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

Thanks for the compare script. Indeed the lexical is a bit faster (probably what tobyink said about internal optimisations) and is confirmed by choroba but when I declare a lexical variable inside the loop for my $x (1,2,3) {my $z=12; $y+=$x } in predecl, it's 50% slower :(

I keep what you said about optimisation is a science

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Re^3: declaring lexical variables in shortest scope: performance?
by choroba (Cardinal) on Mar 31, 2020 at 11:27 UTC
    > it's 50% slower

    Do you mean you added the my $z=12; to both the subroutines and the lexical one became 50% slower? I can't reproduce that behaviour. Adding it to only one of the subs slows it (35% in my case), but then we are comparing apples and oranges.

    map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
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      I meant to say that comparing lexicals only: one with a my $z; inside the loop is so much slower. Even 35% is much

      here is the code:

      use Benchmark 'cmpthese';

cmpthese(-2, {
    predecl => '
        my $y;
        my $x;
        for $x (1..10000) { $y+=$x }
    #print "$y\n";
    ',
    lexical => '
        my $y;
        for my $x (1..10000) { $y+=$x }
    #print "$y\n";
    ',
});

__END__

      [download]
                Rate predecl lexical
predecl 1836/s      --    -54%
lexical 3996/s    118%      --

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