Perl::CriticPerl::Critic::Policy::RegularExpressions::ProhibitUnusedCapture(3)NAMEPerl::Critic::Policy::RegularExpressions::ProhibitUnusedCapture - Only
use a capturing group if you plan to use the captured value.
AFFILIATION
This Policy is part of the core Perl::Critic distribution.
DESCRIPTION
Perl regular expressions have multiple types of grouping syntax. The
basic parentheses (e.g. "m/(foo)/") captures into the magic variable
$1. Non-capturing groups (e.g. "m/(?:foo)/" are useful because they
have better runtime performance and do not copy strings to the magic
global capture variables.
It's also easier on the maintenance programmer if you consistently use
capturing vs. non-capturing groups, because that programmer can tell
more easily which regexps can be refactored without breaking
surrounding code which may use the captured values.
CONFIGURATION
This Policy is not configurable except for the standard options.
CAVEATS
"qr//" interpolation
This policy can be confused by interpolation of "qr//" elements, but
those are always false negatives. For example:
my $foo_re = qr/(foo)/;
my ($foo) = m/$foo_re (bar)/x;
A human can tell that this should be a violation because there are two
captures but only the first capture is used, not the second. The
policy only notices that there is one capture in the regexp and remains
happy.
"@-", "@+", $LAST_MATCH_START and $LAST_MATCH_END
This policy will only recognize capture groups referred to by these
variables if the use is subscripted by a literal integer.
$^N and $LAST_SUBMATCH_RESULT
This policy will not recognize capture groups referred to only by these
variables, because there is in general no way by static analysis to
determine which capture group is referred to. For example,
m/ (?: (A[[:alpha:]]+) | (N\d+) ) (?{$foo=$^N}) /smx
makes use of the first capture group if it matches, or the second
capture group if the first does not match but the second does.
CREDITS
Initial development of this policy was supported by a grant from the
Perl Foundation.
AUTHOR
Chris Dolan <cdolan@cpan.org>
COPYRIGHT
Copyright (c) 2007-2011 Chris Dolan. Many rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself. The full text of this license can
be found in the LICENSE file included with this module
perl v5.14.1Perl::Critic::Policy::RegularExpressions::ProhibitUnusedCapture(3)
