use Benchmark 'cmpthese';
use strict;

my %hash = 1 .. 10_000;
my %add = 9_001 .. 11_000;

cmpthese(-5, {
  BASE => sub {
    my %copy = %hash;
  },
  JAPHY => sub {
    my %copy = %hash;
    my @new = grep !exists $copy{$_}, keys %add;
    @copy{@new} = @add{@new};
  },
  ZAXO => sub {
    my %copy = %hash;
    %copy = (%add, %copy);
  },
  NULL => sub {
    my %copy = %hash;
    %copy = (%copy);
  },
});

##</code><code>##

        Rate  ZAXO  NULL JAPHY  BASE
ZAXO  15.1/s    --  -22%  -61%  -76%
NULL  19.3/s   28%    --  -50%  -69%
JAPHY 38.9/s  157%  101%    --  -38%
BASE  62.4/s  312%  223%   60%    --

##</code><code>##

        Rate  ZAXO  NULL JAPHY  BASE
ZAXO  11.4/s    --  -39%  -58%  -81%
NULL  18.6/s   63%    --  -31%  -69%
JAPHY 26.9/s  136%   45%    --  -56%
BASE  60.5/s  431%  225%  125%    --