5 perl5170delta - what is new for perl v5.17.0
9 This document describes differences between the 5.16.0 release and
12 If you are upgrading from an earlier release such as 5.16.0, first read
13 L<perl5160delta>, which describes differences between 5.14.0 and
16 =head1 Incompatible Changes
18 =head2 qw(...) can no longer be used as parentheses
20 C<qw> lists used to fool the parser into thinking they were always
21 surrounded by parentheses. This permitted some surprising constructions
22 such as C<foreach $x qw(a b c) {...}>, which should really be written
23 C<foreach $x (qw(a b c)) {...}>. These would sometimes get the lexer into
24 the wrong state, so they didn't fully work, and the similar C<foreach qw(a
25 b c) {...}> that one might expect to be permitted never worked at all.
27 This side effect of C<qw> has now been abolished. It has been deprecated
28 since Perl 5.13.11. It is now necessary to use real parentheses
29 everywhere that the grammar calls for them.
31 =head2 C<\s> in regular expressions now matches a Vertical Tab (experimental)
33 This is an experiment early in the development cycle to see what
34 repercussions arise from this change. It may well be that we decide
35 to require a C<"use feature"> to activate this behavior. Because
36 of the experimental nature of this, which may be reversed, the
37 documentation has not been changed to reflect it.
41 =head2 Unescaped braces in regexps
43 Literal unescaped C<{> in regular expressions is now deprecated. Every
44 brace character should be either escaped (by a preceding backslash) or
45 part of a construct where it's a metacharacter. This catches likely typos
46 such as C</f{,3}/>. It will also allow braces to be used in the future
47 to delimit parameters to metacharacters that currently take no parameters.
49 =head1 Performance Enhancements
55 Filetest ops manage the stack in a fractionally more efficient manner.
59 Globs used in a numeric context are now numerified directly in most cases,
60 rather than being numerified via stringification.
64 =head1 Modules and Pragmata
66 =head2 Updated Modules and Pragmata
72 L<B> has been upgraded from version 1.34 to 1.35.
74 The C<stashlen> method of COPs has been added. This provides access to an
75 internal field added in perl 5.16 under threaded builds [perl #113034].
79 L<ExtUtils::ParseXS> has been upgraded from version 3.16 to 3.17.
81 The generated C code now avoids unnecessarily incrementing
82 C<PL_amagic_generation> on Perl versions where it's done automatically
83 (or on current Perl where the variable no longer exists).
87 L<File::DosGlob> has been upgraded from version 1.06 to 1.07.
89 Small documentation and comment fixes.
93 L<File::Find> has been upgraded from version 1.20 to 1.21.
95 Individual files may now appear in list of directories to be searched
100 L<File::stat> has been upgraded from version 1.05 to 1.06.
102 C<File::stat> ignores the L<filetest> pragma, and warns when used in
103 combination therewith. But it was not warning for C<-r>. This has been
104 fixed [perl #111640].
106 C<-p> now works, and does not return false for pipes [perl #111638].
110 L<Hash::Util> has been upgraded from version 0.11 to 0.12.
112 C<hash_unlocked> and C<hashref_unlocked> now returns true if the hash is
113 unlocked, instead of always returning false [perl #112126].
115 C<hash_unlocked>, C<hashref_unlocked>, C<lock_hash_recurse> and
116 C<unlock_hash_recurse> are now exportable [perl #112126].
118 Two new functions, C<hash_locked> and C<hashref_locked>, have been added.
119 Oddly enough, these two functions were already exported, even though they
120 did not exist [perl #112126].
124 L<Module::CoreList> has been upgraded from version 2.66 to 2.67.
128 L<overload> has been upgraded from version 1.18 to 1.19.
130 C<no overload> now warns for invalid arguments, just like C<use overload>.
134 L<Pod::Functions> has been upgraded from version 1.05 to 1.06.
136 Typo fix in generated documentation.
140 L<Storable> has been upgraded from version 2.34 to 2.35.
142 Modifying C<$_[0]> within C<STORABLE_freeze> no longer results in crashes
145 An object whose class implements C<STORABLE_attach> is now thawed only once
146 when there are multiple references to it in the structure being thawed
151 L<utf8> has been upgraded from version 1.09 to 1.10.
153 Some documentation has been clarified.
157 =head2 Removed Modules and Pragmata
163 L<Version::Requirements> has been removed from the core distribution. It is
164 available under a different name: L<CPAN::Meta::Requirements>.
170 =head2 Changes to Existing Documentation
178 Now explicitly documents the behaviour of hash initializer lists that
179 contain duplicate keys.
189 The explanation of symbolic references being prevented by "strict refs"
190 now doesn't assume that the reader knows what symbolic references are.
200 The return value of C<pipe> is now documented.
206 The following additions or changes have been made to diagnostic output,
207 including warnings and fatal error messages. For the complete list of
208 diagnostic messages, see L<perldiag>.
210 =head2 New Diagnostics
218 "L<Unescaped left brace in regex is deprecated, passed
219 through|perldiag/"Unescaped left brace in regex is deprecated, passed
220 through">" is a new deprecation warning. See L</Unescaped braces in
231 The test suite now has a section for tests that require very large amounts
232 of memory. These tests won't run by default; they can be enabled by
233 setting the C<PERL_TEST_MEMORY> environment variable to the number of
234 gibibytes of memory that may be safely used.
238 =head1 Platform Support
240 =head2 Platform-Specific Notes
246 There is now a workaround for a compiler bug that prevented compiling
247 with clang++ since Perl 5.15.7 [perl #112786].
251 When compiling the Perl core as C++ (which is only semi-supported), the
252 mathom functions are now compiled as C<extern "C">, to ensure proper
253 binary compatibility. (However, binary compatibility isn't generally
254 guaranteed anyway in the situations where this would matter.)
258 It should now be possible to compile Perl as C++ on VMS.
262 =head1 Internal Changes
268 The C<CV *> typemap entry now supports C<&{}> overloading and typeglobs,
269 just like C<&{...}> [perl #96872].
273 The C<SVf_AMAGIC> flag to indicate overloading is now on the stash, not the
274 object. It is now set automatically whenever a method or @ISA changes, so
275 its meaning has changed, too. It now means "potentially overloaded". When
276 the overload table is calculated, the flag is automatically turned off if
277 there is no overloading, so there should be no noticeable slowdown.
279 The staleness of the overload tables is now checked when overload methods
280 are invoked, rather than during C<bless>.
282 "A" magic is gone. The changes to the handling of the C<SVf_AMAGIC> flag
283 eliminate the need for it.
285 C<PL_amagic_generation> has been removed as no longer necessary. For XS
286 modules, it is now a macro alias to C<PL_na>.
288 The fallback overload setting is now stored in a stash entry separate from
289 overloadedness itself.
293 The character-processing code has been cleaned up in places. The changes
294 should be operationally invisible.
298 =head1 Selected Bug Fixes
304 C<goto ''> now looks for an empty label, producing the "goto must have
305 label" error message, instead of exiting the program [perl #111794].
309 C<goto "\0"> now dies with "Can't find label" instead of "goto must have
314 The C function C<hv_store> used to result in crashes when used on C<%^H>
319 A call checker attached to a closure prototype via C<cv_set_call_checker>
320 is now copied to closures cloned from it. So C<cv_set_call_checker> now
321 works inside an attribute handler for a closure.
325 Writing to C<$^N> used to have no effect. Now it croaks with "Modification
326 of a read-only value" by default, but that can be overridden by a custom
327 regular expression engine, as with C<$1> [perl #112184].
331 C<undef> on a control character glob (C<undef *^H>) no longer emits an
332 erroneous warning about ambiguity [perl #112456].
336 For efficiency's sake, many operators and built-in functions return the
337 same scalar each time. Lvalue subroutines and subroutines in the CORE::
338 namespace were allowing this implementation detail to leak through.
339 C<print &CORE::uc("a"), &CORE::uc("b")> used to print "BB". The same thing
340 would happen with an lvalue subroutine returning the return value of C<uc>.
341 Now the value is copied in such cases.
345 C<method {}> syntax with an empty block or a block returning an empty list
346 used to crash or use some random value left on the stack as its invocant.
347 Now it produces an error.
351 C<vec> now works with extremely large offsets (E<gt>2 GB) [perl #111730].
355 Changes to overload settings now take effect immediately, as do changes to
356 inheritance that affect overloading. They used to take effect only after
359 Objects that were created before a class had any overloading used to remain
360 non-overloaded even if the class gained overloading through C<use overload>
361 or @ISA changes, and even after C<bless>. This has been fixed
366 Classes with overloading can now inherit fallback values.
370 Overloading was not respecting a fallback value of 0 if there were
371 overloaded objects on both sides of an assignment operator like C<+=>
376 C<pos> now croaks with hash and array arguments, instead of producing
381 C<while(each %h)> now implies C<while(defined($_ = each %h))>, like
382 C<readline> and C<readdir>.
386 Subs in the CORE:: namespace no longer crash after C<undef *_> when called
387 with no argument list (C<&CORE::time> with no parentheses).
391 Unicode 6.1 published an incorrect alias for one of the
392 Canonical_Combining_Class property's values (which range between 0 and
393 254). The alias C<CCC133> should have been C<CCC132>. Perl now
394 overrides the data file furnished by Unicode to give the correct value.
398 C<unpack> no longer produces the "'/' must follow a numeric type in unpack"
399 error when it is the data that are at fault [perl #60204].
403 C<join> and C<"@array"> now call FETCH only once on a tied C<$">
408 Some subroutine calls generated by compiling core ops affected by a
409 C<CORE::GLOBAL> override had op checking performed twice. The checking
410 is always idempotent for pure Perl code, but the double checking can
411 matter when custom call checkers are involved.
415 A race condition used to exist around fork that could cause a signal sent to
416 the parent to be handled by both parent and child. Signals are now blocked
417 briefly around fork to prevent this from happening [perl #82580].
421 =head1 Acknowledgements
423 Perl 5.17.0 represents approximately 1 week of development since Perl 5.16.0
424 and contains approximately 17,000 lines of changes across 180 files from 26
427 Perl continues to flourish into its third decade thanks to a vibrant community
428 of users and developers. The following people are known to have contributed the
429 improvements that became Perl 5.16.1:
431 Alan Haggai Alavi, Aristotle Pagaltzis, Brian Fraser, Chris 'BinGOs' Williams,
432 Craig A. Berry, Dagfinn Ilmari Mannsåker, Eric Brine, Father Chrysostomos,
433 Igor Zaytsev, James E Keenan, Karl Williamson, Leon Timmermans, Lukas Mai,
434 Marcus Holland-Moritz, Matthew Horsfall, Moritz Lenz, Rafael Garcia-Suarez,
435 Reini Urban, Ricardo Signes, Robin Barker, Ronald J. Kimball, Smylers, Steffen
436 Müller, Steve Hay, Tony Cook, Zefram.
438 The list above is almost certainly incomplete as it is automatically generated
439 from version control history. In particular, it does not include the names of
440 the (very much appreciated) contributors who reported issues to the Perl bug
443 Many of the changes included in this version originated in the CPAN modules
444 included in Perl's core. We're grateful to the entire CPAN community for
445 helping Perl to flourish.
447 For a more complete list of all of Perl's historical contributors, please see
448 the F<AUTHORS> file in the Perl source distribution.
450 =head1 Reporting Bugs
452 If you find what you think is a bug, you might check the articles
453 recently posted to the comp.lang.perl.misc newsgroup and the perl
454 bug database at http://rt.perl.org/perlbug/ . There may also be
455 information at http://www.perl.org/ , the Perl Home Page.
457 If you believe you have an unreported bug, please run the L<perlbug>
458 program included with your release. Be sure to trim your bug down
459 to a tiny but sufficient test case. Your bug report, along with the
460 output of C<perl -V>, will be sent off to perlbug@perl.org to be
461 analysed by the Perl porting team.
463 If the bug you are reporting has security implications, which make it
464 inappropriate to send to a publicly archived mailing list, then please send
465 it to perl5-security-report@perl.org. This points to a closed subscription
466 unarchived mailing list, which includes
467 all the core committers, who will be able
468 to help assess the impact of issues, figure out a resolution, and help
469 co-ordinate the release of patches to mitigate or fix the problem across all
470 platforms on which Perl is supported. Please only use this address for
471 security issues in the Perl core, not for modules independently
476 The F<Changes> file for an explanation of how to view exhaustive details
479 The F<INSTALL> file for how to build Perl.
481 The F<README> file for general stuff.
483 The F<Artistic> and F<Copying> files for copyright information.