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 =head1 Core Enhancements
16 =head2 Regular expressions
20 =item Recursive Patterns
22 It is now possible to write recursive patterns without using the C<(??{})>
23 construct. This new way is more efficient, and in many cases easier to
26 Each capturing parenthesis can now be treated as an independent pattern
27 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
28 "parenthesis number"). For example, the following pattern will match
29 nested balanced angle brackets:
33 ( # start capture buffer 1
34 < # match an opening angle bracket
36 (?> # don't backtrack over the inside of this group
37 [^<>]+ # one or more non angle brackets
38 ) # end non backtracking group
40 (?1) # recurse to bracket 1 and try it again
42 > # match a closing angle bracket
43 ) # end capture buffer one
47 Note, users experienced with PCRE will find that the Perl implementation
48 of this feature differs from the PCRE one in that it is possible to
49 backtrack into a recursed pattern, whereas in PCRE the recursion is
50 atomic or "possessive" in nature.
52 =item Named Capture Buffers
54 It is now possible to name capturing parenthesis in a pattern and refer to
55 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
56 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
57 syntax. In code, the new magical hash C<%+> can be used to access the
58 contents of the buffers.
60 Thus, to replace all doubled chars, one could write
62 s/(?<letter>.)\k<letter>/$+{letter}/g
64 Only buffers with defined contents will be "visible" in the hash, so
65 it's possible to do something like
67 foreach my $name (keys %+) {
68 print "content of buffer '$name' is $+{$name}\n";
71 Users exposed to the .NET regex engine will find that the perl
72 implementation differs in that the numerical ordering of the buffers
73 is sequential, and not "unnamed first, then named". Thus in the pattern
75 /(A)(?<B>B)(C)(?<D>D)/
77 $1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
78 $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
79 would expect. This is considered a feature. :-)
81 =item Possessive Quantifiers
83 Perl now supports the "possessive quantifier" syntax of the "atomic match"
84 pattern. Basically a possessive quantifier matches as much as it can and never
85 gives any back. Thus it can be used to control backtracking. The syntax is
86 similar to non-greedy matching, except instead of using a '?' as the modifier
87 the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
92 =head2 The C<_> prototype
94 A new prototype character has been added. C<_> is equivalent to C<$> (it
95 denotes a scalar), but defaults to C<$_> if the corresponding argument
96 isn't supplied. Due to the optional nature of the argument, you can only
97 use it at the end of a prototype, or before a semicolon.
99 =head1 Modules and Pragmas
101 =head2 New Core Modules
103 =head2 Module changes
109 The C<base> pragma now warns if a class tries to inherit from itself.
113 =head1 Utility Changes
117 =head1 Performance Enhancements
119 =head1 Installation and Configuration Improvements
121 =head1 Selected Bug Fixes
123 =head1 New or Changed Diagnostics
125 =head1 Changed Internals
127 =head1 Known Problems
129 =head2 Platform Specific Problems
131 =head1 Reporting Bugs
133 If you find what you think is a bug, you might check the articles
134 recently posted to the comp.lang.perl.misc newsgroup and the perl
135 bug database at http://rt.perl.org/rt3/ . There may also be
136 information at http://www.perl.org/ , the Perl Home Page.
138 If you believe you have an unreported bug, please run the B<perlbug>
139 program included with your release. Be sure to trim your bug down
140 to a tiny but sufficient test case. Your bug report, along with the
141 output of C<perl -V>, will be sent off to perlbug@perl.org to be
142 analysed by the Perl porting team.
146 The F<Changes> file for exhaustive details on what changed.
148 The F<INSTALL> file for how to build Perl.
150 The F<README> file for general stuff.
152 The F<Artistic> and F<Copying> files for copyright information.