Perl::Critic::Policy::RegularExpressions::ProhibitUnusedCapture(3pm)
                                           User Contributed Perl Documentation


NAME
       Perl::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.

   split()
       Normally, this policy thinks that if a capture is used at all it must
       be used before the next regular expression in the same scope. The
       regular expression in a split() needs to be exempted because it does
       not affect the caller's capture variables.

       At present, this policy recognizes and exempts the regular expressions
       in

           split /.../, ...

       and

           split( /.../, ... )

       but more exotic syntax may produce false positives.

CREDITS
       Initial development of this policy was supported by a grant from the
       Perl Foundation.

AUTHOR
       Chris Dolan <cdolan@cpan.org>

COPYRIGHT
       Copyright (c) 2007-2023 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 v5.38.0                      2023-07-26
          Perl::Critic::Policy::RegularExpressions::ProhibitUnusedCapture(3pm)