GSP
Quick Navigator

Search Site

Unix VPS
A - Starter
B - Basic
C - Preferred
D - Commercial
MPS - Dedicated
Previous VPSs
* Sign Up! *

Support
Contact Us
Online Help
Handbooks
Domain Status
Man Pages

FAQ
Virtual Servers
Pricing
Billing
Technical

Network
Facilities
Connectivity
Topology Map

Miscellaneous
Server Agreement
Year 2038
Credits
 

USA Flag

 

 

Man Pages


Manual Reference Pages  -  PERL::CRITIC::POLICY::CONTROLSTRUCTURES::PROHIBITMUTATINGLISTFUNCTIONS (3)

.ds Aq ’

NAME

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

CONTENTS

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.

Search for    or go to Top of page |  Section 3 |  Main Index


perl v5.20.3 PERL::CRITIC::POLICY::CONTROLSTRUCTURES::PROHIBITMUTATINGLISTFUNCTIONS (3) 2016-04-03

Powered by GSP Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.