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Perl::Critic:Perl::CriUser:ContributedrPerlnDocumentationxplicitReturnUndef(3)

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.

perl v5.24.1 Perl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef(3)

NAME | AFFILIATION | DESCRIPTION | CONFIGURATION | NOTES | SEE ALSO | AUTHOR | COPYRIGHT

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