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1=encoding utf8
2
3=head1 NAME
4
0bba4573 5perl5180delta - what is new for perl v5.18.0
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6
7=head1 DESCRIPTION
8
0bba4573 9This document describes differences between the 5.16.0 release and the 5.18.0
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10release.
11
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12If you are upgrading from an earlier release such as 5.16.0, first read
13L<perl5160delta>, which describes differences between 5.14.0 and 5.16.0.
e5ba1bf1 14
5946c067 15=head1 Core Enhancements
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17=head2 New mechanism for experimental features
18
19Newly-added experimental features will now require this incantation:
20
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
5946c067 44=head2 Hash overhaul
e5ba1bf1 45
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46Changes to the implementation of hashes in perl 5.18.0 will be one of the most
47visible changes to the behavior of existing code. For the most part, these
48changes will be visible as two distinct hash variables now providing their
0309f1e2 49contents in a different order where it was previously identical. When
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50encountering these changes, the key to cleaning up from them is to accept that
51B<hashes are unordered collections> and to act accordingly.
52
53=head3 Hash randomization
54
55The seed used by Perl's hash function is now random. This means that the
56order which keys/values will be returned from functions like C<keys()>,
57C<values()>, and C<each()> will differ from run to run.
58
59This change was introduced to make Perl's hashes more robust to algorithmic
60complexity attacks, and also because we discovered that it exposes hash
61ordering dependency bugs and makes them easier to track down.
62
63Toolchain maintainers might want to invest in additional infrastructure to
64test for things like this. Running tests several times in a row and then
65comparing results will make it easier to spot hash order dependencies in
66code. Authors are strongly encouraged not to expose the key order of
67Perl's hashes to insecure audiences.
68
69Further, every hash has its own iteration order, which should make it much
70more difficult to determine what the current hash seed is.
71
72=head3 New hash function: Murmurhash-32
73
74We have switched Perl's hash function to use Murmurhash-32, and added build
75support for several other hash functions. This new function is expected to
76perform equivalently to the old one for shorter strings and is faster for
77hashing longer strings.
78
79=head3 PERL_HASH_SEED enviornment variable now takes a hex value
80
81PERL_HASH_SEED no longer accepts an integer as a parameter, instead the
82value is expected to be a binary string encoded in hex. This is to make
83the infrastructure support hash seeds of arbitrary lengths which might
84exceed that of an integer. (SipHash uses a 16 byte seed).
85
86=head3 Hash::Util::hash_seed() now returns a string
87
88Hash::Util::hash_seed() now returns a string instead of an integer. This
89is to make the infrastructure support hash seeds of arbitrary lengths
90which might exceed that of an integer. (SipHash uses a 16 byte seed).
91
92=head3 Output of PERL_HASH_SEED_DEBUG has been changed
93
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94The environment variable PERL_HASH_SEED_DEBUG now makes perl show both the
95hash function perl was built with AND the seed, in hex, in use for that
96process. Code parsing this output, should it exist, must change to accomodate
97the new format. Example of the new format:
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98
99 $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
100 HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f
e5ba1bf1 101
d29861e7 102=head2 Upgrade to Unicode 6.2
816361ee 103
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104Perl now supports the final version of Unicode 6.2. Earlier releases in
105the 5.17 series supported Unicode 6.2 beta versions. There were no
106substantive changes in the final Unicode 6.2 version from the most
107recent beta, included in Perl 5.17.4. A list of changes from Unicode
1086.1 is at L<http://www.unicode.org/versions/Unicode6.2.0>.
816361ee 109
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110=head2 Character name aliases may now include non-Latin1-range characters
111
112It is possible to define your own names for characters for use in
113C<\N{...}>, C<charnames::vianame()>, etc. These names can now be
114comprised of characters from the whole Unicode range. This allows for
115names to be in your native language, and not just English. Certain
116restrictions apply to the characters that may be used (you can't define
117a name that has punctuation in it, for example). See L<charnames/CUSTOM
118ALIASES>.
119
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120=head2 New DTrace probes
121
122The following new DTrace probes have been added:
123
124=over 4
125
126=item C<op-entry>
127
128=item C<loading-file>
129
130=item C<loaded-file>
131
132=back
133
134=head2 C<${^LAST_FH}>
135
136This new variable provides access to the filehandle that was last read.
137This is the handle used by C<$.> and by C<tell> and C<eof> without
138arguments.
139
d29861e7 140=head2 Regular Expression Set Operations
00785cb7 141
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142This is an B<experimental> feature to allow matching against the union,
143intersection, etc., of sets of code points, similar to
144L<Unicode::Regex::Set>. It can also be used to extend C</x> processing
145to [bracketed] character classes, and as a replacement of user-defined
146properties, allowing more complex expressions than they do. See
147L<perlre/(?[ ])>.
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148
149=head2 Lexical subroutines
150
d29861e7 151This new feature is still considered B<experimental>. To enable it:
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152
153 use 5.018;
7a3f436e 154 no warnings "experimental::lexical_subs";
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155 use feature "lexical_subs";
156
157You can now declare subroutines with C<state sub foo>, C<my sub foo>, and
158C<our sub foo>. (C<state sub> requires that the "state" feature be
159enabled, unless you write it as C<CORE::state sub foo>.)
160
161C<state sub> creates a subroutine visible within the lexical scope in which
162it is declared. The subroutine is shared between calls to the outer sub.
163
164C<my sub> declares a lexical subroutine that is created each time the
165enclosing block is entered. C<state sub> is generally slightly faster than
166C<my sub>.
167
168C<our sub> declares a lexical alias to the package subroutine of the same
169name.
170
d29861e7 171For more information, see L<perlsub/Lexical Subroutines>.
00785cb7 172
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173=head2 Computed Labels
174
175The loop controls C<next>, C<last> and C<redo>, and the special C<dump>
176operator, now allow arbitrary expressions to be used to compute labels at run
177time. Previously, any argument that was not a constant was treated as the
178empty string.
179
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180=head2 More CORE:: subs
181
182Several more built-in functions have been added as subroutines to the
183CORE:: namespace, namely, those non-overridable keywords that can be
184implemented without custom parsers: C<defined>, C<delete>, C<exists>,
185C<glob>, C<pos>, C<protoytpe>, C<scalar>, C<split>, C<study>, and C<undef>.
186
187As some of these have prototypes, C<prototype('CORE::...')> has been
188changed to not make a distinction between overridable and non-overridable
189keywords. This is to make C<prototype('CORE::pos')> consistent with
190C<prototype(&CORE::pos)>.
e5ba1bf1 191
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192=head2 C<kill> with negative signal names
193
194C<kill> has always allowed a negative signal number, which kills the
195process group instead of a single process. It has also allowed signal
196names. But it did not behave consistently, because negative signal names
197were treated as 0. Now negative signals names like C<-INT> are supported
198and treated the same way as -2 [perl #112990].
199
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200=head1 Security
201
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202=head2 C<Storable> security warning in documentation
203
204The documentation for C<Storable> now includes a section which warns readers
205of the danger of accepting Storable documents from untrusted sources. The
206short version is that deserializing certain types of data can lead to loading
207modules and other code execution. This is documented behavior and wanted
208behavior, but this opens an attack vector for malicious entities.
209
210=head2 C<Locale::Maketext> allowed code injection via a malicious template
211
212If users could provide a translation string to Locale::Maketext, this could be
213used to invoke arbitrary Perl subroutines available in the current process.
214
215This has been fixed, but it is still possible to invoke any method provided by
216C<Locale::Maketext> itself or a subclass that you are using. One of these
217methods in turn will invoke the Perl core's C<sprintf> subroutine.
218
219In summary, allowing users to provide translation strings without auditing
220them is a bad idea.
221
222This vulnerability is documented in CVE-2012-6329.
223
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224=head2 Avoid calling memset with a negative count
225
226Poorly written perl code that allows an attacker to specify the count to perl's
227C<x> string repeat operator can already cause a memory exhaustion
228denial-of-service attack. A flaw in versions of perl before 5.15.5 can escalate
229that into a heap buffer overrun; coupled with versions of glibc before 2.16, it
230possibly allows the execution of arbitrary code.
231
232The flaw addressed to this commit has been assigned identifier CVE-2012-5195
233and was researched by Tim Brown.
234
235=head1 Incompatible Changes
236
237=head2 See also: hash overhaul
238
239Some of the changes in the L<hash overhaul|/"Hash overhaul"> are not fully
240compatible with previous versions of perl. Please read that section.
241
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242=head2 An unknown character name in C<\N{...}> is now a syntax error
243
244Previously, it warned, and the Unicode REPLACEMENT CHARACTER was
245substituted. Unicode now recommends that this situation be a syntax
246error. Also, the previous behavior led to some confusing warnings and
247behaviors, and since the REPLACEMENT CHARACTER has no use other than as
248a stand-in for some unknown character, any code that has this problem is
249buggy.
250
251=head2 Formerly deprecated characters in C<\N{}> character name aliases are now errors.
252
253Since v5.12.0, it has been deprecated to use certain characters in
254user-defined C<\N{...}> character names. These now cause a syntax
255error. For example, it is now an error to begin a name with a digit,
256such as in
257
258 my $undraftable = "\N{4F}"; # Syntax error!
259
260or to have commas anywhere in the name. See L<charnames/CUSTOM ALIASES>
261
2516b9f0 262=head2 C<\N{BELL}> now refers to U+1F514 instead of U+0007
e5ba1bf1 263
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264Unicode 6.0 reused the name "BELL" for a different code point than it
265traditionally had meant. Since Perl v5.14, use of this name still
266referred to U+0007, but would raise a deprecation warning. Now, "BELL"
267refers to U+1F514, and the name for U+0007 is "ALERT". All the
268functions in L<charnames> have been correspondingly updated.
e5ba1bf1 269
2516b9f0 270=head2 New Restrictions in Multi-Character Case-Insensitive Matching in Regular Expression Bracketed Character Classes
5946c067 271
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272Unicode has now withdrawn their previous recommendation for regular
273expressions to automatically handle cases where a single character can
274match multiple characters case-insensitively; for example, the letter
275LATIN SMALL LETTER SHARP S and the sequence C<ss>. This is because
276it turns out to be impracticable to do this correctly in all
277circumstances. Because Perl has tried to do this as best it can, it
278will continue to do so. (We are considering an option to turn it off.)
279However, a new restriction is being added on such matches when they
280occur in [bracketed] character classes. People were specifying
281things such as C</[\0-\xff]/i>, and being surprised that it matches the
282two character sequence C<ss> (since LATIN SMALL LETTER SHARP S occurs in
283this range). This behavior is also inconsistent with the using a
284property instead of a range: C<\p{Block=Latin1}> also includes LATIN
285SMALL LETTER SHARP S, but C</[\p{Block=Latin1}]/i> does not match C<ss>.
286The new rule is that for there to be a multi-character case-insensitive
287match within a bracketed character class, the character must be
288explicitly listed, and not as an end point of a range. This more
289closely obeys the Principle of Least Astonishment. See
290L<perlrecharclass/Bracketed Character Classes>. Note that a bug [perl
291#89774], now fixed as part of this change, prevented the previous
292behavior from working fully.
5946c067 293
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294=head2 Explicit rules for variable names and identifiers
295
296Due to an oversight, length-one variable names in 5.16 were completely
297unrestricted, and opened the door to several kinds of insanity. As of
2985.18, these now follow the rules of other identifiers, in addition
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299to accepting characters that match the C<\p{POSIX_Punct}> property.
300
301There are no longer any differences in the parsing of identifiers
302specified as C<$...> or C<${...};> previously, they were dealt with in
303different parts of the core, and so had slightly different behavior. For
304instance, C<${foo:bar}> was a legal variable name. Since they are now
305both parsed by the same code, that is no longer the case.
306
307=head2 C<\s> in regular expressions now matches a Vertical Tab
308
309No one could recall why C<\s> didn't match C<\cK>, the vertical tab.
310Now it does. Given the extreme rarity of that character, very little
311breakage is expected.
312
313=head2 C</(?{})/> and C</(??{})/> have been heavily reworked
314
315The implementation of this feature has been almost completely rewritten.
316Although its main intent is to fix bugs, some behaviors, especially
317related to the scope of lexical variables, will have changed. This is
318described more fully in the L</Selected Bug Fixes> section.
319
320=head2 Stricter parsing of substitution replacement
0d146223 321
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322It is no longer possible to abuse the way the parser parses C<s///e> like
323this:
324
325 %_=(_,"Just another ");
326 $_="Perl hacker,\n";
327 s//_}->{_/e;print
328
329=head2 C<given> now aliases the global C<$_>
330
331Instead of assigning to an implicit lexical C<$_>, C<given> now makes the
332global C<$_> an alias for its argument, just like C<foreach>. However, it
333still uses lexical C<$_> if there is lexical C<$_> in scope (again, just like
334C<foreach>) [perl #114020].
0d146223 335
2516b9f0 336=head2 Lexical $_ is now experimental
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337
338Since it was introduced in Perl 5.10, it has caused much confusion with no
339obvious solution:
340
341=over
342
343=item *
344
345Various modules (e.g., List::Util) expect callback routines to use the
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346global C<$_>. C<use List::Util 'first'; my $_; first { $_ == 1 } @list>
347does not work as one would expect.
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348
349=item *
350
351A C<my $_> declaration earlier in the same file can cause confusing closure
352warnings.
353
354=item *
355
356The "_" subroutine prototype character allows called subroutines to access
2516b9f0 357your lexical C<$_>, so it is not really private after all.
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358
359=item *
360
361Nevertheless, subroutines with a "(@)" prototype and methods cannot access
2516b9f0 362the caller's lexical C<$_>, unless they are written in XS.
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363
364=item *
365
2516b9f0 366But even XS routines cannot access a lexical C<$_> declared, not in the
d268df4d 367calling subroutine, but in an outer scope, iff that subroutine happened not
2516b9f0 368to mention C<$_> or use any operators that default to C<$_>.
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369
370=back
371
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372It is our hope that lexical C<$_> can be rehabilitated, but this may
373cause changes in its behavior. Please use it with caution until it
374becomes stable.
375
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376=head2 readline() with C<$/ = \N> now reads N characters, not N bytes
377
378Previously, when reading from a stream with I/O layers such as
379C<encoding>, the readline() function, otherwise known as the C<< <> >>
380operator, would read I<N> bytes from the top-most layer. [perl #79960]
381
382Now, I<N> characters are read instead.
383
384There is no change in behaviour when reading from streams with no
385extra layers, since bytes map exactly to characters.
386
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387=head2 Overridden C<glob> is now passed one argument
388
389C<glob> overrides used to be passed a magical undocumented second argument
390that identified the caller. Nothing on CPAN was using this, and it got in
391the way of a bug fix, so it was removed. If you really need to identify
392the caller, see L<Devel::Callsite> on CPAN.
393
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394=head2 Here-doc parsing
395
396The body of a here-document inside a quote-like operator now always begins
397on the line after the "<<foo" marker. Previously, it was documented to
398begin on the line following the containing quote-like operator, but that
399was only sometimes the case [perl #114040].
400
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401=head2 Alphanumeric operators must now be separated from the closing
402delimiter of regular expressions
00785cb7 403
2516b9f0 404You may no longer write something like:
00785cb7 405
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406 m/a/and 1
407
408Instead you must write
409
410 m/a/ and 1
411
412with whitespace separating the operator from the closing delimiter of
413the regular expression. Not having whitespace has resulted in a
414deprecation warning since Perl v5.14.0.
415
416=head2 qw(...) can no longer be used as parentheses
417
418C<qw> lists used to fool the parser into thinking they were always
419surrounded by parentheses. This permitted some surprising constructions
420such as C<foreach $x qw(a b c) {...}>, which should really be written
421C<foreach $x (qw(a b c)) {...}>. These would sometimes get the lexer into
422the wrong state, so they didn't fully work, and the similar C<foreach qw(a
423b c) {...}> that one might expect to be permitted never worked at all.
424
425This side effect of C<qw> has now been abolished. It has been deprecated
426since Perl 5.13.11. It is now necessary to use real parentheses
427everywhere that the grammar calls for them.
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428
429=head2 Interaction of lexical and default warnings
430
431Turning on any lexical warnings used first to disable all default warnings
432if lexical warnings were not already enabled:
433
434 $*; # deprecation warning
435 use warnings "void";
436 $#; # void warning; no deprecation warning
437
438Now, the debugging, deprecated, glob, inplace and malloc warnings
439categories are left on when turning on lexical warnings (unless they are
440turned off by C<no warnings>, of course).
441
442This may cause deprecation warnings to occur in code that used to be free
443of warnings.
444
445Those are the only categories consisting only of default warnings. Default
446warnings in other categories are still disabled by C<use warnings
447"category">, as we do not yet have the infrastructure for controlling
448individual warnings.
449
450=head2 C<state sub> and C<our sub>
451
452Due to an accident of history, C<state sub> and C<our sub> were equivalent
453to a plain C<sub>, so one could even create an anonymous sub with
454C<our sub { ... }>. These are now disallowed outside of the "lexical_subs"
455feature. Under the "lexical_subs" feature they have new meanings described
456in L<perlsub/Lexical Subroutines>.
457
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458=head2 Defined values stored in environment are forced to byte strings
459
460A value stored in an environment variable has always been stringified. In this
461release, it is converted to be only a byte string. First, it is forced to be a
462only a string. Then if the string is utf8 and the equivalent of
463C<utf8::downgrade()> works, that result is used; otherwise, the equivalent of
464C<utf8::encode()> is used, and a warning is issued about wide characters
465(L</Diagnostics>).
466
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467=head2 C<require> dies for unreadable files
468
469When C<require> encounters an unreadable file, it now dies. It used to
2516b9f0 470ignore the file and continue searching the directories in C<@INC>
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471[perl #113422].
472
2516b9f0 473=head2 C<gv_fetchmeth_*> and SUPER
0fef449b 474
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475The various C<gv_fetchmeth_*> XS functions used to treat a package whose
476named ended with ::SUPER specially. A method lookup on the Foo::SUPER
477package would be treated as a SUPER method lookup on the Foo package. This
478is no longer the case. To do a SUPER lookup, pass the Foo stash and the
479GV_SUPER flag.
0fef449b 480
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481=head1 Deprecations
482
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483=head2 Deprecated modules
484
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485The following modules will be removed from the core distribution in a
486future release, and should be installed from CPAN instead. Distributions
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487on CPAN which require these should add them to their prerequisites.
488The core versions of these modules will issue "deprecated"-category
489warnings.
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490
491You can silence these deprecation warnings by installing the modules
492in question from CPAN.
493
494=over
495
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496=item L<Archive::Extract>
497
498=item L<B::Lint>
499
500=item L<B::Lint::Debug>
501
1ebc7ce8 502=item L<CPANPLUS> and all included C<CPANPLUS::*> modules
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503
504=item L<Devel::InnerPackage>
505
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506=item L<encoding>
507
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508=item L<Log::Message>
509
510=item L<Log::Message::Config>
511
512=item L<Log::Message::Handlers>
513
514=item L<Log::Message::Item>
515
516=item L<Log::Message::Simple>
517
518=item L<Module::Pluggable>
519
520=item L<Module::Pluggable::Object>
521
522=item L<Object::Accessor>
523
524=item L<Pod::LaTeX>
525
526=item L<Term::UI>
527
528=item L<Term::UI::History>
529
530=back
531
532=head2 Deprecated Utilities
533
534The following utilities will be removed from the core distribution in a
535future release as their associated modules have been deprecated. They
536will remain available with the applicable CPAN distribution.
537
538=over
539
540=item L<cpanp>
541
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542=item C<cpanp-run-perl>
543
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544=item L<cpan2dist>
545
1ebc7ce8 546These items are part of the C<CPANPLUS> distribution.
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547
548=item L<pod2latex>
549
1ebc7ce8 550This item is part of the C<Pod::LaTeX> distribution.
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551
552=back
553
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554=head2 PL_sv_objcount
555
556This interpreter-global variable used to track the total number of
557Perl objects in the interpreter. It is no longer maintained and will
558be removed altogether in Perl 5.20.
559
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560=head2 Five additional characters should be escaped in patterns with C</x>
561
562When a regular expression pattern is compiled with C</x>, Perl treats 6
563characters as white space to ignore, such as SPACE and TAB. However,
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564Unicode recommends 11 characters be treated thusly. We will conform
565with this in a future Perl version. In the meantime, use of any of the
566missing characters will raise a deprecation warning, unless turned off.
567The five characters are:
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568U+0085 NEXT LINE,
569U+200E LEFT-TO-RIGHT MARK,
570U+200F RIGHT-TO-LEFT MARK,
571U+2028 LINE SEPARATOR,
572and
573U+2029 PARAGRAPH SEPARATOR.
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574
575=head2 User-defined charnames with surprising whitespace
576
577A user-defined character name with trailing or multiple spaces in a row is
578likely a typo. This now generates a warning when defined, on the assumption
579that uses of it will be unlikely to include the excess whitespace.
580
581=head2 Various XS-callable functions are now deprecated
582
583All the functions used to classify characters will be removed from a
584future version of Perl, and should not be used. With participating C
585compilers (e.g., gcc), compiling any file that uses any of these will
586generate a warning. These were not intended for public use; there are
587equivalent, faster, macros for most of them.
588See L<perlapi/Character classes>. The complete list (including some
589that were deprecated in 5.17.7) is:
590C<is_uni_alnum>, C<is_uni_alnumc>, C<is_uni_alnumc_lc>,
591C<is_uni_alnum_lc>, C<is_uni_alpha>, C<is_uni_alpha_lc>,
592C<is_uni_ascii>, C<is_uni_ascii_lc>, C<is_uni_blank>,
593C<is_uni_blank_lc>, C<is_uni_cntrl>, C<is_uni_cntrl_lc>,
594C<is_uni_digit>, C<is_uni_digit_lc>, C<is_uni_graph>,
595C<is_uni_graph_lc>, C<is_uni_idfirst>, C<is_uni_idfirst_lc>,
596C<is_uni_lower>, C<is_uni_lower_lc>, C<is_uni_print>,
597C<is_uni_print_lc>, C<is_uni_punct>, C<is_uni_punct_lc>,
598C<is_uni_space>, C<is_uni_space_lc>, C<is_uni_upper>,
599C<is_uni_upper_lc>, C<is_uni_xdigit>, C<is_uni_xdigit_lc>,
600C<is_utf8_alnum>, C<is_utf8_alnumc>, C<is_utf8_alpha>,
601C<is_utf8_ascii>, C<is_utf8_blank>, C<is_utf8_char>,
602C<is_utf8_cntrl>, C<is_utf8_digit>, C<is_utf8_graph>,
603C<is_utf8_idcont>, C<is_utf8_idfirst>, C<is_utf8_lower>,
604C<is_utf8_mark>, C<is_utf8_perl_space>, C<is_utf8_perl_word>,
605C<is_utf8_posix_digit>, C<is_utf8_print>, C<is_utf8_punct>,
606C<is_utf8_space>, C<is_utf8_upper>, C<is_utf8_xdigit>,
607C<is_utf8_xidcont>, C<is_utf8_xidfirst>.
608
609In addition these three functions that have never worked properly are
610deprecated:
611C<to_uni_lower_lc>, C<to_uni_title_lc>, and C<to_uni_upper_lc>.
612
613=head2 Certain rare uses of backslashes within regexes are now deprectated
614
615There are three pairs of characters that Perl recognizes as
616metacharacters in regular expression patterns: C<{}>, C<[]>, and C<()>.
617These can be used as well to delimit patterns, as in:
618
1ebc7ce8
RS
619 m{foo}
620 s(foo)(bar)
816361ee
RS
621
622Since they are metacharacters, they have special meaning to regular
623expression patterns, and it turns out that you can't turn off that
624special meaning by the normal means of preceding them with a backslash,
625if you use them, paired, within a pattern delimitted by them. For
626example, in
627
1ebc7ce8 628 m{foo\{1,3\}}
816361ee
RS
629
630the backslashes do not change the behavior, and this matches
631S<C<"f o">> followed by one to three more occurrences of C<"o">.
632
633Usages like this, where they are interpreted as metacharacters, are
634exceedingly rare; we think there are none, for example, in all of CPAN.
635Hence, this deprecation should affect very little code. It does give
636notice, however, that any such code needs to change, which will in turn
637allow us to change the behavior in future Perl versions so that the
638backslashes do have an effect, and without fear that we are silently
639breaking any existing code.
640
bea832c0
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641=head1 Future Deprecations
642
643=over
644
645=item *
646
647Platforms with out support infrastructure
648
649Both Windows CE and z/OS have been historically under-maintained, and are
650currently neither successfully building nor regularly being smoke tested.
651Efforts are underway to change this situation, but it should not be taken for
71b6ff97
RS
652granted that the platforms are safe and supported. If they do not become
653buildable and regularly smoked, support for them may be actively removed in
654future releases. If you have an interest in these platforms and you can lend
655your time, expertise, or hardware to help support these platforms, please let
656the perl development effort know by emailing C<perl5-porters@perl.org>.
657
658Some platforms that appear otherwise entirely dead are also on the short list
659for removal between now and 5.20.0:
660
661=over
662
663=item DG/UX
664
665=item NeXT
666
667=back
bea832c0
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668
669=item *
670
671Swapping of $< and $>
672
673For more information about this future deprecation, see L<the relevant RT
674ticket|https://rt.perl.org/rt3/Ticket/Display.html?id=96212>.
675
676=item *
677
678sfio, stdio
679
680Perl supports being built without PerlIO proper, using a stdio or sfio
681wrapper instead. A perl build like this will not support IO layers and
682thus Unicode IO, making it rather handicapped.
683
684PerlIO supports a C<stdio> layer if stdio use is desired, and similarly a
685sfio layer could be produced.
686
687=item *
688
71b6ff97
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689C<microperl>, long broken and of unclear present purpose, will be removed.
690
691=item *
692
bea832c0
RS
693Revamping C<< "\Q" >> semantics in double-quotish strings when combined with
694other escapes.
695
696There are several bugs and inconsistencies involving combinations
697of C<\Q> and escapes like C<\x>, C<\L>, etc., within a C<\Q...\E> pair.
698These need to be fixed, and doing so will necessarily change current
699behavior. The changes have not yet been settled.
700
701=back
702
e5ba1bf1
FC
703=head1 Performance Enhancements
704
7e7c78a1
RS
705=over 4
706
707=item *
e5ba1bf1 708
7e7c78a1 709Lists of lexical variable declarations (C<my($x, $y)>) are now optimised
9abd6633 710down to a single op and are hence faster than before.
e5ba1bf1 711
7e7c78a1
RS
712=item *
713
9abd6633
RS
714A new C preprocessor define C<NO_TAINT_SUPPORT> was added that, if set,
715disables Perl's taint support altogether. Using the -T or -t command
716line flags will cause a fatal error. Beware that both core tests as
717well as many a CPAN distribution's tests will fail with this change. On
718the upside, it provides a small performance benefit due to reduced
719branching.
7e7c78a1
RS
720
721B<Do not enable this unless you know exactly what you are getting yourself
722into.>
e5ba1bf1
FC
723
724=item *
725
d29861e7
RS
726C<pack> with constant arguments is now constant folded in most cases
727[perl #113470].
728
729=item *
730
00785cb7 731Speed up in regular expression matching against Unicode properties. The
9abd6633 732largest gain is for C<\X>, the Unicode "extended grapheme cluster." The
00785cb7
RS
733gain for it is about 35% - 40%. Bracketed character classes, e.g.,
734C<[0-9\x{100}]> containing code points above 255 are also now faster.
735
736=item *
737
738On platforms supporting it, several former macros are now implemented as static
739inline functions. This should speed things up slightly on non-GCC platforms.
740
741=item *
742
9abd6633
RS
743Apply the optimisation of hashes in boolean context, such as in C<if> or
744C<and>, to constructs in non-void context.
00785cb7
RS
745
746=item *
747
748Extend the optimisation of hashes in boolean context to C<scalar(%hash)>,
749C<%hash ? ... : ...>, and C<sub { %hash || ... }>.
750
751=item *
752
0bba4573
RS
753Filetest ops manage the stack in a fractionally more efficient manner.
754
755=item *
756
9abd6633 757Globs used in a numeric context are now numified directly in most cases,
0bba4573 758rather than being numerified via stringification.
e5ba1bf1 759
0fef449b
RS
760=item *
761
762The C<x> repetition operator is now folded to a single constant at compile
763time if called in scalar context with constant operands and no parentheses
764around the left operand.
765
e5ba1bf1
FC
766=back
767
768=head1 Modules and Pragmata
769
e5ba1bf1
FC
770=head2 New Modules and Pragmata
771
772=over 4
773
774=item *
775
e7ae12cf
RS
776L<Config::Perl::V> version 0.16 has been added as a dual-lifed module.
777It provides structured data retrieval of C<perl -V> output including
778information only known to the C<perl> binary and not available via L<Config>.
e5ba1bf1
FC
779
780=back
781
782=head2 Updated Modules and Pragmata
783
9abd6633
RS
784This is only an overview of selected module updates. For a complete
785list of updates, run:
786
787 $ corelist --diff 5.14.0 5.16.0
788
789You can substitute your favorite version in place of 5.14.0, too.
790
e5ba1bf1
FC
791=over 4
792
793=item *
794
795L<XXX> has been upgraded from version A.xx to B.yy.
796
797=back
798
799=head2 Removed Modules and Pragmata
800
0bba4573 801=over
e5ba1bf1
FC
802
803=item *
804
0bba4573
RS
805L<Version::Requirements> has been removed from the core distribution. It is
806available under a different name: L<CPAN::Meta::Requirements>.
e5ba1bf1
FC
807
808=back
809
810=head1 Documentation
811
9abd6633 812=head2 Changes to Existing Documentation
e5ba1bf1 813
9abd6633 814=head3 L<perlcheat>
e5ba1bf1 815
9abd6633 816=over 4
e5ba1bf1 817
9abd6633 818=item *
e5ba1bf1 819
9abd6633 820L<perlcheat> has been reorganized, and a few new sections were added.
e5ba1bf1 821
9abd6633 822=back
e5ba1bf1 823
0bba4573 824=head3 L<perldata>
e5ba1bf1 825
0bba4573
RS
826=over 4
827
828=item *
829
830Now explicitly documents the behaviour of hash initializer lists that
831contain duplicate keys.
832
833=back
834
835=head3 L<perldiag>
836
837=over 4
838
839=item *
840
841The explanation of symbolic references being prevented by "strict refs"
842now doesn't assume that the reader knows what symbolic references are.
843
844=back
845
9abd6633 846=head3 L<perlfaq>
e5ba1bf1
FC
847
848=over 4
849
850=item *
851
9abd6633 852L<perlfaq> has been synchronized with version 5.0150040 from CPAN.
37133b20 853
e5ba1bf1
FC
854=back
855
9abd6633 856=head3 L<perlfunc>
0fef449b
RS
857
858=over 4
859
860=item *
861
9abd6633 862The return value of C<pipe> is now documented.
0fef449b
RS
863
864=item *
865
9abd6633 866Clarified documentation of C<our>.
0fef449b
RS
867
868=back
869
94b31d3f
RS
870=head3 L<perlop>
871
872=over 4
873
874=item *
875
876Loop control verbs (C<dump>, C<goto>, C<next>, C<last> and C<redo>) have always
877had the same precedence as assignment operators, but this was not documented
878until now.
879
880=back
881
0bba4573 882=head3 Diagnostics
e5ba1bf1
FC
883
884The following additions or changes have been made to diagnostic output,
885including warnings and fatal error messages. For the complete list of
886diagnostic messages, see L<perldiag>.
887
888XXX New or changed warnings emitted by the core's C<C> code go here. Also
889include any changes in L<perldiag> that reconcile it to the C<C> code.
890
891=head2 New Diagnostics
892
893XXX Newly added diagnostic messages go under here, separated into New Errors
894and New Warnings
895
896=head3 New Errors
897
898=over 4
899
900=item *
901
94b31d3f
RS
902L<Unterminated delimiter for here document|perldiag/"Unterminated delimiter for here document">
903
904This message now occurs when a here document label has an initial quotation
905mark but the final quotation mark is missing.
906
907This replaces a bogus and misleading error message about not finding the label
908itself [perl #114104].
909
910=item *
911
912L<panic: child pseudo-process was never scheduled|perldiag/"panic: child pseudo-process was never scheduled">
913
914This error is thrown when a child pseudo-process in the ithreads implementation
915on Windows was not scheduled within the time period allowed and therefore was
916not able to initialize properly [perl #88840].
917
918=item *
919
37133b20
RS
920L<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/">
921
922This error has been added for C<(?&0)>, which is invalid. It used to
923produce an incomprehensible error message [perl #101666].
924
925=item *
926
927L<Can't use an undefined value as a subroutine reference|perldiag/"Can't use an undefined value as %s reference">
928
929Calling an undefined value as a subroutine now produces this error message.
930It used to, but was accidentally disabled, first in Perl 5.004 for
931non-magical variables, and then in Perl 5.14 for magical (e.g., tied)
932variables. It has now been restored. In the mean time, undef was treated
933as an empty string [perl #113576].
e5ba1bf1
FC
934
935=back
936
937=head3 New Warnings
938
939=over 4
940
941=item *
942
0d146223
RS
943L<%c* is deprecated, and will become a syntax error|perldiag/"%c* is deprecated, and will become a syntax error">
944
945Use of C<@*>, C<&*>, C<**> or C<%*> is now deprecated, and will generate a
946compile time warning, enabled by default. In future such code will fail to
947compile with a syntax error. Removing these variables, along with C<$*>,
948will permit future syntax additions.
949
950=item *
951
e7ae12cf
RS
952XXX: This needs more detail.
953
954Strings with code points over 0xFF may not be mapped into in-memory file
955handles
956
957=item *
958
816361ee
RS
959L<'%s' resolved to '\o{%s}%d'|perldiag/"'%s' resolved to '\o{%s}%d'">
960
961=item *
962
963L<'Trailing white-space in a charnames alias definition is deprecated'|perldiag/"Trailing white-space in a charnames alias definition is deprecated">
964
965=item *
966
967L<'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">
968
969=item *
970
971L<'Passing malformed UTF-8 to "%s" is deprecated'|perldiag/"Passing malformed UTF-8 to "%s" is deprecated">
972
816361ee
RS
973=item *
974
00785cb7
RS
975L<Experimental "%s" subs not enabled|perldiag/"Experimental "%s" subs not enabled">
976
977(F) To use lexical subs, you must first enable them:
978
7a3f436e 979 no warnings 'experimental::lexical_subs';
00785cb7
RS
980 use feature 'lexical_subs';
981 my sub foo { ... }
982
983=item *
984
985L<Subroutine "&%s" is not available|perldiag/"Subroutine "&%s" is not available">
986
987(W closure) During compilation, an inner named subroutine or eval is
988attempting to capture an outer lexical subroutine that is not currently
989available. This can happen for one of two reasons. First, the lexical
990subroutine may be declared in an outer anonymous subroutine that has not
991yet been created. (Remember that named subs are created at compile time,
992while anonymous subs are created at run-time.) For example,
993
994 sub { my sub a {...} sub f { \&a } }
995
996At the time that f is created, it can't capture the current the "a" sub,
997since the anonymous subroutine hasn't been created yet. Conversely, the
998following won't give a warning since the anonymous subroutine has by now
999been created and is live:
1000
1001 sub { my sub a {...} eval 'sub f { \&a }' }->();
1002
1003The second situation is caused by an eval accessing a variable that has
1004gone out of scope, for example,
1005
1006 sub f {
9abd6633
RS
1007 my sub a {...}
1008 sub { eval '\&a' }
00785cb7
RS
1009 }
1010 f()->();
1011
1012Here, when the '\&a' in the eval is being compiled, f() is not currently
1013being executed, so its &a is not available for capture.
1014
1015=item *
1016
1017L<"%s" subroutine &%s masks earlier declaration in same %s|perldiag/"%s" subroutine &%s masks earlier declaration in same %s>
1018
1019(W misc) A "my" or "state" subroutine has been redeclared in the
1020current scope or statement, effectively eliminating all access to
1021the previous instance. This is almost always a typographical error.
1022Note that the earlier subroutine will still exist until the end of
1023the scope or until all closure references to it are destroyed.
1024
1025=item *
1026
1027L<The %s feature is experimental|perldiag/"The %s feature is experimental">
1028
1029(S experimental) This warning is emitted if you enable an experimental
1030feature via C<use feature>. Simply suppress the warning if you want
1031to use the feature, but know that in doing so you are taking the risk
1032of using an experimental feature which may change or be removed in a
1033future Perl version:
1034
7a3f436e 1035 no warnings "experimental::lexical_subs";
00785cb7
RS
1036 use feature "lexical_subs";
1037
1038=item *
1039
1040L<sleep(%u) too large|perldiag/"sleep(%u) too large">
1041
1042(W overflow) You called C<sleep> with a number that was larger than it can
1043reliably handle and C<sleep> probably slept for less time than requested.
1044
1045=item *
1046
94b31d3f
RS
1047L<Wide character in setenv|perldiag/"Wide character in %s">
1048
1049Attempts to put wide characters into environment variables via C<%ENV> now
1050provoke this warning.
1051
1052=item *
1053
37133b20
RS
1054"L<Invalid negative number (%s) in chr|perldiag/"Invalid negative number (%s) in chr">"
1055
1056C<chr()> now warns when passed a negative value [perl #83048].
1057
1058=item *
1059
1060"L<Integer overflow in srand|perldiag/"Integer overflow in srand">"
1061
1062C<srand()> now warns when passed a value that doesn't fit in a C<UV> (since the
1063value will be truncated rather than overflowing) [perl #40605].
1064
1065=item *
1066
1067"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">"
1068
1069Running perl with the C<-i> flag now warns if no input files are provided on
1070the command line [perl #113410].
e5ba1bf1
FC
1071
1072=back
1073
1074=head2 Changes to Existing Diagnostics
1075
e5ba1bf1
FC
1076=over 4
1077
1078=item *
1079
0d146223
RS
1080L<$* is no longer supported, and will become a syntax error|perldiag/"$* is no longer supported, and will become a syntax error">
1081
1082The warning that use of C<$*> and C<$#> is no longer supported is now
1083generated for every location that references them. Previously it would fail
1084to be generated if another variable using the same typeglob was seen first
1085(e.g. C<@*> before C<$*>), and would not be generated for the second and
1086subsequent uses. (It's hard to fix the failure to generate warnings at all
1087without also generating them every time, and warning every time is
1088consistent with the warnings that C<$[> used to generate.)
1089
1090=item *
1091
9abd6633
RS
1092The warnings for C<\b{> and C<\B{> were added. They are a deprecation
1093warning which should be turned off by that category. One should not
1094have to turn off regular regexp warnings as well to get rid of these.
e7ae12cf
RS
1095
1096=item *
1097
d268df4d
RS
1098L<Constant(%s): Call to &{$^H{%s}} did not return a defined value|perldiag/Constant(%s): Call to &{$^H{%s}} did not return a defined value>
1099
1100Constant overloading that returns C<undef> results in this error message.
1101For numeric constants, it used to say "Constant(undef)". "undef" has been
1102replaced with the number itself.
1103
1104=item *
1105
f7b06e7f
RS
1106The error produced when a module cannot be loaded now includes a hint that
1107the module may need to be installed: "Can't locate hopping.pm in @INC (you
1108may need to install the hopping module) (@INC contains: ...)"
1109
1110=item *
1111
00785cb7
RS
1112L<vector argument not supported with alpha versions|perldiag/vector argument not supported with alpha versions>
1113
1114This warning was not suppressable, even with C<no warnings>. Now it is
1115suppressible, and has been moved from the "internal" category to the
1116"printf" category.
1117
1118=item *
1119
1120C<< Can't do {n,m} with n > m in regex; marked by <-- HERE in m/%s/ >>
1121
1122This fatal error has been turned into a warning that reads:
1123
1124L<< Quantifier {n,m} with n > m can't match in regex | perldiag/Quantifier {n,m} with n > m can't match in regex >>
1125
1126(W regexp) Minima should be less than or equal to maxima. If you really want
1127your regexp to match something 0 times, just put {0}.
1128
1129=item *
1130
0fef449b
RS
1131The "Runaway prototype" warning that occurs in bizarre cases has been
1132removed as being unhelpful and inconsistent.
1133
1134=item *
1135
1136The "Not a format reference" error has been removed, as the only case in
1137which it could be triggered was a bug.
1138
1139=item *
1140
1141The "Unable to create sub named %s" error has been removed for the same
1142reason.
e5ba1bf1 1143
37133b20
RS
1144=item *
1145
1146The 'Can't use "my %s" in sort comparison' error has been downgraded to a
1147warning, '"my %s" used in sort comparison' (with 'state' instead of 'my'
1148for state variables). In addition, the heuristics for guessing whether
1149lexical $a or $b has been misused have been improved to generate fewer
1150false positives. Lexical $a and $b are no longer disallowed if they are
1151outside the sort block. Also, a named unary or list operator inside the
1152sort block no longer causes the $a or $b to be ignored [perl #86136].
1153
e5ba1bf1
FC
1154=back
1155
1156=head1 Utility Changes
1157
f7b06e7f 1158=head3 L<h2xs>
e5ba1bf1
FC
1159
1160=over 4
1161
1162=item *
1163
f7b06e7f 1164F<h2xs> no longer produces invalid code for empty defines. [perl #20636]
e5ba1bf1
FC
1165
1166=back
1167
1168=head1 Configuration and Compilation
1169
e5ba1bf1
FC
1170=over 4
1171
1172=item *
1173
e7ae12cf
RS
1174Added C<useversionedarchname> option to Configure
1175
1176When set, it includes 'api_versionstring' in 'archname'. E.g.
1177x86_64-linux-5.13.6-thread-multi. It is unset by default.
1178
1179This feature was requested by Tim Bunce, who observed that
1180INSTALL_BASE creates a library structure that does not
1181differentiate by perl version. Instead, it places architecture
1182specific files in "$install_base/lib/perl5/$archname". This makes
1183it difficult to use a common INSTALL_BASE library path with
1184multiple versions of perl.
1185
1186By setting -Duseversionedarchname, the $archname will be
1187distinct for architecture *and* API version, allowing mixed use of
1188INSTALL_BASE.
1189
1190=item *
1191
1192Configure will honour the external C<MAILDOMAIN> environment variable, if set.
1193
1194=item *
1195
1196C<installman> no longer ignores the silent option
1197
1198=item *
1199
1200Both C<META.yml> and C<META.json> files are now included in the distribution.
1201
1202=item *
1203
00785cb7
RS
1204F<Configure> will now correctly detect C<isblank()> when compiling with a C++
1205compiler.
1206
1207=item *
1208
94b31d3f
RS
1209The pager detection in F<Configure> has been improved to allow responses which
1210specify options after the program name, e.g. B</usr/bin/less -R>, if the user
1211accepts the default value. This helps B<perldoc> when handling ANSI escapes
1212[perl #72156].
e5ba1bf1
FC
1213
1214=back
1215
1216=head1 Testing
1217
e5ba1bf1
FC
1218=over 4
1219
1220=item *
1221
0bba4573
RS
1222The test suite now has a section for tests that require very large amounts
1223of memory. These tests won't run by default; they can be enabled by
1224setting the C<PERL_TEST_MEMORY> environment variable to the number of
1225gibibytes of memory that may be safely used.
e5ba1bf1
FC
1226
1227=back
1228
1229=head1 Platform Support
1230
e5ba1bf1
FC
1231=head2 Discontinued Platforms
1232
e5ba1bf1
FC
1233=over 4
1234
d5ed3fc2
RS
1235=item BeOS
1236
1237BeOS was an operating system for personal computers developed by Be Inc,
1238initially for their BeBox hardware. The OS Haiku was written as an open
1239source replacement/continuation for BeOS, and its perl port is current and
1240actively maintained.
1241
94b31d3f 1242=item UTS Global
e5ba1bf1 1243
94b31d3f
RS
1244Support code relating to UTS global has been removed. UTS was a mainframe
1245version of System V created by Amdahl, subsequently sold to UTS Global. The
1246port has not been touched since before Perl 5.8.0, and UTS Global is now
1247defunct.
e5ba1bf1 1248
00785cb7
RS
1249=item VM/ESA
1250
1251Support for VM/ESA has been removed. The port was tested on 2.3.0, which
1252IBM ended service on in March 2002. 2.4.0 ended service in June 2003, and
1253was superseded by Z/VM. The current version of Z/VM is V6.2.0, and scheduled
1254for end of service on 2015/04/30.
1255
f7b06e7f
RS
1256=item MPE/IX
1257
1258Support for MPE/IX has been removed.
1259
7e7c78a1
RS
1260=item EPOC
1261
1262Support code relating to EPOC has been removed. EPOC was a family of
1263operating systems developed by Psion for mobile devices. It was the
1264predecessor of Symbian. The port was last updated in April 2002.
1265
816361ee
RS
1266=item Rhapsody
1267
1268Support for Rhapsody has been removed.
1269
e5ba1bf1
FC
1270=back
1271
1272=head2 Platform-Specific Notes
1273
30bcad58 1274=head3 AIX
e5ba1bf1 1275
30bcad58
RS
1276Configure now always adds C<-qlanglvl=extc99> to the CC flags on AIX when
1277using xlC. This will make it easier to compile a number of XS-based modules
1278that assume C99 [perl #113778].
e5ba1bf1 1279
30bcad58 1280=head3 clang++
e5ba1bf1 1281
0bba4573
RS
1282There is now a workaround for a compiler bug that prevented compiling
1283with clang++ since Perl 5.15.7 [perl #112786].
1284
30bcad58 1285=head3 C++
0bba4573
RS
1286
1287When compiling the Perl core as C++ (which is only semi-supported), the
1288mathom functions are now compiled as C<extern "C">, to ensure proper
1289binary compatibility. (However, binary compatibility isn't generally
1290guaranteed anyway in the situations where this would matter.)
1291
30bcad58
RS
1292=head3 Darwin
1293
1294Stop hardcoding an alignment on 8 byte boundaries to fix builds using
1295-Dusemorebits.
1296
1297=head3 Haiku
1298
1299Perl should now work out of the box on Haiku R1 Alpha 4.
1300
1301=head3 MidnightBSD
1302
1303C<libc_r> was removed from recent versions of MidnightBSD and older versions
1304work better with C<pthread>. Threading is now enabled using C<pthread> which
1305corrects build errors with threading enabled on 0.4-CURRENT.
1306
1307=head3 Solaris
1308
1309In Configure, avoid running sed commands with flags not supported on Solaris.
1310
1311=head3 VMS
1312
1313=over
1314
1315=item *
7e7c78a1
RS
1316
1317Where possible, the case of filenames and command-line arguments is now
1318preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
1319C<DECC$ARGV_PARSE_STYLE> at start-up time. The latter only takes effect
1320when extended parse is enabled in the process from which Perl is run.
1321
30bcad58 1322=item *
e7ae12cf
RS
1323
1324The character set for Extended Filename Syntax (EFS) is now enabled by default
1325on VMS. Among other things, this provides better handling of dots in directory
1326names, multiple dots in filenames,and spaces in filenames. To obtain the old
1327behavior, set the logical name C<DECC$EFS_CHARSET> to C<DISABLE>.
1328
30bcad58 1329=item *
e7ae12cf 1330
30bcad58 1331Fix linking on builds configured with -Dusemymalloc=y.
e7ae12cf 1332
30bcad58 1333=item *
7e7c78a1 1334
30bcad58 1335It should now be possible to compile Perl as C++ on VMS.
7e7c78a1 1336
30bcad58 1337=item *
816361ee 1338
30bcad58
RS
1339All C header files from the top-level directory of the distribution are now
1340installed on VMS, providing consistency with a long-standing practice on other
1341platforms. Previously only a subset were installed, which broke non-core
1342extension builds for extensions that depended on the missing include files.
816361ee 1343
30bcad58 1344=item *
816361ee 1345
30bcad58
RS
1346Quotes are now removed from the command verb (but not the parameters) for
1347commands spawned via C<system>, backticks, or a piped C<open>. Previously,
1348quotes on the verb were passed through to DCL, which would fail to recognize
1349the command. Also, if the verb is actually a path to an image or command
1350procedure on an ODS-5 volume, quoting it now allows the path to contain spaces.
816361ee 1351
30bcad58 1352=item *
00785cb7 1353
30bcad58 1354The B<a2p> build has been fixed for the HP C++ compiler on OpenVMS.
00785cb7 1355
30bcad58 1356=back
00785cb7 1357
30bcad58 1358=head3 Win32
f7b06e7f 1359
30bcad58 1360=over
f7b06e7f 1361
30bcad58 1362=item *
00785cb7 1363
30bcad58
RS
1364Perl can now be built using Microsoft's Visual C++ 2012 compiler by specifying
1365CCTYPE=MSVC110 (or MSVC110FREE if you are using the free Express edition for
1366Windows Desktop) in F<win32/Makefile>.
00785cb7 1367
30bcad58 1368=item *
00785cb7 1369
30bcad58 1370The option to build without USE_SOCKETS_AS_HANDLES has been removed.
00785cb7 1371
30bcad58 1372=item *
00785cb7 1373
30bcad58
RS
1374Fixed a problem where perl could crash while cleaning up threads (including the
1375main thread) in threaded debugging builds on Win32 and possibly other platforms
1376[perl #114496].
00785cb7 1377
30bcad58 1378=item *
0bba4573 1379
30bcad58
RS
1380A rare race condition that would lead to L<sleep|perlfunc/sleep> taking more
1381time than requested, and possibly even hanging, has been fixed [perl #33096].
e5ba1bf1 1382
30bcad58 1383=item *
0fef449b
RS
1384
1385C<link> on Win32 now attempts to set C<$!> to more appropriate values
1386based on the Win32 API error code. [perl #112272]
1387
1388Perl no longer mangles the environment block, e.g. when launching a new
1389sub-process, when the environment contains non-ASCII characters. Known
1390problems still remain, however, when the environment contains characters
1391outside of the current ANSI codepage (e.g. see the item about Unicode in
1392C<%ENV> in L<http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod>).
1393[perl #113536]
1394
30bcad58 1395=item *
37133b20
RS
1396
1397Building perl with some Windows compilers used to fail due to a problem
1398with miniperl's C<glob> operator (which uses the C<perlglob> program)
1399deleting the PATH environment variable [perl #113798].
1400
30bcad58 1401=item *
37133b20 1402
30bcad58
RS
1403A new makefile option, USE_64_BIT_INT, has been added to the Windows
1404makefiles. Set this to "define" when building a 32-bit perl if you want
1405it to use 64-bit integers.
37133b20 1406
30bcad58
RS
1407Machine code size reductions, already made to the DLLs of XS modules in
1408Perl 5.17.2, have now been extended to the perl DLL itself.
94b31d3f 1409
30bcad58
RS
1410Building with VC++ 6.0 was inadvertently broken in Perl 5.17.2 but has
1411now been fixed again.
94b31d3f 1412
30bcad58 1413=back
37133b20 1414
30bcad58 1415=head3 WinCE
37133b20 1416
30bcad58
RS
1417Building on WinCE is now possible once again, although more work is required
1418to fully restore a clean build.
e5ba1bf1
FC
1419
1420=head1 Internal Changes
1421
0bba4573 1422=over
e5ba1bf1 1423
0bba4573 1424=item *
e5ba1bf1 1425
e7ae12cf
RS
1426Synonyms for the misleadingly named C<av_len()> has been created:
1427C<av_top_index()> and C<av_tindex>. All three of these return the
1428number of the highest index in the array, not the number of elements it
1429contains.
816361ee
RS
1430
1431=item *
1432
d268df4d
RS
1433SvUPGRADE() is no longer an expression. Originally this macro (and its
1434underlying function, sv_upgrade()) were documented as boolean, although
1435in reality they always croaked on error and never returned false. In 2005
1436the documentation was updated to specify a void return value, but
1437SvUPGRADE() was left always returning 1 for backwards compatibility. This
1438has now been removed, and SvUPGRADE() is now a statement with no return
1439value.
1440
1441So this is now a syntax error:
1442
1443 if (!SvUPGRADE(sv)) { croak(...); }
1444
1445If you have code like that, simply replace it with
1446
1447 SvUPGRADE(sv);
1448
1449or to to avoid compiler warnings with older perls, possibly
1450
1451 (void)SvUPGRADE(sv);
1452
1453=item *
1454
1455Perl has a new copy-on-write mechanism that allows any SvPOK scalar to be
1456upgraded to a copy-on-write scalar. A reference count on the string buffer
1457is stored in the string buffer itself.
1458
1459This breaks a few XS modules by allowing copy-on-write scalars to go
1460through code paths that never encountered them before.
1461
1462This behaviour can still be disabled by running F<Configure> with
1463B<-Accflags=-DPERL_NO_COW>. This option will probably be removed in Perl
14645.20.
1465
1466=item *
1467
1468Copy-on-write no longer uses the SvFAKE and SvREADONLY flags. Hence,
1469SvREADONLY indicates a true read-only SV.
1470
1471Use the SvIsCOW macro (as before) to identify a copy-on-write scalar.
1472
1473=item *
1474
d268df4d
RS
1475PL_glob_index is gone.
1476
1477=item *
1478
7e7c78a1
RS
1479The private Perl_croak_no_modify has had its context parameter removed. It is
1480now has a void prototype. Users of the public API croak_no_modify remain
1481unaffected.
1482
1483=item *
1484
1485Copy-on-write (shared hash key) scalars are no longer marked read-only.
1486C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
1487true.
1488
1489=item *
1490
1491A new op type, C<OP_PADRANGE> has been introduced. The perl peephole
1492optimiser will, where possible, substitute a single padrange op for a
1493pushmark followed by one or more pad ops, and possibly also skipping list
1494and nextstate ops. In addition, the op can carry out the tasks associated
1495with the RHS of a my(...) = @_ assignment, so those ops may be optimised
1496away too.
1497
1498=item *
1499
f7b06e7f
RS
1500Case-insensitive matching inside a [bracketed] character class with a
1501multi-character fold, no longer excludes one of the possibilities in the
1502circumstances that it used to. [perl #89774].
1503
1504=item *
1505
1506C<PL_formfeed> has been removed.
1507
1508=item *
1509
1510The regular expression engine no longer reads one byte past the end of the
1511target string. While for all internally well-formed scalars this should
1512never have been a problem, this change facilitates clever tricks with
1513string buffers in CPAN modules. [perl #73542]
1514
1515=item *
1516
1517Inside a BEGIN block, C<PL_compcv> now points to the currently-compiling
1518subroutine, rather than the BEGIN block itself.
1519
1520=item *
1521
1522C<mg_length> has been deprecated.
1523
1524=item *
1525
1526C<sv_len> now always returns a byte count and C<sv_len_utf8> a character
1527count. Previously, C<sv_len> and C<sv_len_utf8> were both buggy and would
1528sometimes returns bytes and sometimes characters. C<sv_len_utf8> no longer
1529assumes that its argument is in UTF8. Neither of these creates UTF8 caches
1530for tied or overloaded values or for non-PVs any more.
1531
1532=item *
1533
1534C<sv_mortalcopy> now copies string buffers of shared hash key scalars when
1535called from XS modules [perl #79824].
1536
1537=item *
1538
1539C<RXf_SPLIT> and C<RXf_SKIPWHITE> are no longer used. They are now
1540#defined as 0.
1541
1542=item *
1543
1544The new C<RXf_MODIFIES_VARS> flag can be set by custom regular expression
1545engines to indicate that the execution of the regular expression may cause
1546variables to be modified. This lets C<s///> know to skip certain
1547optimisations. Perl's own regular expression engine sets this flag for the
1548special backtracking verbs that set $REGMARK and $REGERROR.
1549
1550=item *
1551
00785cb7
RS
1552The APIs for accessing lexical pads have changed considerably.
1553
30bcad58
RS
1554C<PADLIST>s are now longer C<AV>s, but their own type instead.
1555C<PADLIST>s now contain a C<PAD> and a C<PADNAMELIST> of C<PADNAME>s,
1556rather than C<AV>s for the pad and the list of pad names. C<PAD>s,
1557C<PADNAMELIST>s, and C<PADNAME>s are to be accessed as such through the
1558newly added pad API instead of the plain C<AV> and C<SV> APIs. See
1559L<perlapi> for details.
00785cb7
RS
1560
1561=item *
1562
1563In the regex API, the numbered capture callbacks are passed an index
1564indicating what match variable is being accessed. There are special
1565index values for the C<$`, $&, $&> variables. Previously the same three
1566values were used to retrieve C<${^PREMATCH}, ${^MATCH}, ${^POSTMATCH}>
1567too, but these have now been assigned three separate values. See
1568L<perlreapi/Numbered capture callbacks>.
1569
1570=item *
1571
1572C<PL_sawampersand> was previously a boolean indicating that any of
1573C<$`, $&, $&> had been seen; it now contains three one-bit flags
1574indicating the presence of each of the variables individually.
1575
00785cb7
RS
1576=item *
1577
0bba4573
RS
1578The C<CV *> typemap entry now supports C<&{}> overloading and typeglobs,
1579just like C<&{...}> [perl #96872].
e5ba1bf1
FC
1580
1581=item *
1582
0bba4573
RS
1583The C<SVf_AMAGIC> flag to indicate overloading is now on the stash, not the
1584object. It is now set automatically whenever a method or @ISA changes, so
1585its meaning has changed, too. It now means "potentially overloaded". When
1586the overload table is calculated, the flag is automatically turned off if
1587there is no overloading, so there should be no noticeable slowdown.
1588
1589The staleness of the overload tables is now checked when overload methods
1590are invoked, rather than during C<bless>.
1591
1592"A" magic is gone. The changes to the handling of the C<SVf_AMAGIC> flag
1593eliminate the need for it.
1594
1595C<PL_amagic_generation> has been removed as no longer necessary. For XS
1596modules, it is now a macro alias to C<PL_na>.
1597
1598The fallback overload setting is now stored in a stash entry separate from
1599overloadedness itself.
1600
1601=item *
1602
1603The character-processing code has been cleaned up in places. The changes
1604should be operationally invisible.
e5ba1bf1 1605
0fef449b
RS
1606=item *
1607
1608The C<study> function was made a no-op in 5.16. It was simply disabled via
1609a C<return> statement; the code was left in place. Now the code supporting
1610what C<study> used to do has been removed.
1611
1612=item *
1613
1614Under threaded perls, there is no longer a separate PV allocated for every
1615COP to store its package name (C<< cop->stashpv >>). Instead, there is an
1616offset (C<< cop->stashoff >>) into the new C<PL_stashpad> array, which
1617holds stash pointers.
1618
1619=item *
1620
1621In the pluggable regex API, the C<regexp_engine> struct has acquired a new
1622field C<op_comp>, which is currently just for perl's internal use, and
1623should be initialised to NULL by other regex plugin modules.
1624
1625=item *
1626
1627A new function C<alloccoptash> has been added to the API, but is considered
1628experimental. See L<perlapi>.
1629
37133b20
RS
1630=item *
1631
1632Perl used to implement get magic in a way that would sometimes hide bugs in
1633code could call mg_get() too many times on magical values. This hiding of
1634errors no longer occurs, so long-standing bugs may become visible now. If
1635you see magic-related errors in XS code, check to make sure it, together
1636with the Perl API functions it uses, calls mg_get() only once on SvGMAGICAL()
1637values.
1638
1639=item *
1640
1641OP allocation for CVs now uses a slab allocator. This simplifies
1642memory management for OPs allocated to a CV, so cleaning up after a
1643compilation error is simpler and safer [perl #111462][perl #112312].
1644
1645=item *
1646
1647PERL_DEBUG_READONLY_OPS has been rewritten to work with the new slab
1648allocator, allowing it to catch more violations than before.
1649
1650=item *
1651
1652The old slab allocator for ops, which was only enabled for PERL_IMPLICIT_SYS
1653and PERL_DEBUG_READONLY_OPS, has been retired.
1654
e5ba1bf1
FC
1655=back
1656
1657=head1 Selected Bug Fixes
1658
94b31d3f
RS
1659=over 4
1660
1661=item *
e5ba1bf1 1662
d29861e7
RS
1663Here-doc terminators no longer require a terminating newline character when
1664they occur at the end of a file. This was already the case at the end of a
1665string eval [perl #65838].
1666
1667=item *
1668
e7ae12cf
RS
1669-DPERL_GLOBAL_STRUCT builds now free the global struct B<after>
1670they've finished using it.
1671
1672=item *
1673
30bcad58
RS
1674A trailing '/' on a path in @INC will no longer have an additional '/'
1675appended.
e7ae12cf
RS
1676
1677=item *
1678
1679The C<:crlf> layer now works when unread data doesn't fit into its own
1680buffer. [perl #112244].
1681
1682=item *
1683
1684C<ungetc()> now handles UTF-8 encoded data. [perl #116322].
1685
1686=item *
1687
816361ee
RS
1688A bug in the core typemap caused any C types that map to the T_BOOL core
1689typemap entry to not be set, updated, or modified when the T_BOOL variable was
1690used in an OUTPUT: section with an exception for RETVAL. T_BOOL in an INPUT:
1691section was not affected. Using a T_BOOL return type for an XSUB (RETVAL)
1692was not affected. A side effect of fixing this bug is, if a T_BOOL is specified
1693in the OUTPUT: section (which previous did nothing to the SV), and a read only
1694SV (literal) is passed to the XSUB, croaks like "Modification of a read-only
1695value attempted" will happen. [perl #115796]
1696
1697=item *
1698
1699On many platforms, providing a directory name as the script name caused perl
1700to do nothing and report success. It should now universally report an error
1701and exit nonzero. [perl #61362]
1702
1703=item *
1704
30bcad58
RS
1705C<sort {undef} ...> under fatal warnings no longer crashes. It had
1706begun crashing in Perl 5.16.
d268df4d
RS
1707
1708=item *
1709
1710Stashes blessed into each other
1711(C<bless \%Foo::, 'Bar'; bless \%Bar::, 'Foo'>) no longer result in double
1712frees. This bug started happening in Perl 5.16.
1713
1714=item *
1715
1716Numerous memory leaks have been fixed, mostly involving fatal warnings and
1717syntax errors.
1718
1719=item *
1720
d268df4d
RS
1721Some failed regular expression matches such as C<'f' =~ /../g> were not
1722resetting C<pos>. Also, "match-once" patterns (C<m?...?g>) failed to reset
1723it, too, when invoked a second time [perl #23180].
1724
1725=item *
1726
1727Accessing C<$&> after a pattern match now works if it had not been seen
1728before the match. I.e., this applies to C<${'&'}> (under C<no strict>) and
1729C<eval '$&'>. The same applies to C<$'> and C<$`> [perl #4289].
1730
1731=item *
1732
1733Several bugs involving C<local *ISA> and C<local *Foo::> causing stale
1734MRO caches have been fixed.
1735
1736=item *
1737
1738Defining a subroutine when its typeglob has been aliased no longer results
1739in stale method caches. This bug was introduced in Perl 5.10.
1740
1741=item *
1742
1743Localising a typeglob containing a subroutine when the typeglob's package
1744has been deleted from its parent stash no longer produces an error. This
1745bug was introduced in Perl 5.14.
1746
1747=item *
1748
1749Under some circumstances, C<local *method=...> would fail to reset method
1750caches upon scope exit.
1751
1752=item *
1753
1754C</[.foo.]/> is no longer an error, but produces a warning (as before) and
1755is treated as C</[.fo]/> [perl #115818].
1756
1757=item *
1758
1759C<goto $tied_var> now calls FETCH before deciding what type of goto
1760(subroutine or label) this is.
1761
1762=item *
1763
1764Renaming packages through glob assignment
1765(C<*Foo:: = *Bar::; *Bar:: = *Baz::>) in combination with C<m?...?> and
1766C<reset> no longer makes threaded builds crash.
1767
1768=item *
1769
d268df4d
RS
1770A number of bugs related to assigning a list to hash have been fixed. Many of
1771these involve lists with repeated keys like C<(1, 1, 1, 1)>.
1772
1773=over 4
1774
1775=item *
1776
1777The expression C<scalar(%h = (1, 1, 1, 1))> now returns C<4>, not C<2>.
1778
1779=item *
1780
1781The return value of C<%h = (1, 1, 1)> in list context was wrong. Previously
1782this would return C<(1, undef, 1)>, now it returns C<(1, undef)>.
1783
1784=item *
1785
1786Perl now issues the same warning on C<($s, %h) = (1, {})> as it does for
1787C<(%h) = ({})>, "Reference found where even-sized list expected".
1788
1789=item *
1790
1791A number of additional edge cases in list assignment to hashes were
1792corrected. For more details see commit 23b7025ebc.
1793
1794=back
1795
1796=item *
1797
f7b06e7f
RS
1798Attributes applied to lexical variables no longer leak memory.
1799[perl #114764]
1800
1801=item *
1802
1803C<dump>, C<goto>, C<last>, C<next>, C<redo> or C<require> followed by a
1804bareword (or version) and then an infix operator is no longer a syntax
1805error. It used to be for those infix operators (like C<+>) that have a
1806different meaning where a term is expected. [perl #105924]
1807
1808=item *
1809
1810C<require a::b . 1> and C<require a::b + 1> no longer produce erroneous
1811ambiguity warnings. [perl #107002]
1812
1813=item *
1814
1815Class method calls are now allowed on any string, and not just strings
1816beginning with an alphanumeric character. [perl #105922]
1817
1818=item *
1819
1820An empty pattern created with C<qr//> used in C<m///> no longer triggers
1821the "empty pattern reuses last pattern" behaviour. [perl #96230]
1822
1823=item *
1824
1825Tying a hash during iteration no longer results in a memory leak.
1826
1827=item *
1828
1829Freeing a tied hash during iteration no longer results in a memory leak.
1830
1831=item *
1832
1833List assignment to a tied array or hash that dies on STORE no longer
1834results in a memory leak.
1835
1836=item *
1837
1838If the hint hash (C<%^H>) is tied, compile-time scope entry (which copies
1839the hint hash) no longer leaks memory if FETCH dies. [perl #107000]
1840
1841=item *
1842
1843Constant folding no longer inappropriately triggers the special
1844C<split " "> behaviour. [perl #94490]
1845
1846=item *
1847
1848C<defined scalar(@array)>, C<defined do { &foo }>, and similar constructs
1849now treat the argument to C<defined> as a simple scalar. [perl #97466]
1850
1851=item *
1852
1853Running a custom debugging that defines no C<*DB::DB> glob or provides a
1854subroutine stub for C<&DB::DB> no longer results in a crash, but an error
1855instead. [perl #114990]
1856
1857=item *
1858
1859C<reset ""> now matches its documentation. C<reset> only resets C<m?...?>
1860patterns when called with no argument. An empty string for an argument now
1861does nothing. (It used to be treated as no argument.) [perl #97958]
1862
1863=item *
1864
1865C<printf> with an argument returning an empty list no longer reads past the
1866end of the stack, resulting in erratic behaviour. [perl #77094]
1867
1868=item *
1869
1870C<--subname> no longer produces erroneous ambiguity warnings.
1871[perl #77240]
1872
1873=item *
1874
1875C<v10> is now allowed as a label or package name. This was inadvertently
1876broken when v-strings were added in Perl 5.6. [perl #56880]
1877
1878=item *
1879
f7b06e7f
RS
1880C<length>, C<pos>, C<substr> and C<sprintf> could be confused by ties,
1881overloading, references and typeglobs if the stringification of such
1882changed the internal representation to or from UTF8. [perl #114410]
1883
1884=item *
1885
1886utf8::encode now calls FETCH and STORE on tied variables. utf8::decode now
1887calls STORE (it was already calling FETCH).
1888
1889=item *
1890
1891C<$tied =~ s/$non_utf8/$utf8/> no longer loops infinitely if the tied
1892variable returns a Latin-1 string, shared hash key scalar, or reference or
1893typeglob that stringifies as ASCII or Latin-1. This is a regression from
18945.12.x.
1895
1896=item *
1897
1898C<s///> without /e is now better at detecting when it needs to forego
1899certain optimisations, fixing some buggy cases:
1900
1901=over
1902
1903=item *
1904
1905Match variables in certain constructs (C<&&>, C<||>, C<..> and others) in
1906the replacement part; e.g., C<s/(.)/$l{$a||$1}/g>. [perl #26986]
1907
1908=item *
1909
1910Aliases to match variables in the replacement.
1911
1912=item *
1913
30bcad58 1914C<$REGERROR> or C<$REGMARK> in the replacement. [perl #49190]
f7b06e7f
RS
1915
1916=item *
1917
1918An empty pattern (C<s//$foo/>) that causes the last-successful pattern to
1919be used, when that pattern contains code blocks that modify the variables
1920in the replacement.
1921
1922=back
1923
1924=item *
1925
1926The taintedness of the replacement string no longer affects the taintedness
1927of the return value of C<s///e>.
1928
1929=item *
1930
1931The C<$|> autoflush variable is created on-the-fly when needed. If this
1932happened (e.g., if it was mentioned in a module or eval) when the
1933currently-selected filehandle was a typeglob with an empty IO slot, it used
1934to crash. [perl #115206]
1935
1936=item *
1937
1938Line numbers at the end of a string eval are no longer off by one.
1939[perl #114658]
1940
1941=item *
1942
1943@INC filters (subroutines returned by subroutines in @INC) that set $_ to a
1944copy-on-write scalar no longer cause the parser to modify that string
1945buffer in place.
1946
1947=item *
1948
1949C<length($object)> no longer returns the undefined value if the object has
1950string overloading that returns undef. [perl #115260]
1951
1952=item *
1953
1954The use of C<PL_stashcache>, the stash name lookup cache for method calls, has
1955been restored,
1956
1957Commit da6b625f78f5f133 in August 2011 inadvertently broke the code that looks
1958up values in C<PL_stashcache>. As it's a only cache, quite correctly everything
1959carried on working without it.
1960
1961=item *
1962
00785cb7
RS
1963The error "Can't localize through a reference" had disappeared in 5.16.0
1964when C<local %$ref> appeared on the last line of an lvalue subroutine.
1965This error disappeared for C<\local %$ref> in perl 5.8.1. It has now
1966been restored.
1967
1968=item *
1969
1970The parsing of here-docs has been improved significantly, fixing several
1971parsing bugs and crashes and one memory leak, and correcting wrong
1972subsequent line numbers under certain conditions.
1973
1974=item *
1975
1976Inside an eval, the error message for an unterminated here-doc no longer
1977has a newline in the middle of it [perl #70836].
1978
1979=item *
1980
1981A substitution inside a substitution pattern (C<s/${s|||}//>) no longer
1982confuses the parser.
1983
1984=item *
1985
1986It may be an odd place to allow comments, but C<s//"" # hello/e> has
1987always worked, I<unless> there happens to be a null character before the
1988first #. Now it works even in the presence of nulls.
1989
1990=item *
1991
1992An invalid range in C<tr///> or C<y///> no longer results in a memory leak.
1993
1994=item *
1995
1996String eval no longer treats a semicolon-delimited quote-like operator at
1997the very end (C<eval 'q;;'>) as a syntax error.
1998
1999=item *
2000
2001C<< warn {$_ => 1} + 1 >> is no longer a syntax error. The parser used to
2002get confused with certain list operators followed by an anonymous hash and
2003then an infix operator that shares its form with a unary operator.
2004
2005=item *
2006
2007C<(caller $n)[6]> (which gives the text of the eval) used to return the
2008actual parser buffer. Modifying it could result in crashes. Now it always
2009returns a copy. The string returned no longer has "\n;" tacked on to the
2010end. The returned text also includes here-doc bodies, which used to be
2011omitted.
2012
2013=item *
2014
2015Reset the utf8 position cache when accessing magical variables to avoid the
2016string buffer and the utf8 position cache getting out of sync
2017[perl #114410].
2018
2019=item *
2020
2021Various cases of get magic being called twice for magical utf8 strings have been
2022fixed.
2023
2024=item *
2025
2026This code (when not in the presence of C<$&> etc)
2027
2028 $_ = 'x' x 1_000_000;
2029 1 while /(.)/;
2030
2031used to skip the buffer copy for performance reasons, but suffered from C<$1>
2032etc changing if the original string changed. That's now been fixed.
2033
2034=item *
2035
2036Perl doesn't use PerlIO anymore to report out of memory messages, as PerlIO
2037might attempt to allocate more memory.
2038
2039=item *
2040
30bcad58
RS
2041In a regular expression, if something is quantified with C<{n,m}> where
2042C<S<n E<gt> m>>, it can't possibly match. Previously this was a fatal
2043error, but now is merely a warning (and that something won't match).
2044[perl #82954].
00785cb7
RS
2045
2046=item *
2047
2048It used to be possible for formats defined in subroutines that have
2049subsequently been undefined and redefined to close over variables in the
2050wrong pad (the newly-defined enclosing sub), resulting in crashes or
2051"Bizarre copy" errors.
2052
2053=item *
2054
2055Redefinition of XSUBs at run time could produce warnings with the wrong
2056line number.
2057
2058=item *
2059
2060The %vd sprintf format does not support version objects for alpha versions.
2061It used to output the format itself (%vd) when passed an alpha version, and
2062also emit an "Invalid conversion in printf" warning. It no longer does,
2063but produces the empty string in the output. It also no longer leaks
2064memory in this case.
2065
2066=item *
2067
00785cb7
RS
2068C<< $obj->SUPER::method >> calls in the main package could fail if the
2069SUPER package had already been accessed by other means.
2070
2071=item *
2072
2073Stash aliasing (C<*foo:: = *bar::>) no longer causes SUPER calls to ignore
2074changes to methods or @ISA or use the wrong package.
2075
2076=item *
2077
2078Method calls on packages whose names end in ::SUPER are no longer treated
2079as SUPER method calls, resulting in failure to find the method.
2080Furthermore, defining subroutines in such packages no longer causes them to
2081be found by SUPER method calls on the containing package [perl #114924].
2082
00785cb7
RS
2083=item *
2084
94b31d3f
RS
2085C<\w> now matches the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D
2086(ZERO WIDTH JOINER). C<\W> no longer matches these. This change is because
2087Unicode corrected their definition of what C<\w> should match.
e5ba1bf1 2088
94b31d3f
RS
2089=item *
2090
2091C<dump LABEL> no longer leaks its label.
2092
2093=item *
2094
2095Constant folding no longer changes the behaviour of functions like C<stat()>
2096and C<truncate()> that can take either filenames or handles.
2097C<stat 1 ? foo : bar> nows treats its argument as a file name (since it is an
2098arbitrary expression), rather than the handle "foo".
2099
2100=item *
2101
2102C<truncate FOO, $len> no longer falls back to treating "FOO" as a file name if
2103the filehandle has been deleted. This was broken in Perl 5.16.0.
2104
2105=item *
2106
2107Subroutine redefinitions after sub-to-glob and glob-to-glob assignments no
2108longer cause double frees or panic messages.
2109
2110=item *
2111
2112C<s///> now turns vstrings into plain strings when performing a substitution,
2113even if the resulting string is the same (C<s/a/a/>).
2114
2115=item *
2116
2117Prototype mismatch warnings no longer erroneously treat constant subs as having
2118no prototype when they actually have "".
2119
2120=item *
2121
2122Constant subroutines and forward declarations no longer prevent prototype
2123mismatch warnings from omitting the sub name.
2124
2125=item *
2126
2127C<undef> on a subroutine now clears call checkers.
2128
2129=item *
2130
2131The C<ref> operator started leaking memory on blessed objects in Perl 5.16.0.
2132This has been fixed [perl #114340].
2133
2134=item *
2135
2136C<use> no longer tries to parse its arguments as a statement, making
2137C<use constant { () };> a syntax error [perl #114222].
2138
2139=item *
2140
2141On debugging builds, "uninitialized" warnings inside formats no longer cause
2142assertion failures.
2143
2144=item *
2145
2146On debugging builds, subroutines nested inside formats no longer cause
2147assertion failures [perl #78550].
2148
2149=item *
2150
2151Formats and C<use> statements are now permitted inside formats.
2152
2153=item *
2154
2155C<print $x> and C<sub { print $x }-E<gt>()> now always produce the same output.
2156It was possible for the latter to refuse to close over $x if the variable was
2157not active; e.g., if it was defined outside a currently-running named
2158subroutine.
2159
2160=item *
2161
2162Similarly, C<print $x> and C<print eval '$x'> now produce the same output.
2163This also allows "my $x if 0" variables to be seen in the debugger [perl
2164#114018].
2165
2166=item *
2167
2168Formats called recursively no longer stomp on their own lexical variables, but
2169each recursive call has its own set of lexicals.
2170
2171=item *
2172
2173Attempting to free an active format or the handle associated with it no longer
2174results in a crash.
2175
2176=item *
2177
2178Format parsing no longer gets confused by braces, semicolons and low-precedence
2179operators. It used to be possible to use braces as format delimiters (instead
2180of C<=> and C<.>), but only sometimes. Semicolons and low-precedence operators
2181in format argument lines no longer confuse the parser into ignoring the line's
2182return value. In format argument lines, braces can now be used for anonymous
2183hashes, instead of being treated always as C<do> blocks.
2184
2185=item *
2186
2187Formats can now be nested inside code blocks in regular expressions and other
2188quoted constructs (C</(?{...})/> and C<qq/${...}/>) [perl #114040].
2189
2190=item *
2191
2192Formats are no longer created after compilation errors.
2193
2194=item *
2195
94b31d3f
RS
2196Under debugging builds, the B<-DA> command line option started crashing in Perl
21975.16.0. It has been fixed [perl #114368].
2198
2199=item *
2200
94b31d3f
RS
2201A potential deadlock scenario involving the premature termination of a pseudo-
2202forked child in a Windows build with ithreads enabled has been fixed. This
2203resolves the common problem of the F<t/op/fork.t> test hanging on Windows [perl
2204#88840].
2205
2206=item *
2207
2208The microperl build, broken since Perl 5.15.7, has now been restored.
2209
2210=item *
2211
2212The code which generates errors from C<require()> could potentially read one or
2213two bytes before the start of the filename for filenames less than three bytes
2214long and ending C</\.p?\z/>. This has now been fixed. Note that it could
2215never have happened with module names given to C<use()> or C<require()> anyway.
2216
2217=item *
2218
2219The handling of pathnames of modules given to C<require()> has been made
2220thread-safe on VMS.
2221
2222=item *
2223
94b31d3f
RS
2224A bug in the compilation of a C</(?{})/> expression which affected the TryCatch
2225test suite has been fixed [perl #114242].
2226
2227=item *
2228
94b31d3f
RS
2229Pod can now be nested in code inside a quoted construct outside of a string
2230eval. This used to work only within string evals [perl #114040].
e5ba1bf1
FC
2231
2232=item *
2233
0bba4573
RS
2234C<goto ''> now looks for an empty label, producing the "goto must have
2235label" error message, instead of exiting the program [perl #111794].
e5ba1bf1 2236
0bba4573 2237=item *
e5ba1bf1 2238
0bba4573
RS
2239C<goto "\0"> now dies with "Can't find label" instead of "goto must have
2240label".
e5ba1bf1 2241
0bba4573 2242=item *
e5ba1bf1 2243
0bba4573
RS
2244The C function C<hv_store> used to result in crashes when used on C<%^H>
2245[perl #111000].
e5ba1bf1 2246
0bba4573
RS
2247=item *
2248
2249A call checker attached to a closure prototype via C<cv_set_call_checker>
2250is now copied to closures cloned from it. So C<cv_set_call_checker> now
2251works inside an attribute handler for a closure.
e5ba1bf1
FC
2252
2253=item *
2254
0bba4573
RS
2255Writing to C<$^N> used to have no effect. Now it croaks with "Modification
2256of a read-only value" by default, but that can be overridden by a custom
2257regular expression engine, as with C<$1> [perl #112184].
2258
23dd6e2e
FC
2259=item *
2260
0bba4573
RS
2261C<undef> on a control character glob (C<undef *^H>) no longer emits an
2262erroneous warning about ambiguity [perl #112456].
23dd6e2e 2263
0bba4573
RS
2264=item *
2265
2266For efficiency's sake, many operators and built-in functions return the
2267same scalar each time. Lvalue subroutines and subroutines in the CORE::
2268namespace were allowing this implementation detail to leak through.
2269C<print &CORE::uc("a"), &CORE::uc("b")> used to print "BB". The same thing
2270would happen with an lvalue subroutine returning the return value of C<uc>.
2271Now the value is copied in such cases.
23dd6e2e
FC
2272
2273=item *
2274
0bba4573
RS
2275C<method {}> syntax with an empty block or a block returning an empty list
2276used to crash or use some random value left on the stack as its invocant.
2277Now it produces an error.
b92848b5 2278
0f023b5a
FC
2279=item *
2280
0bba4573 2281C<vec> now works with extremely large offsets (E<gt>2 GB) [perl #111730].
0f023b5a
FC
2282
2283=item *
2284
0bba4573
RS
2285Changes to overload settings now take effect immediately, as do changes to
2286inheritance that affect overloading. They used to take effect only after
2287C<bless>.
2288
2289Objects that were created before a class had any overloading used to remain
2290non-overloaded even if the class gained overloading through C<use overload>
2291or @ISA changes, and even after C<bless>. This has been fixed
2292[perl #112708].
c53e3a75
FC
2293
2294=item *
2295
0bba4573 2296Classes with overloading can now inherit fallback values.
c53e3a75
FC
2297
2298=item *
2299
0bba4573
RS
2300Overloading was not respecting a fallback value of 0 if there were
2301overloaded objects on both sides of an assignment operator like C<+=>
2302[perl #111856].
0f023b5a
FC
2303
2304=item *
2305
0bba4573
RS
2306C<pos> now croaks with hash and array arguments, instead of producing
2307erroneous warnings.
0f023b5a
FC
2308
2309=item *
2310
0bba4573
RS
2311C<while(each %h)> now implies C<while(defined($_ = each %h))>, like
2312C<readline> and C<readdir>.
0f023b5a 2313
0bba4573
RS
2314=item *
2315
2316Subs in the CORE:: namespace no longer crash after C<undef *_> when called
2317with no argument list (C<&CORE::time> with no parentheses).
2318
2319=item *
2320
0bba4573
RS
2321C<unpack> no longer produces the "'/' must follow a numeric type in unpack"
2322error when it is the data that are at fault [perl #60204].
2323
2324=item *
2325
2326C<join> and C<"@array"> now call FETCH only once on a tied C<$">
2327[perl #8931].
2328
2329=item *
2330
2331Some subroutine calls generated by compiling core ops affected by a
2332C<CORE::GLOBAL> override had op checking performed twice. The checking
2333is always idempotent for pure Perl code, but the double checking can
2334matter when custom call checkers are involved.
2335
2336=item *
2337
2338A race condition used to exist around fork that could cause a signal sent to
2339the parent to be handled by both parent and child. Signals are now blocked
2340briefly around fork to prevent this from happening [perl #82580].
e5ba1bf1 2341
0fef449b
RS
2342=item *
2343
2344The implementation of code blocks in regular expressions, such as C<(?{})>
2345and C<(??{})>, has been heavily reworked to eliminate a whole slew of bugs.
2346The main user-visible changes are:
2347
2348=over 4
2349
2350=item *
2351
2352Code blocks within patterns are now parsed in the same pass as the
2353surrounding code; in particular it is no longer necessary to have balanced
2354braces: this now works:
2355
2356 /(?{ $x='{' })/
2357
2358This means that this error message is longer generated:
2359
2360 Sequence (?{...}) not terminated or not {}-balanced in regex
2361
2362but a new error may be seen:
2363
2364 Sequence (?{...}) not terminated with ')'
2365
2366In addition, literal code blocks within run-time patterns are only
2367compiled once, at perl compile-time:
2368
2369 for my $p (...) {
2370 # this 'FOO' block of code is compiled once,
2371 # at the same time as the surrounding 'for' loop
2372 /$p{(?{FOO;})/;
2373 }
2374
2375=item *
2376
2377Lexical variables are now sane as regards scope, recursion and closure
2378behavior. In particular, C</A(?{B})C/> behaves (from a closure viewpoint)
2379exactly like C</A/ && do { B } && /C/>, while C<qr/A(?{B})C/> is like
2380C<sub {/A/ && do { B } && /C/}>. So this code now works how you might
2381expect, creating three regexes that match 0, 1, and 2:
2382
2383 for my $i (0..2) {
2384 push @r, qr/^(??{$i})$/;
2385 }
2386 "1" =~ $r[1]; # matches
2387
2388=item *
2389
2390The C<use re 'eval'> pragma is now only required for code blocks defined
2391at runtime; in particular in the following, the text of the C<$r> pattern is
2392still interpolated into the new pattern and recompiled, but the individual
2393compiled code-blocks within C<$r> are reused rather than being recompiled,
2394and C<use re 'eval'> isn't needed any more:
2395
2396 my $r = qr/abc(?{....})def/;
2397 /xyz$r/;
2398
2399=item *
2400
2401Flow control operators no longer crash. Each code block runs in a new
2402dynamic scope, so C<next> etc. will not see
2403any enclosing loops. C<return> returns a value
2404from the code block, not from any enclosing subroutine.
2405
2406=item *
2407
2408Perl normally caches the compilation of run-time patterns, and doesn't
2409recompile if the pattern hasn't changed, but this is now disabled if
2410required for the correct behavior of closures. For example:
2411
2412 my $code = '(??{$x})';
2413 for my $x (1..3) {
2414 # recompile to see fresh value of $x each time
2415 $x =~ /$code/;
2416 }
2417
0fef449b
RS
2418=item *
2419
2420The C</msix> and C<(?msix)> etc. flags are now propagated into the return
2421value from C<(??{})>; this now works:
2422
2423 "AB" =~ /a(??{'b'})/i;
2424
2425=item *
2426
2427Warnings and errors will appear to come from the surrounding code (or for
2428run-time code blocks, from an eval) rather than from an C<re_eval>:
2429
2430 use re 'eval'; $c = '(?{ warn "foo" })'; /$c/;
2431 /(?{ warn "foo" })/;
2432
2433formerly gave:
2434
2435 foo at (re_eval 1) line 1.
2436 foo at (re_eval 2) line 1.
2437
2438and now gives:
2439
2440 foo at (eval 1) line 1.
2441 foo at /some/prog line 2.
2442
2443=back
2444
2445=item *
2446
2447Perl now works as well as can be expected on all releases of Unicode so
2448far. In v5.16, it worked on Unicodes 6.0 and 6.1, but there were
2449various bugs for earlier releases; the older the release the more
2450problems.
2451
2452=item *
2453
2454C<vec> no longer produces "uninitialized" warnings in lvalue context
2455[perl #9423].
2456
2457=item *
2458
2459An optimization involving fixed strings in regular expressions could cause
2460a severe performance penalty in edge cases. This has been fixed
2461[perl #76546].
2462
2463=item *
2464
2465In certain cases, including empty subpatterns within a regular expression (such
2466as C<(?:)> or C<(?:|)>) could disable some optimizations. This has been fixed.
2467
2468=item *
2469
2470The "Can't find an opnumber" message that C<prototype> produces when passed
2471a string like "CORE::nonexistent_keyword" now passes UTF-8 and embedded
2472NULs through unchanged [perl #97478].
2473
2474=item *
2475
2476C<prototype> now treats magical variables like C<$1> the same way as
2477non-magical variables when checking for the CORE:: prefix, instead of
2478treating them as subroutine names.
2479
2480=item *
2481
2482Under threaded perls, a runtime code block in a regular expression could
2483corrupt the package name stored in the op tree, resulting in bad reads
2484in C<caller>, and possibly crashes [perl #113060].
2485
2486=item *
2487
2488Referencing a closure prototype (C<\&{$_[1]}> in an attribute handler for a
2489closure) no longer results in a copy of the subroutine (or assertion
2490failures on debugging builds).
2491
2492=item *
2493
2494C<eval '__PACKAGE__'> now returns the right answer on threaded builds if
2495the current package has been assigned over (as in
2496C<*ThisPackage:: = *ThatPackage::>) [perl #78742].
2497
2498=item *
2499
2500If a package is deleted by code that it calls, it is possible for C<caller>
2501to see a stack frame belonging to that deleted package. C<caller> could
2502crash if the stash's memory address was reused for a scalar and a
2503substitution was performed on the same scalar [perl #113486].
2504
2505=item *
2506
2507C<UNIVERSAL::can> no longer treats its first argument differently
2508depending on whether it is a string or number internally.
2509
2510=item *
2511
2512C<open> with C<< <& >> for the mode checks to see whether the third argument is
2513a number, in determining whether to treat it as a file descriptor or a handle
2514name. Magical variables like C<$1> were always failing the numeric check and
2515being treated as handle names.
2516
2517=item *
2518
2519C<warn>'s handling of magical variables (C<$1>, ties) has undergone several
2520fixes. C<FETCH> is only called once now on a tied argument or a tied C<$@>
2521[perl #97480]. Tied variables returning objects that stringify as "" are
2522no longer ignored. A tied C<$@> that happened to return a reference the
2523I<previous> time it was used is no longer ignored.
2524
2525=item *
2526
2527C<warn ""> now treats C<$@> with a number in it the same way, regardless of
2528whether it happened via C<$@=3> or C<$@="3">. It used to ignore the
2529former. Now it appends "\t...caught", as it has always done with
2530C<$@="3">.
2531
2532=item *
2533
2534Numeric operators on magical variables (e.g., S<C<$1 + 1>>) used to use
2535floating point operations even where integer operations were more appropriate,
2536resulting in loss of accuracy on 64-bit platforms [perl #109542].
2537
2538=item *
2539
2540Unary negation no longer treats a string as a number if the string happened
2541to be used as a number at some point. So, if C<$x> contains the string "dogs",
2542C<-$x> returns "-dogs" even if C<$y=0+$x> has happened at some point.
2543
2544=item *
2545
2546In Perl 5.14, C<-'-10'> was fixed to return "10", not "+10". But magical
2547variables (C<$1>, ties) were not fixed till now [perl #57706].
2548
2549=item *
2550
2551Unary negation now treats strings consistently, regardless of the internal
2552C<UTF8> flag.
2553
2554=item *
2555
2556A regression introduced in Perl v5.16.0 involving
2557C<tr/I<SEARCHLIST>/I<REPLACEMENTLIST>/> has been fixed. Only the first
2558instance is supposed to be meaningful if a character appears more than
2559once in C<I<SEARCHLIST>>. Under some circumstances, the final instance
2560was overriding all earlier ones. [perl #113584]
2561
2562=item *
2563
2564Regular expressions like C<qr/\87/> previously silently inserted a NUL
2565character, thus matching as if it had been written C<qr/\00087/>. Now it
2566matches as if it had been written as C<qr/87/>, with a message that the
2567sequence C<"\8"> is unrecognized.
2568
2569=item *
2570
2571C<__SUB__> now works in special blocks (C<BEGIN>, C<END>, etc.).
2572
2573=item *
2574
2575Thread creation on Windows could theoretically result in a crash if done
2576inside a C<BEGIN> block. It still does not work properly, but it no longer
2577crashes [perl #111610].
2578
2579=item *
2580
2581C<\&{''}> (with the empty string) now autovivifies a stub like any other
2582sub name, and no longer produces the "Unable to create sub" error
2583[perl #94476].
2584
37133b20
RS
2585=item *
2586
2587A regression introduced in v5.14.0 has been fixed, in which some calls
2588to the C<re> module would clobber C<$_> [perl #113750].
2589
2590=item *
2591
2592C<do FILE> now always either sets or clears C<$@>, even when the file can't be
2593read. This ensures that testing C<$@> first (as recommended by the
2594documentation) always returns the correct result.
2595
2596=item *
2597
2598The array iterator used for the C<each @array> construct is now correctly
2599reset when C<@array> is cleared (RT #75596). This happens for example when the
2600array is globally assigned to, as in C<@array = (...)>, but not when its
2601B<values> are assigned to. In terms of the XS API, it means that C<av_clear()>
2602will now reset the iterator.
2603
2604This mirrors the behaviour of the hash iterator when the hash is cleared.
2605
2606=item *
2607
2608C<< $class->can >>, C<< $class->isa >>, and C<< $class->DOES >> now return
2609correct results, regardless of whether that package referred to by C<$class>
2610exists [perl #47113].
2611
2612=item *
2613
2614Arriving signals no longer clear C<$@> [perl #45173].
2615
2616=item *
2617
2618Allow C<my ()> declarations with an empty variable list [perl #113554].
2619
2620=item *
2621
2622During parsing, subs declared after errors no longer leave stubs
2623[perl #113712].
2624
2625=item *
2626
2627Closures containing no string evals no longer hang on to their containing
2628subroutines, allowing variables closed over by outer subroutines to be
2629freed when the outer sub is freed, even if the inner sub still exists
2630[perl #89544].
2631
2632=item *
2633
2634Duplication of in-memory filehandles by opening with a "<&=" or ">&=" mode
2635stopped working properly in 5.16.0. It was causing the new handle to
2636reference a different scalar variable. This has been fixed [perl #113764].
2637
2638=item *
2639
2640C<qr//> expressions no longer crash with custom regular expression engines
2641that do not set C<offs> at regular expression compilation time
2642[perl #112962].
2643
2644=item *
2645
2646C<delete local> no longer crashes with certain magical arrays and hashes
2647[perl #112966].
2648
2649=item *
2650
2651C<local> on elements of certain magical arrays and hashes used not to
2652arrange to have the element deleted on scope exit, even if the element did
2653not exist before C<local>.
2654
2655=item *
2656
2657C<scalar(write)> no longer returns multiple items [perl #73690].
2658
2659=item *
2660
2661String to floating point conversions no longer misparse certain strings under
2662C<use locale> [perl #109318].
2663
2664=item *
2665
2666C<@INC> filters that die no longer leak memory [perl #92252].
2667
2668=item *
2669
2670The implementations of overloaded operations are now called in the correct
2671context. This allows, among other things, being able to properly override
2672C<< <> >> [perl #47119].
2673
2674=item *
2675
2676Specifying only the C<fallback> key when calling C<use overload> now behaves
2677properly [perl #113010].
2678
2679=item *
2680
2681C<< sub foo { my $a = 0; while ($a) { ... } } >> and
2682C<< sub foo { while (0) { ... } } >> now return the same thing [perl #73618].
2683
2684=item *
2685
37133b20
RS
2686String negation now behaves the same under C<use integer;> as it does
2687without [perl #113012].
2688
2689=item *
2690
2691C<chr> now returns the Unicode replacement character (U+FFFD) for -1,
2692regardless of the internal representation. -1 used to wrap if the argument
2693was tied or a string internally.
2694
2695=item *
2696
2697Using a C<format> after its enclosing sub was freed could crash as of
2698perl 5.12.0, if the format referenced lexical variables from the outer sub.
2699
2700=item *
2701
2702Using a C<format> after its enclosing sub was undefined could crash as of
2703perl 5.10.0, if the format referenced lexical variables from the outer sub.
2704
2705=item *
2706
2707Using a C<format> defined inside a closures, which format references
2708lexical variables from outside, never really worked unless the C<write>
2709call was directly inside the closure. In 5.10.0 it even started crashing.
2710Now the copy of that closure nearest the top of the call stack is used to
2711find those variables.
2712
2713=item *
2714
2715Formats that close over variables in special blocks no longer crash if a
2716stub exists with the same name as the special block before the special
2717block is compiled.
2718
2719=item *
2720
2721The parser no longer gets confused, treating C<eval foo ()> as a syntax
2722error if preceded by C<print;> [perl #16249].
2723
2724=item *
2725
2726The return value of C<syscall> is no longer truncated on 64-bit platforms
2727[perl #113980].
2728
2729=item *
2730
2731Constant folding no longer causes C<print 1 ? FOO : BAR> to print to the
2732FOO handle [perl #78064].
2733
2734=item *
2735
2736C<do subname> now calls the named subroutine and uses the file name it
2737returns, instead of opening a file named "subname".
2738
2739=item *
2740
2741Subroutines looked up by rv2cv check hooks (registered by XS modules) are
2742now taken into consideration when determining whether C<foo bar> should be
2743the sub call C<foo(bar)> or the method call C<< "bar"->foo >>.
2744
2745=item *
2746
2747C<CORE::foo::bar> is no longer treated specially, allowing global overrides
2748to be called directly via C<CORE::GLOBAL::uc(...)> [perl #113016].
2749
2750=item *
2751
2752Calling an undefined sub whose typeglob has been undefined now produces the
2753customary "Undefined subroutine called" error, instead of "Not a CODE
2754reference".
2755
2756=item *
2757
2758Two bugs involving @ISA have been fixed. C<*ISA = *glob_without_array> and
2759C<undef *ISA; @{*ISA}> would prevent future modifications to @ISA from
2760updating the internal caches used to look up methods. The
2761*glob_without_array case was a regression from Perl 5.12.
2762
2763=item *
2764
2765Regular expression optimisations sometimes caused C<$> with C</m> to
2766produce failed or incorrect matches [perl #114068].
2767
2768=item *
2769
2770C<__SUB__> now works in a C<sort> block when the enclosing subroutine is
2771predeclared with C<sub foo;> syntax [perl #113710].
2772
2773=item *
2774
2775Unicode properties only apply to Unicode code points, which leads to
2776some subtleties when regular expressions are matched against
2777above-Unicode code points. There is a warning generated to draw your
2778attention to this. However, this warning was being generated
2779inappropriately in some cases, such as when a program was being parsed.
2780Non-Unicode matches such as C<\w> and C<[:word;]> should not generate the
2781warning, as their definitions don't limit them to apply to only Unicode
2782code points. Now the message is only generated when matching against
2783C<\p{}> and C<\P{}>. There remains a bug, [perl #114148], for the very
2784few properties in Unicode that match just a single code point. The
2785warning is not generated if they are matched against an above-Unicode
2786code point.
2787
7e7c78a1
RS
2788=item *
2789
2790Uninitialized warnings mentioning hash elements would only mention the
2791element name if it was not in the first bucket of the hash, due to an
2792off-by-one error.
2793
2794=item *
2795
2796A regular expression optimizer bug could cause multiline "^" to behave
2797incorrectly in the presence of line breaks, such that
2798C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].
2799
2800=item *
2801
2802Failed C<fork> in list context no longer currupts the stack.
2803C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
2804if the C<fork> call failed.
2805
2806=item *
2807
2808Numerous memory leaks have been fixed, mostly involving tied variables that
2809die, regular expression character classes and code blocks, and syntax
2810errors.
2811
2812=item *
2813
2814Assigning a regular expression (C<${qr//}>) to a variable that happens to
2815hold a floating point number no longer causes assertion failures on
2816debugging builds.
2817
2818=item *
2819
2820Assigning a regular expression to a scalar containing a number no longer
2821causes subsequent nummification to produce random numbers.
2822
2823=item *
2824
2825Assigning a regular expression to a magic variable no longer wipes away the
2826magic. This is a regression from 5.10.
2827
2828=item *
2829
2830Assigning a regular expression to a blessed scalar no longer results in
2831crashes. This is also a regression from 5.10.
2832
2833=item *
2834
2835Regular expression can now be assigned to tied hash and array elements with
2836flattening into strings.
2837
2838=item *
2839
2840Nummifying a regular expression no longer results in an uninitialized
2841warning.
2842
2843=item *
2844
2845Negative array indices no longer cause EXISTS methods of tied variables to
2846be ignored. This is a regression from 5.12.
2847
2848=item *
2849
2850Negative array indices no longer result in crashes on arrays tied to
2851non-objects.
2852
2853=item *
2854
7e7c78a1
RS
2855C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF8 if the
2856left-hand scalar happened to have produced a UTF8 string the last time
2857overloading was invoked.
2858
2859=item *
2860
2861C<goto &sub> now uses the current value of @_, instead of using the array
2862the subroutine was originally called with. This means
2863C<local @_ = (...); goto &sub> now works [perl #43077].
2864
2865=item *
2866
2867If a debugger is invoked recursively, it no longer stomps on its own
2868lexical variables. Formerly under recursion all calls would share the same
2869set of lexical variables [perl #115742].
2870
2871=item *
2872
2873C<*_{ARRAY}> returned from a subroutine no longer spontaneously
2874becomes empty.
2875
e5ba1bf1
FC
2876=back
2877
0bba4573 2878=head1 Known Problems
e5ba1bf1 2879
0bba4573
RS
2880=over 4
2881
2882=item *
2883
30bcad58 2884XXX: the imperfect behavior of the ** deprecation
0bba4573
RS
2885
2886=back
e5ba1bf1
FC
2887
2888=head1 Acknowledgements
2889
2890XXX Generate this with:
2891
de3d8d88 2892 perl Porting/acknowledgements.pl v5.17.12..HEAD
e5ba1bf1
FC
2893
2894=head1 Reporting Bugs
2895
2896If you find what you think is a bug, you might check the articles recently
2897posted to the comp.lang.perl.misc newsgroup and the perl bug database at
2898http://rt.perl.org/perlbug/ . There may also be information at
2899http://www.perl.org/ , the Perl Home Page.
2900
2901If you believe you have an unreported bug, please run the L<perlbug> program
2902included with your release. Be sure to trim your bug down to a tiny but
2903sufficient test case. Your bug report, along with the output of C<perl -V>,
2904will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
2905
2906If the bug you are reporting has security implications, which make it
2907inappropriate to send to a publicly archived mailing list, then please send it
2908to perl5-security-report@perl.org. This points to a closed subscription
2909unarchived mailing list, which includes all the core committers, who will be
2910able to help assess the impact of issues, figure out a resolution, and help
2911co-ordinate the release of patches to mitigate or fix the problem across all
2912platforms on which Perl is supported. Please only use this address for
2913security issues in the Perl core, not for modules independently distributed on
2914CPAN.
2915
2916=head1 SEE ALSO
2917
2918The F<Changes> file for an explanation of how to view exhaustive details on
2919what changed.
2920
2921The F<INSTALL> file for how to build Perl.
2922
2923The F<README> file for general stuff.
2924
2925The F<Artistic> and F<Copying> files for copyright information.
2926
2927=cut