# benchmark four ways to combine hashes:
cmpthese (-10,{

  forloop => sub {
    for (keys %$hash2) {
        $hash1->{$_} = $hash2->{$_}
    }
  },

  whileach => sub {
      while (my($key, $val) = each %$hash2) {
        $hash1->{$key} = $val;
      }
  },

  slice => sub {
      @$hash1{keys %$hash2} = values %$hash2;
  },

  merge => sub {
    my $hash1 = {%$hash1, %$hash2};
  },

},'auto');