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

> 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]

Replies are listed 'Best First'.
Re^4: declaring lexical variables in shortest scope: performance?
by bliako (Abbot) on Mar 31, 2020 at 11:58 UTC

    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%      --

    [download]
[reply]
[d/l]
[select]
[reply]

        what do you mean by aliasing? if you mean accessing complex structures $x->{'a'}->{'b'}->[$loop_index] , I always put the static part of the data structure outside the loop and use that "alias?" inside the loop

[reply]
[d/l]

In Section Seekers of Perl Wisdom