5 perl5216delta - what is new for perl v5.21.6
9 This document describes differences between the 5.21.5 release and the 5.21.6
12 If you are upgrading from an earlier release such as 5.21.4, first read
13 L<perl5215delta>, which describes differences between 5.21.4 and 5.21.5.
15 =head1 Core Enhancements
17 =head2 List form of pipe open implemented for Win32
19 The list form of pipe:
21 open my $fh, "-|", "program", @arguments;
23 is now implemented on Win32. It has the same limitations as C<system
24 LIST> on Win32, since the Win32 API doesn't accept program arguments
27 =head2 Assignment to list repetition
29 C<(...) x ...> can now be used within a list that is assigned to, as long
30 as the left-hand side is a valid lvalue. This allows C<(undef,undef,$foo)
31 = that_function()> to be written as C<((undef)x2, $foo) = that_function()>.
33 =head2 C<close> now sets C<$!>
35 When an I/O error occurs, the fact that there has been an error is recorded
36 in the handle. C<close> returns false for such a handle. Previously, the
37 value of C<$!> would be untouched by C<close>, so the common convention of
38 writing C<close $fh or die $!> did not work reliably. Now the handle
39 records the value of C<$!>, too, and C<close> restores it.
43 =head2 Use of non-graphic characters in single-character variable names
45 The syntax for single-character variable names is more lenient than
46 for longer variable names, allowing the one-character name to be a
47 punctuation character or even invisible (a non-graphic). Perl v5.20
48 deprecated the ASCII-range controls as such a name. Now, all
49 non-graphic characters that formerly were allowed are deprecated.
50 The practical effect of this occurs only when not under C<S<"use
51 utf8">>, and affects just the C1 controls (code points 0x80 through
52 0xFF), NO-BREAK SPACE, and SOFT HYPHEN.
54 =head2 Inlining of C<sub () { $var }> with observable side-effects
56 In many cases Perl makes sub () { $var } into an inlinable constant
57 subroutine, capturing the value of $var at the time the C<sub> expression
58 is evaluated. This can break the closure behaviour in those cases where
59 $var is subsequently modified. The subroutine won't return the new value.
61 This usage is now deprecated in those cases where the variable could be
62 modified elsewhere. Perl detects those cases and emits a deprecation
63 warning. Such code will likely change in the future and stop producing a
66 If your variable is only modified in the place where it is declared, then
67 Perl will continue to make the sub inlinable with no warnings.
71 return sub () { $var }; # fine
74 sub make_constant_deprecated {
77 return sub () { $var }; # deprecated
80 sub make_constant_deprecated2 {
82 log_that_value($var); # could modify $var
83 return sub () { $var }; # deprecated
86 In the second example above, detecting that $var is assigned to only once
87 is too hard to detect. That it happens in a spot other than the C<my>
88 declaration is enough for Perl to find it suspicious.
90 This deprecation warning happens only for a simple variable for the body of
91 the sub. (A C<BEGIN> block or C<use> statement inside the sub is ignored,
92 because it does not become part of the sub's body.) For more complex
93 cases, such as C<sub () { do_something() if 0; $var }> the behaviour has
94 changed such that inlining does not happen if the variable is modifiable
95 elsewhere. Such cases should be rare.
97 =head1 Performance Enhancements
103 C<(...)x1>, C<("constant")x0> and C<($scalar)x0> are now optimised in list
104 context. If the right-hand argument is a constant 1, the repetition
105 operator disappears. If the right-hand argument is a constant 0, the whole
106 expressions is optimised to the empty list, so long as the left-hand
107 argument is a simple scalar or constant. C<(foo())x0> is not optimised.
111 C<substr> assignment is now optimised into 4-argument C<substr> at the end
112 of a subroutine (or as the argument to C<return>). Previously, this
113 optimisation only happened in void context.
117 Assignment to lexical variables is often optimised away. For instance, in
118 C<$lexical = chr $foo>, the C<chr> operator writes directly to the lexical
119 variable instead of returning a value that gets copied. This optimisation
120 has been extended to C<split>, C<x> and C<vec> on the right-hand side. It
121 has also been made to work with state variable initialization.
125 In "\L...", "\Q...", etc., the extra "stringify" op is now optimised away,
126 making these just as fast as C<lcfirst>, C<quotemeta>, etc.
130 Assignment to an empty list is now sometimes faster. In particular, it
131 never calls C<FETCH> on tied arguments on the right-hand side, whereas it
136 =head1 Modules and Pragmata
138 =head2 Updated Modules and Pragmata
144 L<B> has been upgraded from version 1.52 to 1.53.
148 L<B::Concise> has been upgraded from version 0.994 to 0.995.
152 L<B::Deparse> has been upgraded from version 1.29 to 1.30.
154 It now deparses C<+sub : attr { ... }> correctly at the start of a
155 statement. Without the initial C<+>, C<sub> would be a statement label.
157 C<BEGIN> blocks are now emitted in the right place most of the time, but
158 the change unfortunately introduced a regression, in that C<BEGIN> blocks
159 occurring just before the end of the enclosing block may appear below it
160 instead. So this change may need to be reverted if it cannot be fixed
161 before Perl 5.22. [perl #77452]
163 B::Deparse no longer puts erroneous C<local> here and there, such as for
164 C<LIST = tr/a//d>. [perl #119815]
166 Adjacent C<use> statements are no longer accidentally nested if one
167 contains a C<do> block. [perl #115066]
171 L<B::Op_private> has been upgraded from version 5.021005 to 5.021006.
173 It now includes a hash named C<%ops_using>, list all op types that use a
174 particular private flag.
178 L<CPAN::Meta> has been upgraded from version 2.142690 to 2.143240.
182 L<CPAN::Meta::Requirements> has been upgraded from version 2.128 to 2.130.
186 L<Devel::Peek> has been upgraded from version 1.18 to 1.19.
190 L<Digest::SHA> has been upgraded from version 5.92 to 5.93.
194 L<DynaLoader> has been upgraded from version 1.27 to 1.28.
198 L<Encode> has been upgraded from version 2.62 to 2.64.
202 L<experimental> has been upgraded from version 0.012 to 0.013.
206 L<Exporter> has been upgraded from version 5.71 to 5.72.
210 L<ExtUtils::MakeMaker> has been upgraded from version 6.98 to 7.02.
214 L<ExtUtils::Manifest> has been upgraded from version 1.68 to 1.69.
218 L<ExtUtils::ParseXS> has been upgraded from version 3.25 to 3.26.
222 L<HTTP::Tiny> has been upgraded from version 0.050 to 0.051.
226 L<I18N::Langinfo> has been upgraded from version 0.11 to 0.12.
230 L<IO::Socket> has been upgraded from version 1.37 to 1.38.
232 Document the limitations of the isconnected() method. [perl #123096]
236 L<locale> has been upgraded from version 1.04 to 1.05.
240 L<Module::CoreList> has been upgraded from version 5.20141020 to 5.20141120.
244 L<overload> has been upgraded from version 1.23 to 1.24.
248 L<PerlIO::encoding> has been upgraded from version 0.19 to 0.20.
252 L<PerlIO::scalar> has been upgraded from version 0.19 to 0.20.
256 L<POSIX> has been upgraded from version 1.45 to 1.46.
260 L<re> has been upgraded from version 0.27 to 0.28.
264 L<Test::Harness> has been upgraded from version 3.33 to 3.34.
268 L<Test::Simple> has been upgraded from version 1.001008 to 1.301001_075.
272 L<Unicode::UCD> has been upgraded from version 0.58 to 0.59.
276 L<warnings> has been upgraded from version 1.28 to 1.29.
280 L<XSLoader> has been upgraded from version 0.18 to 0.19.
286 =head2 Changes to Existing Documentation
288 =head3 L<perldata/Identifier parsing>
294 The syntax of single-character variable names has been brought
295 up-to-date and more fully explained.
301 The following additions or changes have been made to diagnostic output,
302 including warnings and fatal error messages. For the complete list of
303 diagnostic messages, see L<perldiag>.
305 =head2 New Diagnostics
313 L<Use of literal non-graphic characters in variable names is deprecated|perldiag/"Use of literal non-graphic characters in variable names is deprecated">
317 A new C<locale> warning category has been created, with the following warning
318 messages currently in it:
324 L<Locale '%s' may not work well.%s|perldiag/Locale '%s' may not work well.%s>
328 L<Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".|perldiag/Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".>
334 L<Warning: unable to close filehandle %s properly: %s|perldiag/"Warning: unable to close filehandle %s properly: %s">
338 The following two warnings for C<tr///> used to be skipped if the
339 transliteration contained wide characters, but now they occur regardless of
340 whether there are wide characters or not:
342 L<Useless use of E<sol>d modifier in transliteration operator|perldiag/"Useless use of /d modifier in transliteration operator">
344 L<Replacement list is longer than search list|perldiag/Replacement list is longer than search list>
348 =head2 Changes to Existing Diagnostics
354 L<Quantifier unexpected on zero-length expression in regex mE<sol>%sE<sol>|perldiag/"Quantifier unexpected on zero-length expression in regex m/%s/">.
356 This message has had the S<"<-- HERE"> marker removed, as it was always
357 placed at the end of the regular expression, regardless of where the
358 problem actually occurred. [perl #122680]
362 L<Setting $E<sol> to a reference to %s as a form of slurp is deprecated, treating as undef|perldiag/"Setting $/ to a reference to %s as a form of slurp is deprecated, treating as undef">
364 This warning is now a default warning, like other deprecation warnings.
368 =head1 Configuration and Compilation
374 F<Configure> with C<-Dmksymlinks> should now be faster. [perl #122002]
382 As well as the gzip and bzip2 tarballs, this release has been made available as an xz utils compressed tarball.
386 =head1 Platform Support
388 =head2 Platform-Specific Notes
396 In the experimental C<:win32> layer, a crash in C<open> was fixed. Also
397 opening C</dev/null>, which works the Win32 Perl's normal C<:unix> layer, was
398 implemented for C<:win32>.
399 L<[perl #122224]|https://rt.perl.org/Ticket/Display.html?id=122224>
403 A new makefile option, C<USE_LONG_DOUBLE>, has been added to the Windows
404 dmake makefile for gcc builds only. Set this to "define" if you want perl to
405 use long doubles to give more accuracy and range for floating point numbers.
409 =head1 Internal Changes
415 C<screaminstr> has been removed. Although marked as public API, it is
416 undocumented and has no usage in modern perl versions on CPAN Grep. Calling it
417 has been fatal since 5.17.0.
421 C<newDEFSVOP>, C<block_start>, C<block_end> and C<intro_my> have been added
426 The internal C<convert> function in F<op.c> has been renamed
427 C<op_convert_list> and added to the API.
431 C<sv_magic> no longer forbids "ext" magic on read-only values. After all,
432 perl can't know whether the custom magic will modify the SV or not.
437 Starting in 5.21.6, accessing L<perlapi/CvPADLIST> in an XSUB is forbidden.
438 CvPADLIST has be reused for a different internal purpose for XSUBs. Guard all
439 CvPADLIST expressions with C<CvISXSUB()> if your code doesn't already block
440 XSUB CV*s from going through optree CV* expecting code.
445 =head1 Selected Bug Fixes
451 fchmod() and futimes() now set C<$!> when they fail due to being
452 passed a closed file handle. [perl #122703]
456 Perl now comes with a corrected Unicode 7.0 for the erratum issued on
457 October 21, 2014 (see L<http://www.unicode.org/errata/#current_errata>),
458 dealing with glyph shaping in Arabic.
462 op_free() no longer crashes due to a stack overflow when freeing a
463 deeply recursive op tree. [perl #108276]
467 scalarvoid() would crash due to a stack overflow when processing a
468 deeply recursive op tree. [perl #108276]
472 In Perl 5.20.0, C<$^N> accidentally had the internal UTF8 flag turned off
473 if accessed from a code block within a regular expression, effectively
474 UTF8-encoding the value. This has been fixed. [perl #123135]
478 A failed C<semctl> call no longer overwrites existing items on the stack,
479 causing C<(semctl(-1,0,0,0))[0]> to give an "uninitialized" warning.
483 C<else{foo()}> with no space before C<foo> is now better at assigning the
484 right line number to that statement. [perl #122695]
488 Sometimes the assignment in C<@array = split> gets optimised and C<split>
489 itself writes directly to the array. This caused a bug, preventing this
490 assignment from being used in lvalue context. So
491 C<(@a=split//,"foo")=bar()> was an error. (This bug probably goes back to
492 Perl 3, when the optimisation was added.) This optimisation, and the bug,
493 started to happen in more cases in 5.21.5. It has now been fixed.
498 When argument lists that fail the checks installed by subroutine
499 signatures, the resulting error messages now give the file and line number
500 of the caller, not of the called subroutine. [perl #121374]
504 Flip-flop operators (C<..> and C<...> in scalar context) used to maintain
505 a separate state for each recursion level (the number of times the
506 enclosing sub was called recursively), contrary to the documentation. Now
507 each closure has one internal state for each flip-flop. [perl #122829]
511 C<use>, C<no>, statement labels, special blocks (C<BEGIN>) and pod are now
512 permitted as the first thing in a C<map> or C<grep> block, the block after
513 C<print> or C<say> (or other functions) returning a handle, and within
514 C<${...}>, C<@{...}>, etc. [perl #122782]
518 The repetition operator C<x> now propagates lvalue context to its left-hand
519 argument when used in contexts like C<foreach>. That allows
520 C<for(($#that_array)x2) { ... }> to work as expected if the loop modifies
525 C<(...) x ...> in scalar context used to corrupt the stack if one operand
526 were an object with "x" overloading, causing erratic behaviour.
531 Assignment to a lexical scalar is often optimised away (as mentioned under
532 L</Performance Enhancements>). Various bugs related to this optimisation
533 have been fixed. Certain operators on the right-hand side would sometimes
534 fail to assign the value at all or assign the wrong value, or would call
535 STORE twice or not at all on tied variables. The operators affected were
536 C<$foo++>, C<$foo-->, and C<-$foo> under C<use integer>, C<chomp>, C<chr>
541 List assignments were sometimes buggy if the same scalar ended up on both
542 sides of the assignment due to used of C<tied>, C<values> or C<each>. The
543 result would be the wrong value getting assigned.
547 C<setpgrp($nonzero)> (with one argument) was accidentally changed in 5.16
548 to mean C<setpgrp(0)>. This has been fixed.
552 C<__SUB__> could return the wrong value or even corrupt memory under the
553 debugger (the B<-d> switch) and in subs containing C<eval $string>.
557 When C<sub () { $var }> becomes inlinable, it now returns a different
558 scalar each time, just as a non-inlinable sub would, though Perl still
559 optimises the copy away in cases where it would make no observable
564 C<my sub f () { $var }> and C<sub () : attr { $var }> are no longer
565 eligible for inlining. The former would crash; the latter would just
566 throw the attributes away. An exception is made for the little-known
567 ":method" attribute, which does nothing much.
571 Inlining of subs with an empty prototype is now more consistent than
572 before. Previously, a sub with multiple statements, all but the last
573 optimised away, would be inlinable only if it were an anonymous sub
574 containing a string C<eval> or C<state> declaration or closing over an
575 outer lexical variable (or any anonymous sub under the debugger). Now any
576 sub that gets folded to a single constant after statements have been
577 optimised away is eligible for inlining. This applies to things like C<sub
578 () { jabber() if DEBUG; 42 }>.
580 Some subroutines with an explicit C<return> were being made inlinable,
581 contrary to the documentation, Now C<return> always prevents inlining.
585 On some systems, such as VMS, C<crypt> can return a non-ASCII string. If a
586 scalar assigned to had contained a UTF8 string previously, then C<crypt>
587 would not turn off the UTF8 flag, thus corrupting the return value. This
588 would happen with C<$lexical = crypt ...>.
592 C<crypt> no longer calls C<FETCH> twice on a tied first argument.
596 An unterminated here-doc on the last line of a quote-like operator
597 (C<qq[${ <<END }]>, C</(?{ <<END })/>) no longer causes a double free. It
598 started doing so in 5.18.
602 Fixed two assertion failures introduced into C<-DPERL_OP_PARENT>
603 builds. [perl #108276]
607 =head1 Known Problems
613 Builds on FreeBSD 10.x currently fail when compiling L<POSIX>. A workaround is
614 to specify C<-Ui_fenv> when running C<Configure>.
618 =head1 Errata From Previous Releases
624 Due to a mistake in the string-copying logic, copying the value of a state
625 variable could instead steal the value and undefine the variable. This
626 bug, introduced in 5.20, would happen mostly for long strings (1250 chars
627 or more), but could happen for any strings under builds with copy-on-write
628 disabled. [perl #123029]
630 This bug was actually fixed in 5.21.5, but it was not until after that
631 release that this bug, and the fact that it had been fixed, were
636 If a named sub tries to access a scalar declared in an outer anonymous sub,
637 the variable is not available, so the named sub gets its own undefined
638 scalar. In 5.10, attempts to take a reference to the variable
639 (C<\$that_variable>) began returning a reference to a I<copy> of it
640 instead. This was accidentally fixed in 5.21.4, but the bug and its fix
641 were not noticed till now.
645 =head1 Acknowledgements
647 Perl 5.21.6 represents approximately 4 weeks of development since Perl 5.21.5
648 and contains approximately 60,000 lines of changes across 920 files from 25
651 Excluding auto-generated files, documentation and release tools, there were
652 approximately 48,000 lines of changes to 630 .pm, .t, .c and .h files.
654 Perl continues to flourish into its third decade thanks to a vibrant community
655 of users and developers. The following people are known to have contributed the
656 improvements that became Perl 5.21.6:
658 Aaron Crane, Abigail, Andrew Fresh, Andy Dougherty, Brian Fraser, Chad Granum,
659 Chris 'BinGOs' Williams, Craig A. Berry, Daniel Dragan, David Mitchell, Doug
660 Bell, Father Chrysostomos, Glenn D. Golden, James E Keenan, Jarkko Hietaniemi,
661 Jim Cromie, Karen Etheridge, Karl Williamson, Lukas Mai, Ricardo Signes, Shlomi
662 Fish, Slaven Rezic, Steve Hay, Tony Cook, Yaroslav Kuzmin.
664 The list above is almost certainly incomplete as it is automatically generated
665 from version control history. In particular, it does not include the names of
666 the (very much appreciated) contributors who reported issues to the Perl bug
669 Many of the changes included in this version originated in the CPAN modules
670 included in Perl's core. We're grateful to the entire CPAN community for
671 helping Perl to flourish.
673 For a more complete list of all of Perl's historical contributors, please see
674 the F<AUTHORS> file in the Perl source distribution.
676 =head1 Reporting Bugs
678 If you find what you think is a bug, you might check the articles recently
679 posted to the comp.lang.perl.misc newsgroup and the perl bug database at
680 https://rt.perl.org/ . There may also be information at
681 http://www.perl.org/ , the Perl Home Page.
683 If you believe you have an unreported bug, please run the L<perlbug> program
684 included with your release. Be sure to trim your bug down to a tiny but
685 sufficient test case. Your bug report, along with the output of C<perl -V>,
686 will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
688 If the bug you are reporting has security implications, which make it
689 inappropriate to send to a publicly archived mailing list, then please send it
690 to perl5-security-report@perl.org. This points to a closed subscription
691 unarchived mailing list, which includes all the core committers, who will be
692 able to help assess the impact of issues, figure out a resolution, and help
693 co-ordinate the release of patches to mitigate or fix the problem across all
694 platforms on which Perl is supported. Please only use this address for
695 security issues in the Perl core, not for modules independently distributed on
700 The F<Changes> file for an explanation of how to view exhaustive details on
703 The F<INSTALL> file for how to build Perl.
705 The F<README> file for general stuff.
707 The F<Artistic> and F<Copying> files for copyright information.