3 perldelta - what is new for perl v5.9.3
7 This document describes differences between the 5.9.2 and the 5.9.3
8 development releases. See L<perl590delta>, L<perl591delta> and
9 L<perl592delta> for the differences between 5.8.0 and 5.9.2.
11 =head1 Incompatible Changes
13 =head2 Parsing of C<-f _>
15 The identifier C<_> is now forced to be a bareword after a filetest
16 operator. This solves a number of misparsing issues when a global C<_>
17 subroutine is defined.
21 C<mkdir()> without arguments now defaults to C<$_>.
23 =head2 Magic goto and eval
25 The construct C<eval { goto &foo }> is now disallowed. (Note that the
26 similar construct, but with C<eval("")> instead, was already forbidden.)
28 =head2 C<$#> has been removed
30 The deprecated C<$#> variable (output format for numbers) has been
31 removed. A new warning, C<$# is no longer supported>, has been added.
35 The C<:unique> attribute has been made a no-op, since its current
36 implementation was fundamentally flawed and not threadsafe.
38 =head2 Scoping of the C<sort> pragma
40 The C<sort> pragma is now lexically scoped. Its effect used to be global.
42 =head1 Core Enhancements
44 =head2 The C<feature> pragma
46 The C<feature> pragma is used to enable new syntax that would break Perl's
47 backwards-compatibility with older releases of the language. It's a lexical
48 pragma, like C<strict> or C<warnings>.
50 Currently the following new features are available: C<switch> (adds a
51 switch statement), C<~~> (adds a Perl 6-like smart match operator), C<say>
52 (adds a C<say> built-in function), and C<err> (adds an C<err> keyword).
53 Those features are described below.
55 Note that C<err> low-precedence defined-or operator used to be enabled by
56 default (although as a weak keyword, meaning that any function would
57 override it). It's now only recognized when explicitly turned on (and is
58 then a regular keyword).
60 Those features, and the C<feature> pragma itself, have been contributed by
63 =head2 Switch and Smart Match operator
65 Perl 5 now has a switch statement. It's available when C<use feature
66 'switch'> is in effect. This feature introduces three new keywords,
67 C<given>, C<when>, and C<default>:
70 when (/^abc/) { $abc = 1; }
71 when (/^def/) { $def = 1; }
72 when (/^xyz/) { $xyz = 1; }
73 default { $nothing = 1; }
76 A more complete description of how Perl matches the switch variable
77 against the C<when> conditions is given in L<perlsyn/"Switch statements">.
79 This kind of match is called I<smart match>, and it's also possible to use
80 it outside of switch statements, via the new C<~~> operator (enabled via
81 the C<use feature '~~'> directive). See L<perlsyn/"Smart matching in
86 say() is a new built-in, only available when C<use feature 'say'> is in
87 effect, that is similar to print(), but that implicitly appends a newline
88 to the printed string. See L<perlfunc/say>.
90 =head2 C<CLONE_SKIP()>
92 Perl has now support for the C<CLONE_SKIP> special subroutine. Like
93 C<CLONE>, C<CLONE_SKIP> is called once per package; however, it is called
94 just before cloning starts, and in the context of the parent thread. If it
95 returns a true value, then no objects of that class will be cloned. See
96 L<perlmod> for details. (Contributed by Dave Mitchell.)
98 =head2 C<${^CHILD_ERROR_NATIVE}>
100 A new internal variable, C<${^CHILD_ERROR_NATIVE}>, gives the native
101 status returned by the last pipe close, backtick command, successful call
102 to wait() or waitpid(), or from the system() operator. See L<perlrun> for
103 details. (Contributed by Gisle Aas.)
107 The support for assertions, introduced in perl 5.9.0, has been improved.
108 The syntax for the C<-A> command-line switch has changed; it now accepts
109 an optional module name, defaulting to C<assertions::activate>. See
110 L<assertions> and L<perlrun>. (Contributed by Salvador Fandiño García.)
112 =head2 Unicode Character Database 4.1.0
114 The copy of the Unicode Character Database included in Perl 5.9 has
115 been updated to 4.1.0.
119 You can now use C<no> followed by a version number to specify that you
120 want to use a version of perl inferior to the specified one.
122 =head2 Recursive sort subs
124 You can now use recursive subroutines with sort(), thanks to Robin Houston.
126 =head2 Effect of pragmas in eval
128 The compile-time value of the C<%^H> hint variable can now propagate into
129 eval("")uated code. This makes it more useful to implement lexical
132 As a side-effect of this, the overloaded-ness of constants now propagates
135 =head2 New B<-E> command-line switch
137 B<-E> is equivalent to B<-e>, but it implicitly enables all
138 optional features (like C<use feature ":5.10">).
140 =head2 C<chdir>, C<chmod> and C<chown> on filehandles
142 C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
143 filenames, if the system supports respectively C<fchdir>, C<fchmod> and
144 C<fchown>, thanks to a patch provided by Gisle Aas.
148 C<$(> and C<$)> now return groups in the order where the OS returns them,
149 thanks to Gisle Aas. This wasn't previously the case.
151 =head1 Modules and Pragmata
153 =head2 New Core Modules
159 A new pragma, C<feature>, has been added; see above in L</"Core
164 C<assertions::compat>, also available on CPAN, allows the use of assertions on
165 perl versions prior to 5.9.0 (that is the first one to natively support
170 C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
171 C<Math::BigInt::Calc>.
175 C<Compress::Zlib> is an interface to the zlib compression library. It
176 comes with a bundled version of zlib, so having a working zlib is not a
177 prerequisite to install it. It's used by C<Archive::Tar> (see below).
181 C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
185 C<Archive::Tar> is a module to manipulate C<tar> archives.
189 C<Digest::SHA> is a module used to calculate many types of SHA digests,
190 has been included for SHA support in the CPAN module.
194 =head1 Utility Changes
198 C<ptar> is a pure perl implementation of C<tar>, that comes with
203 This command-line utility, used to print or to check SHA digests, comes
204 with the new C<Digest::SHA> module.
206 =head2 C<h2xs> enhancements
208 C<h2xs> implements a new option C<--use-xsloader> to force use of
209 C<XSLoader> even in backwards compatible modules.
211 The handling of authors' names that had apostrophes has been fixed.
213 Any enums with negative values are now skipped.
215 =head2 C<perlivp> enhancements
217 C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
218 option to run I<all> tests.
224 The L<perlglossary> manpage is a glossary of terms used in the Perl
225 documentation, technical and otherwise, kindly provided by O'Reilly Media,
228 L<perltodo> now lists a rough roadmap to Perl 5.10.
230 =head1 Performance Enhancements
232 =head2 XS-assisted SWASHGET
234 Some pure-perl code that perl was using to retrieve Unicode properties and
235 transliteration mappings has been reimplemented in XS.
237 =head2 Constant subroutines
239 The interpreter internals now support a far more memory efficient form of
240 inlineable constants. Storing a reference to a constant value in a symbol
241 table is equivalent to a full typeglob referencing a constant subroutine,
242 but using about 400 bytes less memory. This proxy constant subroutine is
243 automatically upgraded to a real typeglob with subroutine if necessary.
244 The approach taken is analogous to the existing space optimisation for
245 subroutine stub declarations, which are stored as plain scalars in place
246 of the full typeglob.
248 Several of the core modules have been converted to use this feature for
249 their system dependent constants - as a result C<use POSIX;> now takes about
252 =head2 C<PERL_DONT_CREATE_GVSV>
254 The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
255 in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
256 from creating an empty scalar with every new typeglob. See L<perl588delta>
259 =head2 Weak references are cheaper
261 Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
262 Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
263 happens at program exit, it may be skipped completely.
265 =head2 sort() enhancements
267 Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
268 and to speed up some cases.
270 =head1 Installation and Configuration Improvements
272 =head2 Compilation improvements
274 Parallel makes should work properly now, although there may still be problems
275 if C<make test> is instructed to run in parallel.
277 Building with Borland's compilers on Win32 should work more smoothly. In
278 particular Steve Hay has worked to side step many warnings emitted by their
279 compilers and at least one C compiler internal error.
281 Perl extensions on Windows now can be statically built into the Perl DLL,
282 thanks to a work by Vadim Konovalov.
284 =head2 New Or Improved Platforms
286 Perl is being ported to Symbian OS. See L<perlsymbian> for more
289 The VMS port has been improved. See L<perlvms>.
291 DynaLoader::dl_unload_file() now works on Windows.
293 Portability of Perl on various recent compilers on Windows has been
294 improved (Borland C++, Visual C++ 7.0).
298 C<Configure> will now detect C<clearenv> and C<unsetenv>, thanks to a
299 patch from Alan Burlison. It will also probe for C<futimes> (and use it
300 internally if available), and whether C<sprintf> correctly returns the
301 length of the formatted string.
303 =head2 Module auxiliary files
305 README files and changelogs for CPAN modules bundled with perl are no
308 =head1 Selected Bug Fixes
310 =head2 C<defined $$x>
312 C<use strict "refs"> was ignoring taking a hard reference in an argument
313 to defined(), as in :
317 if (defined $$x) {...}
319 This now correctly produces the run-time error C<Can't use string as a
320 SCALAR ref while "strict refs" in use>. (However, C<defined @$foo> and
321 C<defined %$foo> are still allowed. Those constructs are discouraged
324 =head2 Calling CORE::require()
326 CORE::require() and CORE::do() were always parsed as require() and do()
327 when they were overridden. This is now fixed.
329 =head2 Subscripts of slices
331 You can now use a non-arrowed form for chained subscripts after a list
334 ({foo => "bar"})[0]{foo}
336 This used to be a syntax error; a C<< -> >> was required.
338 =head2 Remove over-optimisation
340 Perl 5.9.2 introduced a change so that assignments of C<undef> to a
341 scalar, or of an empty list to an array or a hash, were optimised out. As
342 this could cause problems when C<goto> jumps were involved, this change
345 =head2 sprintf() fixes
347 Using the sprintf() function with some formats could lead to a buffer
348 overflow in some specific cases. This has been fixed, along with several
349 other bugs, notably in bounds checking.
351 In related fixes, it was possible for badly written code that did not follow
352 the documentation of C<Sys::Syslog> to have formatting vulnerabilities.
353 C<Sys::Syslog> has been changed to protect people from poor quality third
356 =head2 no warnings 'category' works correctly with -w
358 Previously when running with warnings enabled globally via C<-w>, selective
359 disabling of specific warning categories would actually turn off all warnings.
360 This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
361 C<io> class. Previously it would erroneously turn off all warnings.
369 C<FindBin> now works better with directories where access rights are more
370 restrictive than usual.
374 Several memory leaks in ithreads were closed. Also, ithreads were made
375 less memory-intensive.
379 Trailing spaces are now trimmed from C<$!> and C<$^E>.
383 Operations that require perl to read a process' list of groups, such as reads
384 of C<$(> and C<$)>, now dynamically allocate memory rather than using a
385 fixed sized array. The fixed size array could cause C stack exhaustion on
386 systems configured to use large numbers of groups.
390 C<PerlIO::scalar> now works better with non-default C<$/> settings.
394 The C<x> repetition operator is now able to operate on C<qw//> lists. This
395 used to raise a syntax error.
399 The debugger now traces correctly execution in eval("")uated code that
400 contains #line directives.
404 The value of the C<open> pragma is no longer ignored for three-argument
409 Perl will now use the C library calls C<unsetenv> and C<clearenv> if present
410 to delete keys from C<%ENV> and delete C<%ENV> entirely, thanks to a patch
415 =head2 More Unicode Fixes
421 chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
422 character, unless when the C<bytes> pragma is in effect, where the low
423 eight bytes of the value are used.
427 Some case insensitive matches between UTF-8 encoded data and 8 bit regexps,
428 and vice versa, could give malformed character warnings. These have been
429 fixed by Dave Mitchell and Yves Orton.
433 C<lcfirst> and C<ucfirst> could corrupt the string for certain cases where
434 the length UTF-8 encoding of the string in lower case, upper case or title
435 case differed. This was fixed by Nicholas Clark.
439 =head1 New or Changed Diagnostics
441 =head2 Attempt to set length of freed array
443 This is a new warning, produced in situations like the following one:
445 $r = do {my @a; \$#a};
448 =head2 Non-string passed as bitmask
450 This is a new warning, produced when number has been passed as a argument to
451 select(), instead of a bitmask.
453 # Wrong, will now warn
454 $rin = fileno(STDIN);
455 ($nfound,$timeleft) = select($rout=$rin, undef, undef, $timeout);
459 vec($rin,fileno(STDIN),1) = 1;
460 ($nfound,$timeleft) = select($rout=$rin, undef, undef, $timeout);
462 =head2 Search pattern not terminated or ternary operator parsed as search pattern
464 This syntax error indicates that the lexer couldn't find the final
465 delimiter of a C<?PATTERN?> construct. Mentioning the ternary operator in
466 this error message makes syntax diagnostic easier.
468 =head2 "%s" variable %s masks earlier declaration
470 This warning is now emitted in more consistent cases; in short, when one
471 of the declarations involved is a C<my> variable:
473 my $x; my $x; # warns
474 my $x; our $x; # warns
475 our $x; my $x; # warns
477 On the other hand, the following:
481 now gives a C<"our" variable %s redeclared> warning.
483 =head2 readdir()/closedir()/etc. attempted on invalid dirhandle
485 These new warnings are now emitted when a dirhandle is used but is
486 either closed or not really a dirhandle.
488 =head1 Changed Internals
490 In general, the source code of perl has been refactored, tied up, and
491 optimized in many places. Also, memory management and allocation has been
492 improved in a couple of points.
494 Andy Lester supplied many improvements to determine which function
495 parameters and local variables could actually be declared C<const> to the C
496 compiler. Steve Peters provided new C<*_set> macros and reworked the core to
497 use these rather than assigning to macros in LVALUE context.
499 Dave Mitchell improved the lexer debugging output under C<-DT>.
501 A new file, F<mathoms.c>, has been added. It contains functions that are
502 no longer used in the perl core, but that remain available for binary or
503 source compatibility reasons. However, those functions will not be
504 compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
506 The C<AvFLAGS> macro has been removed.
508 The C<av_*()> functions, used to manipulate arrays, no longer accept null
511 =head2 B:: modules inheritance changed
513 The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
514 inherits from C<B::SV> (it used to inherit from C<B::IV>).
516 =head1 Reporting Bugs
518 If you find what you think is a bug, you might check the articles
519 recently posted to the comp.lang.perl.misc newsgroup and the perl
520 bug database at http://bugs.perl.org/ . There may also be
521 information at http://www.perl.org/ , the Perl Home Page.
523 If you believe you have an unreported bug, please run the B<perlbug>
524 program included with your release. Be sure to trim your bug down
525 to a tiny but sufficient test case. Your bug report, along with the
526 output of C<perl -V>, will be sent off to perlbug@perl.org to be
527 analysed by the Perl porting team.
531 The F<Changes> file for exhaustive details on what changed.
533 The F<INSTALL> file for how to build Perl.
535 The F<README> file for general stuff.
537 The F<Artistic> and F<Copying> files for copyright information.