@h{<QA>}=undef;

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;
use Benchmark qw(:all :hireswallclock);

foreach my $arraySize(10,100,1_000,10_000,100_000) {
    my @data=map rand,0..$arraySize;

    print "========== ARRAY SIZE: $arraySize\n";

    cmpthese(
            -1,
            {
                '@tmp=@arr' => sub {
                    my @arr = @data;
                    my %h;
                    @h{@arr} = @arr;
                },
                '@tmp=undef' => sub {
                    my @arr = @data;
                    my %h;
                    @h{@arr} = undef;
                },
                'loop=1' => sub {
                    my %h;
                    foreach (@data) {
                        $h{$_} = 1;
                    }
                },
                'loop=undef' => sub {
                    my %h;
                    foreach (@data) {
                        $h{$_} = undef;
                    }
                },
                '@h{@data}=1' => sub {
                    my %h;
                    @h{@data} = 1;
                },
                '@h{@data}=undef' => sub {
                    my %h;
                    @h{@data} = undef;
                },
                'undef @h{@data}' => sub {
                    my %h;
                    undef @h{@data};
                },
            }
        );
}