Perl::Critic:Perl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef(3)NAMEPerl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef - Return
failure with bare "return" instead of "return undef".
AFFILIATION
This Policy is part of the core Perl::Critic distribution.
DESCRIPTION
Returning "undef" upon failure from a subroutine is pretty common. But
if the subroutine is called in list context, an explicit "return
undef;" statement will return a one-element list containing "(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 $filname doesn't exist.
die "$filename not found";
}
The solution is to just use a bare "return" statement whenever you want
to return failure. In list context, Perl will then give you an empty
list (which is false), and "undef" in scalar context (which is also
false).
sub read_file {
my $file = shift;
-f $file || return; #DWIM!
#Continue reading file...
}
CONFIGURATION
This Policy is not configurable except for the standard options.
NOTES
You can fool this policy pretty easily by hiding "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 "die"
or "croak" with "eval", or the Error module for a much more robust
exception-handling model. Conway has a real nice discussion on error
handling in chapter 13 of PBP.
SEE ALSO
There's a discussion of the appropriateness of this policy at
<http://perlmonks.org/index.pl?node_id=741847>.
AUTHOR
Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>
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.
perl v5.14.1 Perl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef(3)
