NAME¶
Perl::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.