ELLIOTJS / Perl-Critic-1.083_001 / lib / Perl / Critic / Policy / BuiltinFunctions / ProhibitBooleanGrep.pm 

            

              
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##############################################################################
#      $URL: http://perlcritic.tigris.org/svn/perlcritic/trunk/Perl-Critic/lib/Perl/Critic/Policy/BuiltinFunctions/ProhibitBooleanGrep.pm $
#     $Date: 2008-04-13 20:15:13 -0500 (Sun, 13 Apr 2008) $
#   $Author: clonezone $
# $Revision: 2233 $
##############################################################################
package Perl::Critic::Policy::BuiltinFunctions::ProhibitBooleanGrep;
use strict;
use warnings;
use Readonly;
use Perl::Critic::Utils qw{ :severities :classification hashify };
use base 'Perl::Critic::Policy';
our $VERSION = '1.083_001';
#-----------------------------------------------------------------------------
Readonly::Scalar my $DESC => q{"grep" used in boolean context};
Readonly::Scalar my $EXPL => [71,72];
Readonly::Hash my %POSTFIX_CONDITIONALS => hashify( qw(if unless while until) );
Readonly::Hash my %BOOLEAN_OPERATORS => hashify( qw(&& || ! not or and));
#-----------------------------------------------------------------------------
sub supported_parameters { return ()                     }
sub default_severity     { return $SEVERITY_LOW          }
sub default_themes       { return qw( core pbp performance ) }
sub applies_to           { return 'PPI::Token::Word'     }
#-----------------------------------------------------------------------------
sub violates {
    my ( $self, $elem, undef ) = @_;
    return if $elem ne 'grep';
    return if not is_function_call($elem);
    return if not _is_in_boolean_context($elem);
    return $self->violation( $DESC, $EXPL, $elem );
}
#-----------------------------------------------------------------------------
sub _is_in_boolean_context {
    my ($token) = @_;
    return _does_prev_sibling_cause_boolean($token) || _does_parent_cause_boolean($token);
}
sub _does_prev_sibling_cause_boolean {
    my ($token) = @_;
    my $prev = $token->sprevious_sibling;
    return if !$prev;
    return 1 if $prev->isa('PPI::Token::Word') and $POSTFIX_CONDITIONALS{$prev};
    return if not ($prev->isa('PPI::Token::Operator') and $BOOLEAN_OPERATORS{$prev});
    my $next = $token->snext_sibling;
    return 1 if not $next; # bizarre: grep with no arguments
    # loose heuristic: unparenthesized grep has no following non-boolean operators
    return 1 if not $next->isa('PPI::Structure::List');
    $next = $next->snext_sibling;
    return 1 if not $next;
    return 1 if $next->isa('PPI::Token::Operator') and $BOOLEAN_OPERATORS{$next};
    return;
}
sub _does_parent_cause_boolean {
    my ($token) = @_;
    my $prev = $token->sprevious_sibling;
    return if $prev;
    my $parent = $token->statement->parent;
    for (my $node = $parent; $node; $node = $node->parent) { ##no critic 'CStyleForLoop'
        next if $node->isa('PPI::Structure::List');
        return 1 if $node->isa('PPI::Structure::Condition');
    }
    return;
}
1;
__END__
#-----------------------------------------------------------------------------
=pod
=head1 NAME
Perl::Critic::Policy::BuiltinFunctions::ProhibitBooleanGrep
=head1 DESCRIPTION
Using C<grep> in boolean context is a common idiom for checking if any
elements in a list match a condition.  This works because boolean context is a
subset of scalar context, and grep returns the number of matches in scalar
context.  A non-zero number of matches means a match.
But consider the case of a long array where the first element is a match.
Boolean C<grep> still checks all of the rest of the elements needlessly.
Instead, a better solution is to use the C<any> function from
L<List::MoreUtils>, which short-circuits after the first successful match to
save time.
=head1 CAVEATS
The algorithm for detecting boolean context takes a LOT of shortcuts.  There
are lots of known false negatives.  But, I was conservative in writing this,
so I hope there are no false positives.
=head1 AUTHOR
Chris Dolan <cdolan@cpan.org>
=head1 CREDITS
Initial development of this policy was supported by a grant from the Perl
Foundation.
=head1 COPYRIGHT
Copyright (c) 2007-2008 Chris Dolan.  Many rights reserved.
This program is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.  The full text of this license
can be found in the LICENSE file included with this module.
=cut
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