use Data::Dumper;

my @short = (0..2);
my @x = map { ($_, $_) } @short;
print Dumper \@x;
my @y = map ($_, $_), @short;
print Dumper \@y;
__END__
$VAR1 = [ 
          0,
          0,
          1,
          1,
          2,
          2
        ];
$VAR1 = [ 
          undef
        ];