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