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DBOOK / Perl-Critic-Freenode-0.026 / lib / Perl / Critic / Policy / Freenode / DollarAB.pm 

            

              
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package Perl::Critic::Policy::Freenode::DollarAB;
use strict;
use warnings;
use Perl::Critic::Utils qw(:severities :classification :ppi);
use parent 'Perl::Critic::Policy';
our $VERSION = '0.026';
use constant DESC => 'Using $a or $b outside sort()';
use constant EXPL => '$a and $b are special package variables for use in sort() and related functions. Declaring them as lexicals like "my $a" may break sort(). Use different variable names.';
sub supported_parameters {
        (
                {
                        name        => 'extra_pair_functions',
                        description => 'Non-standard functions in which to allow $a and $b',
                        behavior    => 'string list',
                },
        )
}
sub default_severity { $SEVERITY_HIGH }
sub default_themes { 'freenode' }
sub applies_to { 'PPI::Token::Symbol' }
my @sorters = qw(sort reduce pairgrep pairfirst pairmap pairwise);
sub violates {
        my ($self, $elem) = @_;
        return () unless $elem->symbol eq '$a' or $elem->symbol eq '$b';
        my %sorters_hash = map { ($_ => 1) } @sorters, keys %{$self->{_extra_pair_functions}};
        my $found = $self->_find_sorter($elem, \%sorters_hash);
         
        return $self->violation(DESC, EXPL, $elem) unless $found;
        return ();
}
sub _find_sorter {
        my ($self, $elem, $sorters) = @_;
         
        my $outer = $elem->parent;
        $outer = $outer->parent until !$outer or $outer->isa('PPI::Structure::Block');
        return '' unless $outer;
         
        # Find function or method call (assumes block/sub is first argument)
        my $function = $outer->previous_token;
        $function = $function->previous_token until !$function
                or ($function->isa('PPI::Token::Word') and $function =~ m/([^:]+)\z/ and exists $sorters->{$1});
        return $self->_find_sorter($outer) unless $function;
        return $function;
}
1;
=head1 NAME
Perl::Critic::Policy::Freenode::DollarAB - Don't use $a or $b as variable names
outside sort
=head1 DESCRIPTION
The special variables C<$a> and C<$b> are reserved for C<sort()> and similar
functions which assign to them to iterate over pairs of values. These are
global variables, and declaring them as lexical variables with C<my> to use
them outside this context can break usage of these functions. Use different
names for your variables.
  my $a = 1;                  # not ok
  my $abc = 1;                # ok
  sort { $a <=> $b } (3,2,1); # ok
=head1 AFFILIATION
This policy is part of L<Perl::Critic::Freenode>.
=head1 CONFIGURATION
This policy can be configured to allow C<$a> and C<$b> in additional functions,
by putting an entry in a C<.perlcriticrc> file like this:
  [Freenode::DollarAB]
  extra_pair_functions = pairfoo pairbar
=head1 AUTHOR
Dan Book, C<dbook@cpan.org>
=head1 COPYRIGHT AND LICENSE
Copyright 2015, Dan Book.
This library is free software; you may redistribute it and/or modify it under
the terms of the Artistic License version 2.0.
=head1 SEE ALSO
L<Perl::Critic>