list_and_undef_in_return.pl

#! /usr/bin/perl

###############################################################################
# Why you should not use return undef in every situation?
# - In list context it became an array w/ one member, and it's true
# - In scalar context it became UNDEF, and it's false
# - If you are not sure, use the { return wantarray ? : ; }
#                      or simple { return; }
#
# - The same goes with 0 and empty string
###############################################################################

use strict;
use warnings;
use Data::Dumper;

###############################################################################
my @a;

sub returnCheck_1() { return undef; }
sub returnCheck_2() { return (); }
sub returnCheck_3() { return wantarray ? () : undef; }
sub returnCheck_4() { my @a; return @a; }
sub returnCheck_5() {
    my @a = qw(pqs local stocek kinai vcs izlelo hentes wikinger MAGIC w35 kurdisztan hoztam_magammal);
    undef(@a);
    return @a;
}
sub returnCheck_6() { return; }

#------------------------------------------------------------------------------
warn "The   \@a = { undef; }   is an array with one member and \$a[0] == undef\n";
@a = returnCheck_1();
warn Data::Dumper::Dumper(\@a) . "\n";
warn "\@a in boole enviroment becomes: " . (@a ? 'true' : 'false') . "\n\n";


warn '-' x 80 . "\n";
#------------------------------------------------------------------------------
warn "The   \@a = { (); }   is an empty array\n";
@a = returnCheck_2();
warn Data::Dumper::Dumper(\@a) . "\n";
warn "\@a in boole enviroment becomes: " . (@a ? 'true' : 'false') . "\n\n";


warn '-' x 80 . "\n";
#------------------------------------------------------------------------------
warn "The   \@a = { wantarray ? () : undef; }    is an empty array or an undef\n";
@a = returnCheck_3();
warn Data::Dumper::Dumper(\@a) . "\n";
warn "\@a in boole enviroment becomes: " . (@a ? 'true' : 'false') . "\n\n";


warn '-' x 80 . "\n";
#------------------------------------------------------------------------------
warn "The   \@a = { my \@arr; return \@arr; }      is a NOT DEFINED array\n";
@a = returnCheck_4();
warn Data::Dumper::Dumper(\@a) . "\n";
warn "\@a in boole enviroment becomes: " . (@a ? 'true' : 'false') . "\n\n";


warn '-' x 80 . "\n";
#------------------------------------------------------------------------------
warn "The   \@a = { undef(\@arr); return \@arr; }  is an UNDEFINED array\n";
@a = returnCheck_5();
warn Data::Dumper::Dumper(\@a) . "\n";
warn "\@a in boole enviroment becomes: " . (@a ? 'true' : 'false') . "\n\n";


warn '-' x 80 . "\n";
#------------------------------------------------------------------------------
warn "The   \@a = { return; }                    is an UNDEFINED return value\n";
@a = returnCheck_6();
warn Data::Dumper::Dumper(\@a) . "\n";
warn "\@a in boole enviroment becomes: " . (@a ? 'true' : 'false') . "\n\n";
my @b;