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package Perl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef;
use 5.010001;
use strict;
use warnings;
use Readonly;
use Perl::Critic::Utils qw{ :severities :classification };
use parent 'Perl::Critic::Policy';
our $VERSION = '1.156';
#-----------------------------------------------------------------------------
Readonly::Scalar my $DESC => q{"return" statement with explicit "undef"};
Readonly::Scalar my $EXPL => [ 199 ];
#-----------------------------------------------------------------------------
sub supported_parameters { return () }
sub default_severity { return $SEVERITY_HIGHEST }
sub default_themes { return qw(core pbp bugs certrec ) }
sub applies_to { return 'PPI::Token::Word' }
#-----------------------------------------------------------------------------
sub violates {
my ( $self, $elem, undef ) = @_;
return if $elem->content() ne 'return';
return if is_hash_key($elem);
my $sib = $elem->snext_sibling();
return if !$sib;
return if !$sib->isa('PPI::Token::Word');
return if $sib->content() ne 'undef';
# Must be 'return undef'
return $self->violation( $DESC, $EXPL, $elem );
}
1;
__END__
#-----------------------------------------------------------------------------
=pod
=head1 NAME
Perl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef - Return failure with bare C<return> instead of C<return undef>.
=head1 AFFILIATION
This Policy is part of the core L<Perl::Critic|Perl::Critic>
distribution.
=head1 DESCRIPTION
Returning C<undef> upon failure from a subroutine is pretty common.
But if the subroutine is called in list context, an explicit C<return
undef;> statement will return a one-element list containing
C<(undef)>. Now if that list is subsequently put in a boolean context
to test for failure, then it evaluates to true. But you probably
wanted it to be false.
sub read_file {
my $file = shift;
-f $file || return undef; #file doesn't exist!
#Continue reading file...
}
#and later...
if ( my @data = read_file($filename) ){
# if $filename doesn't exist,
# @data will be (undef),
# but I'll still be in here!
process(@data);
}
else{
# This is my error handling code.
# I probably want to be in here
# if $filename doesn't exist.
die "$filename not found";
}
The solution is to just use a bare C<return> statement whenever you
want to return failure. In list context, Perl will then give you an
empty list (which is false), and C<undef> in scalar context (which is
also false).
sub read_file {
my $file = shift;
-f $file || return; #DWIM!
#Continue reading file...
}
=head1 CONFIGURATION
This Policy is not configurable except for the standard options.
=head1 NOTES
You can fool this policy pretty easily by hiding C<undef> in a boolean
expression. But don't bother trying. In fact, using return values to
indicate failure is pretty poor technique anyway. Consider using
C<die> or C<croak> with C<eval>, or the L<Error|Error> module for a
much more robust exception-handling model. Conway has a real nice
discussion on error handling in chapter 13 of PBP.
=head1 SEE ALSO
There's a discussion of the appropriateness of this policy at
L<http://perlmonks.org/index.pl?node_id=741847>.
=head1 AUTHOR
Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>
=head1 COPYRIGHT
Copyright (c) 2005-2011 Imaginative Software Systems. All 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
# Local Variables:
# mode: cperl
# cperl-indent-level: 4
# fill-column: 78
# indent-tabs-mode: nil
# c-indentation-style: bsd
# End:
# ex: set ts=8 sts=4 sw=4 tw=78 ft=perl expandtab shiftround :
|
