746=item *
2747
2748String negation now behaves the same under C<use integer;> as it does
2749without [perl #113012].
2750
2751=item *
2752
2753C<chr> now returns the Unicode replacement character (U+FFFD) for -1,
2754regardless of the internal representation. -1 used to wrap if the argument
2755was tied or a string internally.
2756
2757=item *
2758
2759Using a C<format> after its enclosing sub was freed could crash as of
e612b5a0 2760perl v5.12.0, if the format referenced lexical variables from the outer sub.
5ed58cbd
RS
2761
2762=item *
2763
2764Using a C<format> after its enclosing sub was undefined could crash as of
e612b5a0 2765perl v5.10.0, if the format referenced lexical variables from the outer sub.
5ed58cbd
RS
2766
2767=item *
2768
2769Using a C<format> defined inside a closure, which format references
2770lexical variables from outside, never really worked unless the C<write>
e612b5a0 2771call was directly inside the closure. In v5.10.0 it even started crashing.
5ed58cbd
RS
2772Now the copy of that closure nearest the top of the call stack is used to
2773find those variables.
2774
2775=item *
2776
2777Formats that close over variables in special blocks no longer crash if a
2778stub exists with the same name as the special block before the special
2779block is compiled.
2780
2781=item *
2782
2783The parser no longer gets confused, treating C<eval foo ()> as a syntax
2784error if preceded by C<print;> [perl #16249].
2785
2786=item *
2787
2788The return value of C<syscall> is no longer truncated on 64-bit platforms
2789[perl #113980].
2790
2791=item *
2792
2793Constant folding no longer causes C<print 1 ? FOO : BAR> to print to the
2794FOO handle [perl #78064].
2795
2796=item *
2797
2798C<do subname> now calls the named subroutine and uses the file name it
2799returns, instead of opening a file named "subname".
2800
2801=item *
2802
2803Subroutines looked up by rv2cv check hooks (registered by XS modules) are
2804now taken into consideration when determining whether C<foo bar> should be
2805the sub call C<foo(bar)> or the method call C<< "bar"->foo >>.
2806
2807=item *
2808
2809C<CORE::foo::bar> is no longer treated specially, allowing global overrides
2810to be called directly via C<CORE::GLOBAL::uc(...)> [perl #113016].
2811
2812=item *
2813
2814Calling an undefined sub whose typeglob has been undefined now produces the
2815customary "Undefined subroutine called" error, instead of "Not a CODE
2816reference".
2817
2818=item *
2819
2820Two bugs involving @ISA have been fixed. C<*ISA = *glob_without_array> and
2821C<undef *ISA; @{*ISA}> would prevent future modifications to @ISA from
2822updating the internal caches used to look up methods. The
e612b5a0 2823*glob_without_array case was a regression from Perl v5.12.
5ed58cbd
RS
2824
2825=item *
2826
2827Regular expression optimisations sometimes caused C<$> with C</m> to
2828produce failed or incorrect matches [perl #114068].
2829
2830=item *
2831
2832C<__SUB__> now works in a C<sort> block when the enclosing subroutine is
2833predeclared with C<sub foo;> syntax [perl #113710].
2834
2835=item *
2836
2837Unicode properties only apply to Unicode code points, which leads to
2838some subtleties when regular expressions are matched against
2839above-Unicode code points. There is a warning generated to draw your
2840attention to this. However, this warning was being generated
2841inappropriately in some cases, such as when a program was being parsed.
2842Non-Unicode matches such as C<\w> and C<[:word;]> should not generate the
2843warning, as their definitions don't limit them to apply to only Unicode
2844code points. Now the message is only generated when matching against
2845C<\p{}> and C<\P{}>. There remains a bug, [perl #114148], for the very
2846few properties in Unicode that match just a single code point. The
2847warning is not generated if they are matched against an above-Unicode
2848code point.
2849
2850=item *
2851
2852Uninitialized warnings mentioning hash elements would only mention the
2853element name if it was not in the first bucket of the hash, due to an
2854off-by-one error.
2855
2856=item *
2857
2858A regular expression optimizer bug could cause multiline "^" to behave
2859incorrectly in the presence of line breaks, such that
2860C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].
2861
2862=item *
2863
2864Failed C<fork> in list context no longer corrupts the stack.
2865C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
2866if the C<fork> call failed.
2867
2868=item *
2869
2870Numerous memory leaks have been fixed, mostly involving tied variables that
2871die, regular expression character classes and code blocks, and syntax
2872errors.
2873
2874=item *
2875
2876Assigning a regular expression (C<${qr//}>) to a variable that happens to
2877hold a floating point number no longer causes assertion failures on
2878debugging builds.
2879
2880=item *
2881
2882Assigning a regular expression to a scalar containing a number no longer
f105b7be 2883causes subsequent numification to produce random numbers.
5ed58cbd
RS
2884
2885=item *
2886
2887Assigning a regular expression to a magic variable no longer wipes away the
e612b5a0 2888magic. This was a regression from v5.10.
5ed58cbd
RS
2889
2890=item *
2891
2892Assigning a regular expression to a blessed scalar no longer results in
e612b5a0 2893crashes. This was also a regression from v5.10.
5ed58cbd
RS
2894
2895=item *
2896
2897Regular expression can now be assigned to tied hash and array elements with
2898flattening into strings.
2899
2900=item *
2901
f105b7be 2902Numifying a regular expression no longer results in an uninitialized
5ed58cbd
RS
2903warning.
2904
2905=item *
2906
2907Negative array indices no longer cause EXISTS methods of tied variables to
e612b5a0 2908be ignored. This was a regression from v5.12.
5ed58cbd
RS
2909
2910=item *
2911
2912Negative array indices no longer result in crashes on arrays tied to
2913non-objects.
2914
2915=item *
2916
be12dd22
RS
2917C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF-8 if the
2918left-hand scalar happened to have produced a UTF-8 string the last time
5ed58cbd
RS
2919overloading was invoked.
2920
2921=item *
2922
2923C<goto &sub> now uses the current value of @_, instead of using the array
2924the subroutine was originally called with. This means
2925C<local @_ = (...); goto &sub> now works [perl #43077].
2926
2927=item *
2928
2929If a debugger is invoked recursively, it no longer stomps on its own
2930lexical variables. Formerly under recursion all calls would share the same
2931set of lexical variables [perl #115742].
2932
2933=item *
2934
2935C<*_{ARRAY}> returned from a subroutine no longer spontaneously
2936becomes empty.
2937
2938=back
2939
2940=head1 Known Problems
2941
2942=over 4
2943
2944=item *
2945
7f50b25b 2946There are no known regressions. Please report any bugs you find!
5ed58cbd
RS
2947
2948=back
2949
2950=head1 Acknowledgements
a75569c0 2951
5ed58cbd 2952XXX Generate this with:
a75569c0 2953
5ed58cbd 2954 perl Porting/acknowledgements.pl v5.18.0..HEAD
f5b73711 2955
44691e6f
AB
2956=head1 Reporting Bugs
2957
e08634c5
SH
2958If you find what you think is a bug, you might check the articles recently
2959posted to the comp.lang.perl.misc newsgroup and the perl bug database at
2960http://rt.perl.org/perlbug/ . There may also be information at
2961http://www.perl.org/ , the Perl Home Page.
44691e6f 2962
e08634c5
SH
2963If you believe you have an unreported bug, please run the L<perlbug> program
2964included with your release. Be sure to trim your bug down to a tiny but
2965sufficient test case. Your bug report, along with the output of C<perl -V>,
2966will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
44691e6f
AB
2967
2968If the bug you are reporting has security implications, which make it
e08634c5
SH
2969inappropriate to send to a publicly archived mailing list, then please send it
2970to perl5-security-report@perl.org. This points to a closed subscription
2971unarchived mailing list, which includes all the core committers, who will be
2972able to help assess the impact of issues, figure out a resolution, and help
f9001595 2973co-ordinate the release of patches to mitigate or fix the problem across all
e08634c5
SH
2974platforms on which Perl is supported. Please only use this address for
2975security issues in the Perl core, not for modules independently distributed on
2976CPAN.
44691e6f
AB
2977
2978=head1 SEE ALSO
2979
e08634c5
SH
2980The F<Changes> file for an explanation of how to view exhaustive details on
2981what changed.
44691e6f
AB
2982
2983The F<INSTALL> file for how to build Perl.
2984
2985The F<README> file for general stuff.
2986
2987The F<Artistic> and F<Copying> files for copyright information.
2988
2989=cut