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Perl:Perl::Critic::PolUser:ContributedcPerlsDocumentationatingListFunctions(3)

NAME
       Perl::Critic::Policy::ControlStructures::ProhibitMutatingListFunctions
       - Don't modify "$_" in list functions.

AFFILIATION
       This Policy is part of the core Perl::Critic distribution.

DESCRIPTION
       "map", "grep" and other list operators are intended to transform	arrays
       into other arrays by applying code to the array elements	one by one.
       For speed, the elements are referenced via a $_ alias rather than
       copying them.  As a consequence,	if the code block of the "map" or
       "grep" modify $_	in any way, then it is actually	modifying the source
       array.  This IS technically allowed, but	those side effects can be
       quite surprising, especially when the array being passed	is @_ or
       perhaps "values(%ENV)"!	Instead	authors	should restrict	in-place array
       modification to "for(@array) { ... }" constructs	instead, or use
       "List::MoreUtils::apply()".

CONFIGURATION
       By default, this	policy applies to the following	list functions:

	   map grep
	   List::Util qw(first)
	   List::MoreUtils qw(any all none notall true false firstidx
			      first_index lastidx last_index insert_after
			      insert_after_string)

       This list can be	overridden the .perlcriticrc file like this:

	   [ControlStructures::ProhibitMutatingListFunctions]
	   list_funcs =	map grep List::Util::first

       Or, one can just	append to the list like	so:

	   [ControlStructures::ProhibitMutatingListFunctions]
	   add_list_funcs = Foo::Bar::listmunge

LIMITATIONS
       This policy deliberately	does not apply to "for (@array)	{ ... }" or
       "List::MoreUtils::apply()".

       Currently, the policy only detects explicit external module usage like
       this:

	   my @out = List::MoreUtils::any {s/^foo//} @in;

       and not like this:

	   use List::MoreUtils qw(any);
	   my @out = any {s/^foo//} @in;

       This policy looks only for modifications	of $_.	Other naughtiness
       could include modifying $a and $b in "sort" and the like.  That's
       beyond the scope	of this	policy.

SEE ALSO
       There is	discussion of this policy at
       <http://perlmonks.org/index.pl?node_id=743445>.

AUTHOR
       Chris Dolan <cdolan@cpan.org>

       Michael Wolf <MichaelRWolf@att.net>

COPYRIGHT
       Copyright (c) 2006-2011 Chris Dolan.

       This program is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

perl Perl::Critic::Policy::ControlStructures::ProhibitMutatingListFunctions(3)

NAME | AFFILIATION | DESCRIPTION | CONFIGURATION | LIMITATIONS | SEE ALSO | AUTHOR | COPYRIGHT

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