.\" -*- mode: troff; coding: utf-8 -*-
.\" Automatically generated by Pod::Man 5.01 (Pod::Simple 3.43)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>.
.ie n \{\
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds C`
.    ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\"
.\" If the F register is >0, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.nr rF 0
.if \n(.g .if rF .nr rF 1
.if (\n(rF:(\n(.g==0)) \{\
.    if \nF \{\
.        de IX
.        tm Index:\\$1\t\\n%\t"\\$2"
..
.        if !\nF==2 \{\
.            nr % 0
.            nr F 2
.        \}
.    \}
.\}
.rr rF
.\" ========================================================================
.\"
.IX Title "Perl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef 3pm"
.TH Perl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef 3pm 2023-07-26 "perl v5.38.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
Perl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef \- Return failure with bare "return" instead of "return undef".
.SH AFFILIATION
.IX Header "AFFILIATION"
This Policy is part of the core Perl::Critic
distribution.
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Returning \f(CW\*(C`undef\*(C'\fR upon failure from a subroutine is pretty common.
But if the subroutine is called in list context, an explicit \f(CW\*(C`return
undef;\*(C'\fR statement will return a one-element list containing
\&\f(CW\*(C`(undef)\*(C'\fR.  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.
.PP
.Vb 3
\&  sub read_file {
\&      my $file = shift;
\&      \-f $file || return undef;  #file doesn\*(Aqt exist!
\&
\&      #Continue reading file...
\&  }
\&
\&  #and later...
\&
\&  if ( my @data = read_file($filename) ){
\&
\&      # if $filename doesn\*(Aqt exist,
\&      # @data will be (undef),
\&      # but I\*(Aqll still be in here!
\&
\&      process(@data);
\&  }
\&  else{
\&
\&      # This is my error handling code.
\&      # I probably want to be in here
\&      # if $filename doesn\*(Aqt exist.
\&
\&      die "$filename not found";
\&  }
.Ve
.PP
The solution is to just use a bare \f(CW\*(C`return\*(C'\fR statement whenever you
want to return failure.  In list context, Perl will then give you an
empty list (which is false), and \f(CW\*(C`undef\*(C'\fR in scalar context (which is
also false).
.PP
.Vb 3
\&  sub read_file {
\&      my $file = shift;
\&      \-f $file || return;  #DWIM!
\&
\&      #Continue reading file...
\&  }
.Ve
.SH CONFIGURATION
.IX Header "CONFIGURATION"
This Policy is not configurable except for the standard options.
.SH NOTES
.IX Header "NOTES"
You can fool this policy pretty easily by hiding \f(CW\*(C`undef\*(C'\fR in a boolean
expression.  But don't bother trying.  In fact, using return values to
indicate failure is pretty poor technique anyway.  Consider using
\&\f(CW\*(C`die\*(C'\fR or \f(CW\*(C`croak\*(C'\fR with \f(CW\*(C`eval\*(C'\fR, 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.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
There's a discussion of the appropriateness of this policy at
<http://perlmonks.org/index.pl?node_id=741847>.
.SH AUTHOR
.IX Header "AUTHOR"
Jeffrey Ryan Thalhammer <jeff@imaginative\-software.com>
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright (c) 2005\-2011 Imaginative Software Systems.  All rights reserved.
.PP
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.