in reply to Re^2: "exists $hash{key}" is slower than "$hash{key}"
in thread "exists $hash{key}" is slower than "$hash{key}"

Thanks for this. The interesting thing is that if I stringify the code to avoid the sub call then I can replicate the ordering from my original post.

I added a false value to get a sense of the cost of the increment operation. value_true is value from your version, and is obviously faster as it does less work.

use warnings;
use strict;
use Benchmark qw{ cmpthese };

my %h;
@h{1001 .. 2000} = (1) x 1000;
my ($e, $vt, $vf) = (0) x 3;
$h{1002} = 0;

cmpthese(-2, {
    exist => sub { for (0..999_999) {   ++$e if exists $h{1001}   } },
    exist_str   => 'for (0..999_999) {   ++$e if exists $h{1001}  }',
    value_true  => sub { for (0..999_999) {   ++$vt if $h{1001}   } },
    value_str   => 'for (0..999_999) {   ++$vt if $h{1001}   }',
    value_false => sub { for (0..999_999) {   ++$vf if $h{1002}   } },
});

__DATA__
              Rate       exist  value_true   exist_str   value_str val
+ue_false
exist       16.1/s          --         -9%        -23%        -26%    
+    -27%
value_true  17.7/s         10%          --        -15%        -18%    
+    -20%
exist_str   20.9/s         29%         18%          --         -4%    
+     -6%
value_str   21.7/s         34%         22%          4%          --    
+     -2%
value_false 22.1/s         37%         25%          6%          2%    
+      --

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Re^4: "exists $hash{key}" is slower than "$hash{key}"
by LanX (Saint) on Jan 07, 2020 at 02:30 UTC
    > if I stringify the code to avoid the sub call then I can replicate the ordering from my original post.

    I'm not sure if you got the point, that accessing an outer lexical variable inside a string is not possible.

    Did you?

    The Benchmark module is eventually running the code's text thru eval , but inside it's own scope.

    The my ($e, $vt, $vf) = (0) x 3; are not accessible from there.

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

[reply]
[d/l]
      > The Benchmark module is eventually running the code's text thru eval , but inside it's own scope.

      Not only that, it also turns off strict, so Perl doesn't tell you the hash you're trying to access doesn't exist. 

      sub _doeval { no strict;  eval shift }

      [download]

      map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
[reply]
[d/l]
[select]

      The point of the exercise is not to access lexical variables. They are used only so something happens in case that code will otherwise be optimised away (I don't know the internals well enough to be sure). I should have been clearer about this in my original post.

[reply]

        But %h is a lexical variable too, and the point of the exercise is to access that.

        toby döt ink
[reply]
[d/l]
        > The point of the exercise is not to access lexical variables.

        But you are measuring them too.

        Cheers Rolf
        (addicted to the Perl Programming Language :)
        Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

[reply]

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