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Re: Lies, Damn Lies and Benchmarks

by ysth (Canon)
on Mar 21, 2004 at 23:59 UTC ( #338527=note: print w/ replies, xml ) Need Help??


in reply to Lies, Damn Lies and Benchmarks

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.


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Re: Re: Lies, Damn Lies and Benchmarks
by xdg (Monsignor) on Mar 22, 2004 at 15:38 UTC

    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.

    -xdg

    Code posted by xdg on PerlMonks is public domain. It has no warranties, express or implied. Posted code may not have been tested. Use at your own risk.

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