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        my $var = shift;                        # wrong
        my($var) = @_;                          # right
        sub foo { uc $_[0] }                    # OK
        my($var1, $var2) = (shift, shift);      # Um, no.

use Benchmark qw(cmpthese);

...
  x_copy1 => 'x_copy1(@args)',
  x_copy2 => 'x_copy2(@args)'
});

             Rate x_copy2 x_copy1 x_shift
x_copy2  609756/s      --    -18%    -45%
x_copy1  746269/s     22%      --    -32%
x_shift 1098901/s     80%     47%      --

use Benchmark qw(cmpthese);

sub x_shift { my $a = shift }
...
my @args = (1 .. 3);

cmpthese(1000000, { x_shift => 'x_shift(@args)', x_copy => 'x_copy(@ar
+gs)' });

             Rate  x_copy x_shift
x_copy  1298701/s      --     -0%
x_shift 1298701/s      0%      --