リストの要素数を数えるコードの速度比較 ref: http://qiita.com/items/5a00636dbf812722c959

file1.txt

               Rate empty_assign       array  anon_array        grep       alias
empty_assign 7.68/s           --         -2%        -10%        -17%        -39%
array        7.84/s           2%          --         -9%        -15%        -37%
anon_array   8.57/s          12%          9%          --         -7%        -31%
grep         9.21/s          20%         18%          8%          --        -26%
alias        12.5/s          63%         60%         46%         36%          --

list_count.pl

#!/usr/bin/env perl

use strict;
use warnings;
use Benchmark qw/cmpthese/;

sub get_list { 1 .. 1_000_000 }

cmpthese(
  -5,
  +{
    q/alias/ => sub { sub { 0 + @_ }->(get_list) },
    q/anon_array/ => sub { 0 + @{[get_list]} },
    q/array/ => sub { 0 + (my @ary = get_list) },
    q/empty_assign/ => sub { scalar (() = get_list) },
    q/grep/ => sub { scalar grep 1, get_list },
  }
);