3 perldelta - what is new for perl v5.9.5
7 This document describes differences between the 5.9.4 and the 5.9.5
8 development releases. See L<perl590delta>, L<perl591delta>,
9 L<perl592delta>, L<perl593delta> and L<perl594delta> for the differences
10 between 5.8.0 and 5.9.4.
12 =head1 Incompatible Changes
14 =head2 Tainting and printf
16 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
17 reject any tainted format argument. (Rafael Garcia-Suarez)
19 =head2 undef and signal handlers
21 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
22 equivalent to setting it to C<'DEFAULT'>. (Rafael)
24 =head2 strictures and array/hash dereferencing in defined()
26 C<defined @$foo> and C<defined %$bar> are now subject to C<strict 'refs'>
27 (that is, C<$foo> and C<$bar> shall be proper references there.)
30 (However, C<defined(@foo)> and C<defined(%bar)> are discouraged constructs
33 =head2 C<(?p{})> has been removed
35 The regular expression construct C<(?p{})>, which was deprecated in perl
36 5.8, has been removed. Use C<(??{})> instead. (Rafael)
38 =head2 Removal of the bytecode compiler and of perlcc
40 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
41 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
42 experimental tools have never worked reliably, and, due to the lack of
43 volunteers to keep them in line with the perl interpreter developments, it
44 was decided to remove them instead of shipping a broken version of those.
45 The last version of those modules can be found with perl 5.9.4.
47 However the B compiler framework stays supported in the perl core, as with
48 the more useful modules it has permitted (among others, B::Deparse and
51 =head2 Removal of the JPL
53 The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
55 =head2 Recursive inheritance detected earlier
57 Perl will now immediately throw an exception if you modify any package's
58 C<@ISA> in such a way that it would cause recursive inheritance.
60 Previously, the exception would not occur until Perl attempted to make
61 use of the recursive inheritance while resolving a method or doing a
62 C<$foo-E<gt>isa($bar)> lookup.
64 =head1 Core Enhancements
66 =head2 Regular expressions
70 =item Recursive Patterns
72 It is now possible to write recursive patterns without using the C<(??{})>
73 construct. This new way is more efficient, and in many cases easier to
76 Each capturing parenthesis can now be treated as an independent pattern
77 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
78 "parenthesis number"). For example, the following pattern will match
79 nested balanced angle brackets:
83 ( # start capture buffer 1
84 < # match an opening angle bracket
86 (?> # don't backtrack over the inside of this group
87 [^<>]+ # one or more non angle brackets
88 ) # end non backtracking group
90 (?1) # recurse to bracket 1 and try it again
92 > # match a closing angle bracket
93 ) # end capture buffer one
97 Note, users experienced with PCRE will find that the Perl implementation
98 of this feature differs from the PCRE one in that it is possible to
99 backtrack into a recursed pattern, whereas in PCRE the recursion is
100 atomic or "possessive" in nature. (Yves Orton)
102 =item Named Capture Buffers
104 It is now possible to name capturing parenthesis in a pattern and refer to
105 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
106 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
107 syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
108 access the contents of the capture buffers.
110 Thus, to replace all doubled chars, one could write
112 s/(?<letter>.)\k<letter>/$+{letter}/g
114 Only buffers with defined contents will be "visible" in the C<%+> hash, so
115 it's possible to do something like
117 foreach my $name (keys %+) {
118 print "content of buffer '$name' is $+{$name}\n";
121 The C<%-> hash is a bit more complete, since it will contain array refs
122 holding values from all capture buffers similarly named, if there should
125 C<%+> and C<%-> are implemented as tied hashes through the new module
126 C<Tie::Hash::NamedCapture>.
128 Users exposed to the .NET regex engine will find that the perl
129 implementation differs in that the numerical ordering of the buffers
130 is sequential, and not "unnamed first, then named". Thus in the pattern
132 /(A)(?<B>B)(C)(?<D>D)/
134 $1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
135 $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
136 would expect. This is considered a feature. :-) (Yves Orton)
138 =item Possessive Quantifiers
140 Perl now supports the "possessive quantifier" syntax of the "atomic match"
141 pattern. Basically a possessive quantifier matches as much as it can and never
142 gives any back. Thus it can be used to control backtracking. The syntax is
143 similar to non-greedy matching, except instead of using a '?' as the modifier
144 the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
145 quantifiers. (Yves Orton)
147 =item Backtracking control verbs
149 The regex engine now supports a number of special-purpose backtrack
150 control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
151 and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
153 =item Relative backreferences
155 A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
156 safer form of back-reference notation as well as allowing relative
157 backreferences. This should make it easier to generate and embed patterns
158 that contain backreferences. See L<perlre/"Capture buffers">. (Yves Orton)
162 The functionality of Jeff Pinyan's module Regexp::Keep has been added to
163 the core. You can now use in regular expressions the special escape C<\K>
164 as a way to do something like floating length positive lookbehind. It is
165 also useful in substitutions like:
169 that can now be converted to
173 which is much more efficient. (Yves Orton)
175 =item Vertical and horizontal whitespace, and linebreak
177 Regular expressions now recognize the C<\v> and C<\h> escapes, that match
178 vertical and horizontal whitespace, respectively. C<\V> and C<\H>
179 logically match their complements.
181 C<\R> matches a generic linebreak, that is, vertical whitespace, plus
182 the multi-character sequence C<"\x0D\x0A">.
186 =head2 The C<_> prototype
188 A new prototype character has been added. C<_> is equivalent to C<$> (it
189 denotes a scalar), but defaults to C<$_> if the corresponding argument
190 isn't supplied. Due to the optional nature of the argument, you can only
191 use it at the end of a prototype, or before a semicolon.
193 This has a small incompatible consequence: the prototype() function has
194 been adjusted to return C<_> for some built-ins in appropriate cases (for
195 example, C<prototype('CORE::rmdir')>). (Rafael)
197 =head2 UNITCHECK blocks
199 C<UNITCHECK>, a new special code block has been introduced, in addition to
200 C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
202 C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
203 are always executed at the transition between the compilation and the
204 execution of the main program, and thus are useless whenever code is
205 loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
206 just after the unit which defined them has been compiled. See L<perlmod>
207 for more information. (Alex Gough)
209 =head2 readpipe() is now overridable
211 The built-in function readpipe() is now overridable. Overriding it permits
212 also to override its operator counterpart, C<qx//> (a.k.a. C<``>).
213 Moreover, it now defaults to C<$_> if no argument is provided. (Rafael)
215 =head2 default argument for readline()
217 readline() now defaults to C<*ARGV> if no argument is provided. (Rafael)
221 The copy of the Unicode Character Database included in Perl 5.9 has
222 been updated to version 5.0.0.
226 The smart match operator (C<~~>) is now available by default (you don't
227 need to enable it with C<use feature> any longer). (Michael G Schwern)
229 =head2 Implicit loading of C<feature>
231 The C<feature> pragma is now implicitly loaded when you require a minimal
232 perl version (with the C<use VERSION> construct) greater than, or equal
235 =head1 Modules and Pragmas
237 =head2 New Pragma, C<mro>
239 A new pragma, C<mro> (for Method Resolution Order) has been added. It
240 permits to switch, on a per-class basis, the algorithm that perl uses to
241 find inherited methods in case of a mutiple inheritance hierachy. The
242 default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
243 available: the C3 algorithm. See L<mro> for more information.
246 =head2 bignum, bigint, bigrat
248 The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
249 lexically scoped. (Tels)
251 =head2 New Core Modules
257 C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
258 C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
259 included in the perl core; the behaviour of C<Locale::Maketext::Simple>
260 gracefully degrades when the later isn't present.
264 C<Params::Check> implements a generic input parsing/checking mechanism. It
269 C<Term::UI> simplifies the task to ask questions at a terminal prompt.
273 C<Object::Accessor> provides an interface to create per-object accessors.
277 C<Module::Pluggable> is a simple framework to create modules that accept
278 pluggable sub-modules.
282 C<Module::Load::Conditional> provides simple ways to query and possibly
283 load installed modules.
287 C<Time::Piece> provides an object oriented interface to time functions,
288 overriding the built-ins localtime() and gmtime().
292 C<IPC::Cmd> helps to find and run external commands, possibly
297 C<File::Fetch> provide a simple generic file fetching mechanism.
301 C<Archive::Extract> is a generic archive extraction mechanism
302 for F<.tar> (plain, gziped or bzipped) or F<.zip> files.
306 C<CPANPLUS> provides an API and a command-line tool to access the CPAN
311 =head2 Module changes
317 The C<base> pragma now warns if a class tries to inherit from itself.
320 =item C<strict> and C<warnings>
322 C<strict> and C<warnings> will now complain loudly if they are loaded via
323 incorrect casing (as in C<use Strict;>). (Johan Vromans)
327 The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
328 that used C<Carp> routines without having loaded it at compile time might
329 need to be adjusted; typically, the following (faulty) code won't work
330 anymore, and will require parentheses to be added after the function name:
334 Carp::confess "argh";
338 C<less> now does something useful (or at least it tries to). In fact, it
339 has been turned into a lexical pragma. So, in your modules, you can now
340 test whether your users have requested to use less CPU, or less memory,
341 less magic, or maybe even less fat. See L<less> for more. (Joshua ben
344 =item C<Attribute::Handlers>
346 C<Attribute::Handlers> can now report the caller's file and line number.
351 C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
352 with plugins. (Joshua ben Jore)
356 It's now possible to access the lexical pragma hints (C<%^H>) by using the
357 method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
358 can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
361 =for p5p XXX document this in B.pm too
365 As the old 5005thread threading model has been removed, in favor of the
366 ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
367 be used in old code only.
371 =head1 Utility Changes
375 C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, an
376 helper for CPANPLUS operation, has been added too, but isn't intended for
381 C<cpan2dist> is a new utility, that comes with CPANPLUS. It's a tool to
382 create distributions (or packages) from CPAN modules.
386 The output of C<pod2html> has been enhanced to be more customizable via
387 CSS. Some formatting problems were also corrected. (Jari Aalto)
391 =head2 New manpage, perlunifaq
393 A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
396 =head1 Performance Enhancements
398 =head1 Installation and Configuration Improvements
400 =head2 C++ compatibility
402 Efforts have been made to make perl and the core XS modules compilable
403 with various C++ compilers (although the situation is not perfect with
404 some of the compilers on some of the platforms tested.)
408 Perl now can be compiled with Microsoft Visual C++ 2005.
410 =head2 Static build on Win32
412 It's now possible to build a C<perl-static.exe> that doesn't depend
413 on C<perl59.dll> on Win32. See the Win32 makefiles for details.
416 =head2 C<d_pseudofork>
418 A new configuration variable, available as C<$Config{d_pseudofork}> in
419 the L<Config> module, has been added, to distinguish real fork() support
420 from fake pseudofork used on Windows platforms.
424 Perl has been reported to work on MidnightBSD.
426 =head1 Selected Bug Fixes
428 PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
429 seek() is now supported with PerlIO::scalar-based filehandles, the
430 underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
432 study() never worked for UTF-8 strings, but could lead to false results.
433 It's now a no-op on UTF-8 data. (Yves Orton)
435 The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
436 "unsafe" manner (contrary to other signals, that are deferred until the
437 perl interpreter reaches a reasonably stable state; see
438 L<perlipc/"Deferred Signals (Safe Signals)">). (Rafael)
440 When a module or a file is loaded through an @INC-hook, and when this hook
441 has set a filename entry in %INC, __FILE__ is now set for this module
442 accordingly to the contents of that %INC entry. (Rafael)
444 The C<-w> and C<-t> switches can now be used together without messing
445 up what categories of warnings are activated or not. (Rafael)
447 Duping a filehandle which has the C<:utf8> PerlIO layer set will now
448 properly carry that layer on the duped filehandle. (Rafael)
450 =head1 New or Changed Diagnostics
454 Two deprecation warnings have been added: (Rafael)
456 Opening dirhandle %s also as a file
457 Opening filehandle %s also as a directory
459 =head1 Changed Internals
461 The anonymous hash and array constructors now take 1 op in the optree
462 instead of 3, now that pp_anonhash and pp_anonlist return a reference to
463 an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
465 =for p5p XXX have we some docs on how to create regexp engine plugins, since that's now possible ? (perlreguts)
467 =for p5p XXX new BIND SV type, #29544, #29642
469 =head1 Known Problems
471 =head2 Platform Specific Problems
473 =head1 Reporting Bugs
475 If you find what you think is a bug, you might check the articles
476 recently posted to the comp.lang.perl.misc newsgroup and the perl
477 bug database at http://rt.perl.org/rt3/ . There may also be
478 information at http://www.perl.org/ , the Perl Home Page.
480 If you believe you have an unreported bug, please run the B<perlbug>
481 program included with your release. Be sure to trim your bug down
482 to a tiny but sufficient test case. Your bug report, along with the
483 output of C<perl -V>, will be sent off to perlbug@perl.org to be
484 analysed by the Perl porting team.
488 The F<Changes> file for exhaustive details on what changed.
490 The F<INSTALL> file for how to build Perl.
492 The F<README> file for general stuff.
494 The F<Artistic> and F<Copying> files for copyright information.