use Data::Dumper;

my @x = qw( foo bar );
print       q[ map { if (0) { $_ } } @x ], "\n";
print Dumper [ map { if (0) { $_ } } @x ];

print "\n", q[ grep 0, @x ], "\n";
print Dumper [ grep 0, @x ];

print "\n", q[ map { 0 ? $_ : () } @x ], "\n";
print Dumper [ map { 0 ? $_ : () } @x ];
__END__
 map { if (0) { $_ } } @x
$VAR1 = [ 
          0,
          0
        ];

 grep 0, @x
$VAR1 = [];

 map { 0 ? $_ : () } @x
$VAR1 = [];