Except that you never actually stored anything in local $x.

use Benchmark 'cmpthese';

$x = int (1_000_000 * rand 1_000_000);

cmpthese( -3, {
  mod => sub { $x % 10 },
  chop => sub { local $x; chop $x },
  chop2 => sub { chop(local $x = $x) },
});

__END__

          Rate chop2  chop   mod
chop2  25430/s    --  -88%  -93%
chop  204396/s  704%    --  -41%
mod   348051/s 1269%   70%    --
[download]

On my machine, chop() was slower. But the real chop() approach was slower still.

japhy -- Perl and Regex Hacker