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[perl5.git] / pod / perl595delta.pod
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1=head1 NAME
2
3perldelta - what is new for perl v5.9.5
4
5=head1 DESCRIPTION
6
7This document describes differences between the 5.9.4 and the 5.9.5
8development releases. See L<perl590delta>, L<perl591delta>,
9L<perl592delta>, L<perl593delta> and L<perl594delta> for the differences
10between 5.8.0 and 5.9.4.
11
12=head1 Incompatible Changes
13
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14=head2 Removal of the bytecode compiler and of perlcc
15
16C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
17B::Bytecode, etc.) are no longer distributed with the perl sources. Those
18experimental tools have never worked reliably, and, due to the lack of
19volunteers to keep them in line with the perl interpreter developments, it
20was decided to remove them instead of shipping a broken version of those.
21The last version of those modules can be found with perl 5.9.4.
22
23However the B compiler framework stays supported in the perl core, as with
24the more useful modules it has permitted (among others, B::Deparse and
25B::Concise).
26
27=head2 Removal of the JPL
28
29The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
30
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31=head1 Core Enhancements
32
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33=head2 Regular expressions
34
35=over 4
36
37=item Recursive Patterns
38
39It is now possible to write recursive patterns without using the C<(??{})>
40construct. This new way is more efficient, and in many cases easier to
41read.
42
43Each capturing parenthesis can now be treated as an independent pattern
44that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
45"parenthesis number"). For example, the following pattern will match
46nested balanced angle brackets:
47
48 /
49 ^ # start of line
50 ( # start capture buffer 1
51 < # match an opening angle bracket
52 (?: # match one of:
53 (?> # don't backtrack over the inside of this group
54 [^<>]+ # one or more non angle brackets
55 ) # end non backtracking group
56 | # ... or ...
57 (?1) # recurse to bracket 1 and try it again
58 )* # 0 or more times.
59 > # match a closing angle bracket
60 ) # end capture buffer one
61 $ # end of line
62 /x
63
64Note, users experienced with PCRE will find that the Perl implementation
65of this feature differs from the PCRE one in that it is possible to
66backtrack into a recursed pattern, whereas in PCRE the recursion is
73966613 67atomic or "possessive" in nature. (Yves Orton)
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68
69=item Named Capture Buffers
70
71It is now possible to name capturing parenthesis in a pattern and refer to
72the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
73It's possible to backreference to a named buffer with the C<< \k<NAME> >>
74syntax. In code, the new magical hash C<%+> can be used to access the
75contents of the buffers.
76
77Thus, to replace all doubled chars, one could write
78
79 s/(?<letter>.)\k<letter>/$+{letter}/g
80
81Only buffers with defined contents will be "visible" in the hash, so
82it's possible to do something like
83
84 foreach my $name (keys %+) {
85 print "content of buffer '$name' is $+{$name}\n";
86 }
87
88Users exposed to the .NET regex engine will find that the perl
89implementation differs in that the numerical ordering of the buffers
90is sequential, and not "unnamed first, then named". Thus in the pattern
91
92 /(A)(?<B>B)(C)(?<D>D)/
93
94$1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
95$1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
73966613 96would expect. This is considered a feature. :-) (Yves Orton)
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98=item Possessive Quantifiers
99
100Perl now supports the "possessive quantifier" syntax of the "atomic match"
101pattern. Basically a possessive quantifier matches as much as it can and never
102gives any back. Thus it can be used to control backtracking. The syntax is
103similar to non-greedy matching, except instead of using a '?' as the modifier
104the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
73966613 105quantifiers. (Yves Orton)
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107=item Backtracking control verbs
108
109The regex engine now supports a number of special purpose backtrack
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110control verbs: (*COMMIT), (*MARK), (*CUT), (*ERROR), (*FAIL) and
111(*ACCEPT). See L<perlre> for their descriptions.
24b23f37 112
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113=back
114
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115=head2 The C<_> prototype
116
117A new prototype character has been added. C<_> is equivalent to C<$> (it
118denotes a scalar), but defaults to C<$_> if the corresponding argument
119isn't supplied. Due to the optional nature of the argument, you can only
120use it at the end of a prototype, or before a semicolon.
121
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122This has a small incompatible consequence: the prototype() function has
123been adjusted to return C<_> for some built-ins in appropriate cases (for
124example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
125
126=head2 UCD 5.0.0
127
128The copy of the Unicode Character Database included in Perl 5.9 has
129been updated to version 5.0.0.
130
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131=head1 Modules and Pragmas
132
133=head2 New Core Modules
134
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135=over 4
136
137=item *
138
139C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
140C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
141included in the perl core; the behaviour of C<Locale::Maketext::Simple>
142gracefully degrades when the later isn't present.
143
144=item *
145
146C<Params::Check> implements a generic input parsing/checking mechanism. It
147is used by CPANPLUS.
148
149=back
150
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151=head2 Module changes
152
153=over 4
154
155=item C<base>
156
157The C<base> pragma now warns if a class tries to inherit from itself.
158
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159=item C<warnings>
160
161The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
162that used C<Carp> routines without having loaded it at compile time might
163need to be adjusted; typically, the following (faulty) code won't work
164anymore, and will require parentheses to be added after the function name:
165
166 use warnings;
167 require Carp;
168 Carp::confess "argh";
169
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170=back
171
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172=head1 Utility Changes
173
174=head1 Documentation
175
176=head1 Performance Enhancements
177
178=head1 Installation and Configuration Improvements
179
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180=head2 C++ compatibility
181
182Efforts have been made to make perl and the core XS modules compilable
183with various C++ compilers (although the situation is not perfect with
184some of the compilers on some of the platforms tested.)
185
186=head2 Ports
187
188Perl has been reported to work on MidnightBSD.
189
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190=head1 Selected Bug Fixes
191
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192PerlIO::scalar will now prevent writing to read-only scalars.
193
194study() never worked for UTF-8 strings, but could lead to false results.
195It's now a no-op on UTF-8 data. (Yves Orton)
196
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197=head1 New or Changed Diagnostics
198
199=head1 Changed Internals
200
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201The anonymous hash and array constructors now take 1 op in the optree
202instead of 3, now that pp_anonhash and pp_anonlist return a reference to
203an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
204
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205=head1 Known Problems
206
207=head2 Platform Specific Problems
208
209=head1 Reporting Bugs
210
211If you find what you think is a bug, you might check the articles
212recently posted to the comp.lang.perl.misc newsgroup and the perl
213bug database at http://rt.perl.org/rt3/ . There may also be
214information at http://www.perl.org/ , the Perl Home Page.
215
216If you believe you have an unreported bug, please run the B<perlbug>
217program included with your release. Be sure to trim your bug down
218to a tiny but sufficient test case. Your bug report, along with the
219output of C<perl -V>, will be sent off to perlbug@perl.org to be
220analysed by the Perl porting team.
221
222=head1 SEE ALSO
223
224The F<Changes> file for exhaustive details on what changed.
225
226The F<INSTALL> file for how to build Perl.
227
228The F<README> file for general stuff.
229
230The F<Artistic> and F<Copying> files for copyright information.
231
232=cut