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1=head1 NAME
2
3perldelta - what is new for perl v5.9.4
4
5=head1 DESCRIPTION
6
7This document describes differences between the 5.9.3 and the 5.9.4
a1889f3a 8development releases. See L<perl590delta>, L<perl591delta>, L<perl592delta>
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9and L<perl593delta> for the differences between 5.8.0 and 5.9.3.
10
11=head1 Incompatible Changes
12
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13=head2 chdir FOO
14
473aa102 15A bareword argument to chdir() is now recognized as a file handle.
4db748fd 16Earlier releases interpreted the bareword as a directory name.
21a732f3 17(Gisle Aas)
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19=head2 Handling of pmc files
20
b7d91234 21An old feature of perl was that before C<require> or C<use> look for a
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22file with a F<.pm> extension, they will first look for a similar filename
23with a F<.pmc> extension. If this file is found, it will be loaded in
24place of any potentially existing file ending in a F<.pm> extension.
ddc61b51 25
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26Previously, F<.pmc> files were loaded only if more recent than the
27matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
28they exist. (This trick is used by Pugs.)
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29
30=head2 @- and @+ in patterns
31
32The special arrays C<@-> and C<@+> are no longer interpolated in regular
21a732f3 33expressions. (Sadahiro Tomoyuki)
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35=head2 $AUTOLOAD can now be tainted
36
37If you call a subroutine by a tainted name, and if it defers to an
38AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
21a732f3 39(Rick Delaney)
5d121f7f 40
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41=head1 Core Enhancements
42
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43=head2 state() variables
44
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45A new class of variables has been introduced. State variables are similar
46to C<my> variables, but are declared with the C<state> keyword in place of
a1889f3a 47C<my>. They're visible only in their lexical scope, but their value is
3c1cb5e0 48persistent: unlike C<my> variables, they're not undefined at scope entry,
a1889f3a 49but retain their previous value. (Rafael Garcia-Suarez)
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50
51To use state variables, one needs to enable them by using
52
53 use feature "state";
54
55or by using the C<-E> command-line switch in one-liners.
56
57See L<perlsub/"Persistent variables via state()">.
58
d06a6528 59=head2 UNIVERSAL::DOES()
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61The C<UNIVERSAL> class has a new method, C<DOES()>. It has been added to
62solve semantic problems with the C<isa()> method. C<isa()> checks for
a1889f3a 63inheritance, while C<DOES()> has been designed to be overridden when
3c1cb5e0 64module authors use other types of relations between classes (in addition
21a732f3 65to inheritance). (chromatic)
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66
67See L<< UNIVERSAL/"$obj->DOES( ROLE )" >>.
68
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69=head2 Exceptions in constant folding
70
71The constant folding routine is now wrapped in an exception handler, and
72if folding throws an exception (such as attempting to evaluate 0/0), perl
73now retains the current optree, rather than aborting the whole program.
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74(Nicholas Clark, Dave Mitchell)
75
76=head2 Source filters in @INC
77
78It's possible to enhance the mechanism of subroutine hooks in @INC by
79adding a source filter on top of the filehandle opened and returned by the
80hook. This feature was planned a long time ago, but wasn't quite working
81until now. See L<perlfunc/require> for details. (Nicholas Clark)
82
83=head2 MAD
84
85MAD, which stands for I<Misc Attribute Decoration>, is a
86still-in-development work leading to a Perl 5 to Perl 6 convertor. To
87enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
88obtained perl isn't binary compatible with a regular perl 5.9.4, and has
89space and speed penalties; moreover not all regression tests still pass
90with it. (Larry Wall, Nicholas Clark)
21a732f3 91
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92=head1 Modules and Pragmata
93
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94=over 4
95
96=item *
97
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98C<encoding::warnings> is now a lexical pragma. (Although on older perls,
99which don't have support for lexical pragmas, it keeps its global
21a732f3 100behaviour.) (Audrey Tang)
6c20a8f9 101
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102=item *
103
104C<threads> is now a dual-life module, also available on CPAN. It has been
105expanded in many ways. A kill() method is available for thread signalling.
106One can get thread status, or the list of running or joinable threads.
107
108A new C<< threads->exit() >> method is used to exit from the application
109(this is the default for the main thread) or from the current thread only
110(this is the default for all other threads). On the other hand, the exit()
111built-in now always causes the whole application to terminate. (Jerry
112D. Hedden)
113
114=back
ddc61b51 115
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116=head2 New Core Modules
117
118=over 4
119
120=item *
121
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122C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
123provides support for I<field hashes>: hashes that maintain an association
124of a reference with a value, in a thread-safe garbage-collected way.
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125
126=item *
127
21a732f3 128C<Module::Build>, by Ken Williams, has been added. It's an alternative to
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129C<ExtUtils::MakeMaker> to build and install perl modules.
130
131=item *
132
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133C<Module::Load>, by Jos Boumans, has been added. It provides a single
134interface to load Perl modules and F<.pl> files.
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135
136=item *
137
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138C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
139modules as loaded or unloaded.
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140
141=item *
142
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143C<Package::Constants>, by Jos Boumans, has been added. It's a simple
144helper to list all constants declared in a given package.
6c20a8f9 145
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146=item *
147
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148C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
149This module provides low-level access to Win32 system API calls for
150files/dirs.
d06a6528 151
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152=back
153
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154=head1 Utility Changes
155
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156=head2 config_data
157
158C<config_data> is a new utility that comes with C<Module::Build>. It
159provides a command-line interface to the configuration of Perl modules
160that use Module::Build's framework of configurability (that is,
161C<*::ConfigData> modules, that contain local configuration information for
162their parent modules.)
163
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164=head1 Documentation
165
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166=head2 New manpage, perlpragma
167
473aa102 168The L<perlpragma> manpage documents how to write one's own lexical
a1889f3a 169pragmas in pure Perl (something that is possible starting with 5.9.4).
473aa102 170
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171=head2 New manpage, perlreguts
172
a1889f3a 173The L<perlreguts> manpage, courtesy of Yves Orton, describes internals of the
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174Perl regular expression engine.
175
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176=head2 New manpage, perlunitut
177
473aa102 178The L<perlunitut> manpage is an tutorial for programming with Unicode and
a1889f3a 179string encodings in Perl, courtesy of Juerd Waalboer.
473aa102 180
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181=head1 Performance Enhancements
182
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183=head2 Memory optimisations
184
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185Several internal data structures (typeglobs, GVs, CVs, formats) have been
186restructured to use less memory. (Nicholas Clark)
187
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188=head2 UTF-8 cache optimisation
189
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190The UTF-8 caching code is now more efficient, and used more often.
191(Nicholas Clark)
192
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193=head2 Regular expressions
194
195=over 4
196
a1889f3a 197=item Engine de-recursiveised
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198
199The regular expression engine is no longer recursive, meaning that
200patterns that used to overflow the stack will either die with useful
201explanations, or run to completion, which, since they were able to blow
202the stack before, will likely take a very long time to happen. If you were
203experiencing the occasional stack overflow (or segfault) and upgrade to
204discover that now perl apparently hangs instead, look for a degenerate
b7d91234 205regex. (Dave Mitchell)
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206
207=item Single char char-classes treated as literals
208
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209Classes of a single character are now treated the same as if the character
210had been used as a literal, meaning that code that uses char-classes as an
211escaping mechanism will see a speedup. (Yves Orton)
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212
213=item Trie optimisation of literal string alternations
214
215Alternations, where possible, are optimised into more efficient matching
216structures. String literal alternations are merged into a trie and are
217matched simultaneously. This means that instead of O(N) time for matching
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218N alternations at a given point the new code performs in O(1) time. (Yves
219Orton)
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220
221B<Note:> Much code exists that works around perl's historic poor
222performance on alternations. Often the tricks used to do so will disable
223the new optimisations. Hopefully the utility modules used for this purpose
224will be educated about these new optimisations by the time 5.10 is
225released.
226
227=item Aho-Corasick start-point optimisation
228
229When a pattern starts with a trie-able alternation and there aren't
230better optimisations available the regex engine will use Aho-Corasick
b7d91234 231matching to find the start point. (Yves Orton)
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232
233=back
6c20a8f9 234
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235=head1 Installation and Configuration Improvements
236
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237=head2 Relocatable installations
238
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239There is now Configure support for creating a relocatable perl tree. If
240you Configure with C<-Duserelocatableinc>, then the paths in @INC (and
241everything else in %Config) can be optionally located via the path of the
242perl executable.
243
244That means that, if the string C<".../"> is found at the start of any
245path, it's substituted with the directory of $^X. So, the relocation can
246be configured on a per-directory basis, although the default with
247C<-Duserelocatableinc> is that everything is relocated. The initial
248install is done to the original configured prefix.
21a732f3 249
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250=head2 Ports
251
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252Many improvements have been made towards making Perl work correctly on
253z/OS.
254
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255Perl has been reported to work on DragonFlyBSD.
256
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257=head2 Compilation improvements
258
259All F<ppport.h> files in the XS modules bundled with perl are now
21a732f3 260autogenerated at build time. (Marcus Holland-Moritz)
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261
262=head2 New probes
263
3c1cb5e0 264The configuration process now detects whether strlcat() and strlcpy() are
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265available. When they are not available, perl's own version is used (from
266Russ Allbery's public domain implementation). Various places in the perl
a1889f3a 267interpreter now use them. (Steve Peters)
ddc61b51 268
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269=head1 Selected Bug Fixes
270
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271=head2 PERL5SHELL and tainting
272
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273On Windows, PERL5SHELL is now checked for taintedness. (Rafael
274Garcia-Suarez)
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275
276=head2 Using *FILE{IO}
277
278C<stat()> and C<-X> filetests now treat *FILE{IO} filehandles like *FILE
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279filehandles. (Steve Peters)
280
281=head2 Overloading and reblessing
282
283Overloading now works when references are reblessed into another class.
284Internally, this has been implemented by moving the flag for "overloading"
285from the reference to the referent, which logically is where it should
286always have been. (Nicholas Clark)
287
288=head2 Overloading and UTF-8
289
290A few bugs related to UTF-8 handling with objects that have
291stringification overloaded have been fixed. (Nicholas Clark)
473aa102 292
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293=head1 New or Changed Diagnostics
294
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295=over 4
296
297=item State variable %s will be reinitialized
298
299One can assign initial values to state variables, but not when they're
300declared as a sub-part of a list assignment. See L<perldiag>.
301
302=back
303
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304=head1 Changed Internals
305
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306A new file, F<mathoms.c>, contains functions that aren't used anymore in
307the perl core, but that remain around because modules out there might
308still use them. They come from a factorization effort: for example, many
309PP functions are now shared for several ops.
6c20a8f9 310
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311The implementation of the special variables $^H and %^H has changed, to
312allow implementing lexical pragmas in pure perl.
313
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314=head1 Known Problems
315
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316One warning test (number 263 in F<lib/warnings.t>) fails under UTF-8
317locales.
318
a1889f3a 319Bytecode tests fail under several platforms. We are considering removing
b7d91234 320support for byteloader and compiler before the 5.10.0 release.
6c7deadb 321
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322=head2 Platform-specific Problems
323
324The test F<ext/Socket/t/socketpair.t> crashes after completing all tests
325successfully when built with USE_ITHREADS and PERL_IMPLICIT_SYS on Win32.
326
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327=head1 Reporting Bugs
328
329If you find what you think is a bug, you might check the articles
330recently posted to the comp.lang.perl.misc newsgroup and the perl
36d7017e 331bug database at http://rt.perl.org/rt3/ . There may also be
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332information at http://www.perl.org/ , the Perl Home Page.
333
334If you believe you have an unreported bug, please run the B<perlbug>
335program included with your release. Be sure to trim your bug down
336to a tiny but sufficient test case. Your bug report, along with the
337output of C<perl -V>, will be sent off to perlbug@perl.org to be
338analysed by the Perl porting team.
339
340=head1 SEE ALSO
341
342The F<Changes> file for exhaustive details on what changed.
343
344The F<INSTALL> file for how to build Perl.
345
346The F<README> file for general stuff.
347
348The F<Artistic> and F<Copying> files for copyright information.
349
350=cut