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Re^2: declaring lexical variables in shortest scope: performance?

by Anonymous Monk
on Mar 31, 2020 at 11:50 UTC ( #11114847=note: print w/replies, xml ) Need Help??


in reply to Re: declaring lexical variables in shortest scope: performance?
in thread declaring lexical variables in shortest scope: performance?

Benchmark pitfall, overhead drowns out what you're measuring, in line sub contents as strings not sub calls
  • Comment on Re^2: declaring lexical variables in shortest scope: performance?

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Re^3: declaring lexical variables in shortest scope: performance?
by bliako (Parson) on Mar 31, 2020 at 12:09 UTC

    I didn't know that! Is the logic behind replacing the sub with a string expression, to fool the cache?

    use Benchmark 'cmpthese'; cmpthese(-2, { predecl => ' my $y; my $x; for $x (1..10000) { $y+=$x } ', lexical => ' my $y; for my $x (1..10000) { $y+=$x } ', }); __END__
    Rate lexical predecl lexical 3996/s -- -0% predecl 4001/s 0% --

    vs

    use Benchmark 'cmpthese'; cmpthese(-2, { predecl => sub { my $y; my $x; for $x (1..10000) { $y+=$x } }, lexical => sub { my $y; for my $x (1..10000) { $y+=$x } }, });
    Rate predecl lexical predecl 4011/s -- -0% lexical 4015/s 0% --

    Which is more or less what haukex and choroba demonstrated.

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