#!/usr/bin/perl
use strict;
use warnings;
use Benchmark;

Benchmark::cmpthese(-1, {
  bad_1 => \&rx_bad_1,
  bad_2 => \&rx_bad_2,
  good  => \&rx_good,
  good_2  => \&rx_good_2,
  good_3  => \&rx_good_3,
  good_4  => \&rx_good_4
});

sub rx_bad_1 {  for (0..100000) { my $rx = qr/\d+/o; 1 =~ /$rx/; } }
sub rx_bad_2 {  for (0..100000) { my $rx = qr/\d+/;  1 =~ /$rx/o; } }
sub rx_good {   my $rx = qr/\d+/; for (0..100000) { 1 =~ /$rx/o; } }
sub rx_good_2 { my $rx = qr/\d+/; for (0..100000) { 1 =~ /$rx/; } }
sub rx_good_3 { my $rx = '\d+';   for (0..100000) { 1 =~ /$rx/o; } }
sub rx_good_4 { my $rx = '\d+';   for (0..100000) { 1 =~ /$rx/; } }