5 [ this is a template for a new perldelta file. Any text flagged as XXX needs
6 to be processed before release. ]
8 perldelta - what is new for perl v5.19.1
12 This document describes differences between the 5.19.0 release and the 5.19.1
17 XXX Any important notices here
19 =head1 Core Enhancements
21 XXX New core language features go here. Summarize user-visible core language
22 enhancements. Particularly prominent performance optimisations could go
23 here, but most should go in the L</Performance Enhancements> section.
25 [ List each enhancement as a =head2 entry ]
29 XXX Any security-related notices go here. In particular, any security
30 vulnerabilities closed should be noted here rather than in the
31 L</Selected Bug Fixes> section.
33 [ List each security issue as a =head2 entry ]
35 =head1 Incompatible Changes
37 XXX For a release on a stable branch, this section aspires to be:
39 There are no changes intentionally incompatible with 5.XXX.XXX
40 If any exist, they are bugs, and we request that you submit a
41 report. See L</Reporting Bugs> below.
43 [ List each incompatible change as a =head2 entry ]
47 XXX Any deprecated features, syntax, modules etc. should be listed here.
49 =head2 Module removals
51 XXX Remove this section if inapplicable.
53 The following modules will be removed from the core distribution in a future
54 release, and will at that time need to be installed from CPAN. Distributions
55 on CPAN which require these modules will need to list them as prerequisites.
57 The core versions of these modules will now issue C<"deprecated">-category
58 warnings to alert you to this fact. To silence these deprecation warnings,
59 install the modules in question from CPAN.
61 Note that these are (with rare exceptions) fine modules that you are encouraged
62 to continue to use. Their disinclusion from core primarily hinges on their
63 necessity to bootstrapping a fully functional, CPAN-capable Perl installation,
64 not usually on concerns over their design.
66 XXX Note that deprecated modules should be listed here even if they are listed
67 as an updated module in the L</Modules and Pragmata> section.
77 [ List each other deprecation as a =head2 entry ]
79 =head1 Performance Enhancements
81 XXX Changes which enhance performance without changing behaviour go here.
82 There may well be none in a stable release.
84 [ List each enhancement as a =item entry ]
90 Perl has a new copy-on-write mechanism that avoids the need to copy the
91 internal string buffer when assigning from one scalar to another. This
92 makes copying large strings appear much faster. Modifying one of the two
93 (or more) strings after an assignment will force a copy internally. This
94 makes it unnecessary to pass strings by reference for efficiency.
96 This feature was already available in 5.18.0, but wasn't enabled by
97 default. It is the default now, and so you no longer need build perl with
98 the F<Configure> argument:
100 -Accflags=PERL_NEW_COPY_ON_WRITE
102 It can be disabled (for now) in a perl build with:
104 -Accflags=PERL_NO_COW
108 =head1 Modules and Pragmata
110 XXX All changes to installed files in F<cpan/>, F<dist/>, F<ext/> and F<lib/>
111 go here. If Module::CoreList is updated, generate an initial draft of the
112 following sections using F<Porting/corelist-perldelta.pl>, which prints stub
113 entries to STDOUT. Results can be pasted in place of the '=head2' entries
114 below. A paragraph summary for important changes should then be added by hand.
115 In an ideal world, dual-life modules would have a F<Changes> file that could be
118 [ Within each section, list entries as a =item entry ]
120 =head2 New Modules and Pragmata
130 =head2 Updated Modules and Pragmata
136 Test::Harness has been upgraded from version 3.26 to 3.28
138 Memory usage is dramatically reduced. t/harness now uses about 10% of the
139 memory used by 3.26 and earlier.
141 C<PERL5LIB> is always propagated to a test's C<@INC>, even under C<-T>.
145 Unicode::UCD has been upgraded from version 0.51 to 0.52.
147 A function, L<Unicode::UCD/search_invlist()> is now available to do
148 search an inversion list or map for a code point.
152 =head2 Removed Modules and Pragmata
164 XXX Changes to files in F<pod/> go here. Consider grouping entries by
165 file and be sure to link to the appropriate page, e.g. L<perlfunc>.
167 =head2 New Documentation
169 XXX Changes which create B<new> files in F<pod/> go here.
173 XXX Description of the purpose of the new file here
175 =head2 Changes to Existing Documentation
177 XXX Changes which significantly change existing files in F<pod/> go here.
178 However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
187 XXX Description of the change here
193 The following additions or changes have been made to diagnostic output,
194 including warnings and fatal error messages. For the complete list of
195 diagnostic messages, see L<perldiag>.
197 XXX New or changed warnings emitted by the core's C<C> code go here. Also
198 include any changes in L<perldiag> that reconcile it to the C<C> code.
200 =head2 New Diagnostics
202 XXX Newly added diagnostic messages go under here, separated into New Errors
211 XXX L<message|perldiag/"message">
221 XXX L<message|perldiag/"message">
225 =head2 Changes to Existing Diagnostics
227 XXX Changes (i.e. rewording) of diagnostic messages go here
233 XXX Describe change here
237 =head1 Utility Changes
239 XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go here.
240 Most of these are built within the directories F<utils> and F<x2p>.
242 [ List utility changes as a =head3 entry for each utility and =item
243 entries for each change
244 Use L<XXX> with program names to get proper documentation linking. ]
246 =head3 F<bisect.pl> enhancements
248 The git bisection tool F<Porting/bisect.pl> has had many enhancements.
254 Can optionally run the test case with a timeout.
258 Can now run in-place in a clean git checkout.
262 Can run the test case under C<valgrind>.
266 Can apply user supplied patches and fixes to the source checkout before
271 Now has fixups to enable building several more historical ranges of bleadperl,
272 which can be useful for pinpointing the origins of bugs or behaviour changes.
276 It is provided as part of the source distribution but not installed because
277 it is not self-contained as it relies on being run from within a git
278 checkout. Note also that it makes no attempt to fix tests, correct runtime
279 bugs or make something useful to install - its purpose is to make minimal
280 changes to get any historical revision of interest to build and run as close
281 as possible to "as-was", and thereby make C<git bisect> easy to use.
283 =head1 Configuration and Compilation
285 XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
286 go here. Any other changes to the Perl build process should be listed here.
287 However, any platform-specific changes should be listed in the
288 L</Platform Support> section, instead.
290 [ List changes as a =item entry ].
302 XXX Any significant changes to the testing of a freshly built perl should be
303 listed here. Changes which create B<new> files in F<t/> go here as do any
304 large changes to the testing harness (e.g. when parallel testing was added).
305 Changes to existing files in F<t/> aren't worth summarizing, although the bugs
306 that they represent may be covered elsewhere.
308 [ List each test improvement as a =item entry ]
318 =head1 Platform Support
320 XXX Any changes to platform support should be listed in the sections below.
322 [ Within the sections, list each platform as a =item entry with specific
323 changes as paragraphs below it. ]
327 XXX List any platforms that this version of perl compiles on, that previous
328 versions did not. These will either be enabled by new files in the F<hints/>
329 directories, or new subdirectories and F<README> files at the top level of the
334 =item XXX-some-platform
340 =head2 Discontinued Platforms
342 XXX List any platforms that this version of perl no longer compiles on.
346 =item XXX-some-platform
352 =head2 Platform-Specific Notes
354 XXX List any changes for specific platforms. This could include configuration
355 and compilation changes or changes in portability/compatibility. However,
356 changes within modules for platforms should generally be listed in the
357 L</Modules and Pragmata> section.
361 =item Mixed-endian platforms
363 The code supporting C<pack> and C<unpack> operations on mixed endian
364 platforms has been removed. We believe that Perl has long been unable to
365 build on mixed endian architectures (such as PDP-11s), so we don't think
366 that this change will affect any platforms which are able to build v5.18.0.
370 =head1 Internal Changes
372 XXX Changes which affect the interface available to C<XS> code go here. Other
373 significant internal changes for future core maintainers should be noted as
376 [ List each change as a =item entry ]
382 Perl's new copy-on-write mechanism (which is now enabled by default),
383 allows any C<SvPOK> scalar to be automatically upgraded to a copy-on-write
384 scalar when copied. A reference count on the string buffer is stored in
385 the string buffer itself.
389 $ perl -MDevel::Peek -e'$a="abc"; $b = $a; Dump $a; Dump $b'
390 SV = PV(0x260cd80) at 0x2620ad8
392 FLAGS = (POK,IsCOW,pPOK)
393 PV = 0x2619bc0 "abc"\0
397 SV = PV(0x260ce30) at 0x2620b20
399 FLAGS = (POK,IsCOW,pPOK)
400 PV = 0x2619bc0 "abc"\0
405 Note that both scalars share the same PV buffer and have a COW_REFCNT
408 This means that XS code which wishes to modify the C<SvPVX()> buffer of an
409 SV should call C<SvPV_force()> or similar first, to ensure a valid (and
410 unshared) buffer, and to call C<SvSETMAGIC()> afterwards. This in fact has
411 always been the case (for example hash keys were already copy-on-write);
412 this change just spreads the COW behaviour to a wider variety of SVs.
414 One important difference is that before 5.18.0, shared hash-key scalars
415 used to have the C<SvREADONLY> flag set; this is no longer the case.
417 This new behaviour can still be disabled by running F<Configure> with
418 B<-Accflags=-DPERL_NO_COW>. This option will probably be removed in Perl
423 C<PL_sawampersand> is now a constant. The switch this variable provided
424 (to enable/disable the pre-match copy depending on whether C<$&> had been
425 seen) has been removed and replaced with copy-on-write, eliminating a few
428 The previous behaviour can still be enabled by running F<Configure> with
429 B<-Accflags=-DPERL_SAWAMPERSAND>.
433 The functions C<my_swap>, C<my_htonl> and C<my_ntohl> have been removed.
434 It is unclear why these functions were ever marked as I<A>, part of the
435 API. XS code can't call them directly, as it can't rely on them being
436 compiled. Unsurprisingly, no code on CPAN references them.
440 =head1 Selected Bug Fixes
442 XXX Important bug fixes in the core language are summarized here. Bug fixes in
443 files in F<ext/> and F<lib/> are best summarized in L</Modules and Pragmata>.
445 [ List each fix as a =item entry ]
451 The OP allocation code now returns correctly aligned memory in all cases
452 for C<struct pmop>. Previously it could return memory only aligned to a
453 4-byte boundary, which is not correct for an ithreads build with 64 bit IVs
454 on some 32 bit platforms. Notably, this caused the build to fail completely
455 on sparc GNU/Linux. [RT #118055]
459 The debugger's C<man> command been fixed. It was broken in the v5.18.0
460 release. The C<man> command is aliased to the names C<doc> and C<perldoc> -
465 =head1 Known Problems
467 XXX Descriptions of platform agnostic bugs we know we can't fix go here. Any
468 tests that had to be C<TODO>ed for the release would be noted here. Unfixed
469 platform specific bugs also go here.
471 [ List each fix as a =item entry ]
483 XXX If any significant core contributor has died, we've added a short obituary
486 =head1 Acknowledgements
488 XXX Generate this with:
490 perl Porting/acknowledgements.pl v5.19.1..HEAD
492 =head1 Reporting Bugs
494 If you find what you think is a bug, you might check the articles recently
495 posted to the comp.lang.perl.misc newsgroup and the perl bug database at
496 http://rt.perl.org/perlbug/ . There may also be information at
497 http://www.perl.org/ , the Perl Home Page.
499 If you believe you have an unreported bug, please run the L<perlbug> program
500 included with your release. Be sure to trim your bug down to a tiny but
501 sufficient test case. Your bug report, along with the output of C<perl -V>,
502 will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
504 If the bug you are reporting has security implications, which make it
505 inappropriate to send to a publicly archived mailing list, then please send it
506 to perl5-security-report@perl.org. This points to a closed subscription
507 unarchived mailing list, which includes all the core committers, who will be
508 able to help assess the impact of issues, figure out a resolution, and help
509 co-ordinate the release of patches to mitigate or fix the problem across all
510 platforms on which Perl is supported. Please only use this address for
511 security issues in the Perl core, not for modules independently distributed on
516 The F<Changes> file for an explanation of how to view exhaustive details on
519 The F<INSTALL> file for how to build Perl.
521 The F<README> file for general stuff.
523 The F<Artistic> and F<Copying> files for copyright information.