[p5sagit/p5-mst-13.2.git] / pod / perl595delta.pod

=head1 NAME

perldelta - what is new for perl v5.9.5

=head1 DESCRIPTION

This document describes differences between the 5.9.4 and the 5.9.5
development releases. See L<perl590delta>, L<perl591delta>,
L<perl592delta>, L<perl593delta> and L<perl594delta> for the differences
between 5.8.0 and 5.9.4.

=head1 Incompatible Changes

=head1 Core Enhancements

=head2 Regular expressions

=over 4

=item Recursive Patterns

It is now possible to write recursive patterns without using the C<(??{})>
construct. This new way is more efficient, and in many cases easier to
read.

Each capturing parenthesis can now be treated as an independent pattern
that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
"parenthesis number"). For example, the following pattern will match
nested balanced angle brackets:

    /
     ^                      # start of line
     (                      # start capture buffer 1
	<                   #   match an opening angle bracket
	(?:                 #   match one of:
	    (?>             #     don't backtrack over the inside of this group
		[^<>]+      #       one or more non angle brackets
	    )               #     end non backtracking group
	|                   #     ... or ...
	    (?1)            #     recurse to bracket 1 and try it again
	)*                  #   0 or more times.
	>                   #   match a closing angle bracket
     )                      # end capture buffer one
     $                      # end of line
    /x

Note, users experienced with PCRE will find that the Perl implementation
of this feature differs from the PCRE one in that it is possible to
backtrack into a recursed pattern, whereas in PCRE the recursion is
atomic or "possessive" in nature.

=item Named Capture Buffers

It is now possible to name capturing parenthesis in a pattern and refer to
the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
It's possible to backreference to a named buffer with the C<< \k<NAME> >>
syntax. In code, the new magical hash C<%+> can be used to access the
contents of the buffers.

Thus, to replace all doubled chars, one could write

    s/(?<letter>.)\k<letter>/$+{letter}/g

Only buffers with defined contents will be "visible" in the hash, so
it's possible to do something like

    foreach my $name (keys %+) {
        print "content of buffer '$name' is $+{$name}\n";
    }

Users exposed to the .NET regex engine will find that the perl
implementation differs in that the numerical ordering of the buffers
is sequential, and not "unnamed first, then named". Thus in the pattern

   /(A)(?<B>B)(C)(?<D>D)/

$1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
$1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
would expect. This is considered a feature. :-)

=item Possessive Quantifiers

Perl now supports the "possessive quantifier" syntax of the "atomic match" 
pattern. Basically a possessive quantifier matches as much as it can and never
gives any back. Thus it can be used to control backtracking. The syntax is 
similar to non-greedy matching, except instead of using a '?' as the modifier
the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
quantifiers.

=back

=head1 Modules and Pragmas

=head2 New Core Modules

=head1 Utility Changes

=head1 Documentation

=head1 Performance Enhancements

=head1 Installation and Configuration Improvements

=head1 Selected Bug Fixes

=head1 New or Changed Diagnostics

=head1 Changed Internals

=head1 Known Problems

=head2 Platform Specific Problems

=head1 Reporting Bugs

If you find what you think is a bug, you might check the articles
recently posted to the comp.lang.perl.misc newsgroup and the perl
bug database at http://rt.perl.org/rt3/ .  There may also be
information at http://www.perl.org/ , the Perl Home Page.

If you believe you have an unreported bug, please run the B<perlbug>
program included with your release.  Be sure to trim your bug down
to a tiny but sufficient test case.  Your bug report, along with the
output of C<perl -V>, will be sent off to perlbug@perl.org to be
analysed by the Perl porting team.

=head1 SEE ALSO

The F<Changes> file for exhaustive details on what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=cut
Commit	Line	Data
f6eae373	1	=head1 NAME
	2
	3	perldelta - what is new for perl v5.9.5
	4
	5	=head1 DESCRIPTION
	6
	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.
	11
	12	=head1 Incompatible Changes
	13
	14	=head1 Core Enhancements
	15
072f65b4	16	=head2 Regular expressions
	17
	18	=over 4
	19
	20	=item Recursive Patterns
	21
	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
	24	read.
	25
	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:
	30
	31	/
	32	^ # start of line
	33	( # start capture buffer 1
	34	< # match an opening angle bracket
	35	(?: # match one of:
	36	(?> # don't backtrack over the inside of this group
	37	[^<>]+ # one or more non angle brackets
	38	) # end non backtracking group
	39	\| # ... or ...
	40	(?1) # recurse to bracket 1 and try it again
	41	)* # 0 or more times.
	42	> # match a closing angle bracket
	43	) # end capture buffer one
	44	$ # end of line
	45	/x
	46
	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.
	51
	52	=item Named Capture Buffers
	53
	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.
	59
	60	Thus, to replace all doubled chars, one could write
	61
	62	s/(?<letter>.)\k<letter>/$+{letter}/g
	63
	64	Only buffers with defined contents will be "visible" in the hash, so
	65	it's possible to do something like
	66
	67	foreach my $name (keys %+) {
	68	print "content of buffer '$name' is $+{$name}\n";
	69	}
	70
	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
	74
	75	/(A)(?<B>B)(C)(?<D>D)/
	76
	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. :-)
80
b9b4dddf	81	=item Possessive Quantifiers
	82
	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
	88	quantifiers.
	89
072f65b4	90	=back
072f65b4	91
f6eae373	92	=head1 Modules and Pragmas
	93
	94	=head2 New Core Modules
	95
	96	=head1 Utility Changes
	97
	98	=head1 Documentation
	99
	100	=head1 Performance Enhancements
	101
	102	=head1 Installation and Configuration Improvements
	103
	104	=head1 Selected Bug Fixes
	105
	106	=head1 New or Changed Diagnostics
	107
	108	=head1 Changed Internals
	109
	110	=head1 Known Problems
	111
	112	=head2 Platform Specific Problems
	113
	114	=head1 Reporting Bugs
	115
	116	If you find what you think is a bug, you might check the articles
	117	recently posted to the comp.lang.perl.misc newsgroup and the perl
	118	bug database at http://rt.perl.org/rt3/ . There may also be
	119	information at http://www.perl.org/ , the Perl Home Page.
	120
	121	If you believe you have an unreported bug, please run the B<perlbug>
	122	program included with your release. Be sure to trim your bug down
	123	to a tiny but sufficient test case. Your bug report, along with the
	124	output of C<perl -V>, will be sent off to perlbug@perl.org to be
	125	analysed by the Perl porting team.
	126
	127	=head1 SEE ALSO
	128
	129	The F<Changes> file for exhaustive details on what changed.
	130
	131	The F<INSTALL> file for how to build Perl.
	132
	133	The F<README> file for general stuff.
	134
	135	The F<Artistic> and F<Copying> files for copyright information.
	136
	137	=cut