Re^3: Dereferencing in blessed object

[bliako]

$$vars{'test'} is a visual pain for me because of the split millisecond where I ask myself about precedence. OTH the -> in $vars->{'test'} dates back to at least C where is used in exactly the same way and context.

Performance-wise I don't think there is a difference (OSX 10.13 and perl 5.28.3):

use Benchmark qw( cmpthese );

cmpthese(-5, {
        deref => 'use strict; use warnings; my $x = { map { $_ => rand
+ } 1..50 };
                  $x->{$_} = $_ for 1..100',
        none  => 'use strict; use warnings; my $x = { map { $_ => rand
+ } 1..50 };
                  $$x{$_} = $_ for 1..100'
});

         Rate deref  none
deref 12483/s    --   -1%
none  12611/s    1%    --

         Rate  none deref
none  11938/s    --   -0%
deref 11967/s    0%    --

Or,

use Benchmark qw( cmpthese );

cmpthese(-5, {
    deref => 'use strict; use warnings;
          srand 42;
          my $x = { map { rand() => rand() } 1..50 };
          srand 42;
          $x->{rand()} = rand() for 1..100',
    none  => 'use strict; use warnings;
          srand 42;
          my $x = { map { rand() => rand() } 1..50 };
          srand 42;
          $$x{rand()} = rand() for 1..100'
});

For benchmarks see also: https://stackoverflow.com/questions/18984323/how-expensive-is-it-to-dereference-an-array-ref-in-perl

bw, bliako

[LanX]

> Performance-wise I don't think there is a difference (OSX 10.13 and perl 5.28.3):

That would be surprsing, it's compiled to the same op-code.

C:\WINDOWS\System32>perl -MO=Deparse -e"$$x{key}"
$x->{'key'};
-e syntax OK

C:\WINDOWS\System32>perl -MO=Concise -e"$$x{key}"
4  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter v ->2
2     <;> nextstate(main 1 -e:1) v:{ ->3
-     <1> ex-helem vK/2 ->4
3        <+> multideref($x->{"key"}) vK ->4
-           <0> ex-gv s ->3
-e syntax OK

C:\WINDOWS\System32>perl -MO=Concise -e"$x->{key}"
4  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter v ->2
2     <;> nextstate(main 1 -e:1) v:{ ->3
-     <1> ex-helem vK/2 ->4
3        <+> multideref($x->{"key"}) vK ->4
-           <0> ex-gv s ->3
-e syntax OK

C:\WINDOWS\System32>

[bliako]

Good point!