Re: Lies, Damn Lies and Benchmarks

[ysth]

I'm not sure what your final point is? Doing this:

cmpthese( -2,{
 list => sub { &list },
 shiftit => sub { &shiftit },
} );

seems just plain broken, and I wouldn't have been surprised if it even made Benchmark roll over and die. You shouldn't be making any assumptions about what is in @_ in your outer sub {}, much less modifiying it.

Trying this:

use Benchmark 'cmpthese';
cmpthese(1, { tryit => sub { $save = \@_ }});
use Data::Dumper;
$Data::Dumper::Deparse = 1;
print Dumper $save;
__END__
$VAR1 = [
          1,
          sub {
                  $save = \@_;
              }
        ];

shows that in fact, cmpthese's parameters are still in @_, and doing:

cmpthese 3, { tryit => sub { push @save, [@_]; shift } };
print Dumper \@save;
$VAR1 = [
          [
            3,
            sub {
                  push @save, [@_];
                  shift @_;
              }
          ],
          [
            $VAR1->[0][1]
          ],
          []
        ];

shows that your shift has blown them away after the first 2 iterations.

[xdg]

The final example isn't a recommendation -- it's an explanation of why the original benchmark was doing what it did and why it was giving counterintuitive results. Though I'll agree that it probably could have used a "don't try this at home" kind of warning, given the implications of the PERLSUB excerpt.