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.