[PHP] __DIR__ vs. dirname(__FILE__)

PHP 5.3 開始支援 __DIR__，從測試中可以知道 __DIR__ 略快于 dirname(__FILE__)。

function calc($t0, $t1)
{
   $v0 = array_sum(explode(' ', $t0));
   $v1 = array_sum(explode(' ', $t1));
   $sub = $v1 - $v0;
   echo "$v1 - $v0 = $sub\n";
   return $sub;
}
$t0 = microtime();
for ($i = 0; $i < 1E6; $i++) require_once __DIR__.'/a.php';
$t1 = microtime();
$new = calc($t0, $t1);     // output: 1420769613.0535 - 1420769612.1561 = 0.89736700057983

$t0 = microtime();
for ($i = 0; $i < 1E6; $i++) require_once dirname(__FILE__).'/a.php';
$t1 = microtime();
$old = calc($t0, $t1);     // output: 1420769614.9498 - 1420769613.0548 = 1.8950188159943

echo ($old - $new) / $old; // output: 0.52646011057731

參考資料：http://www.php.net/manual/en/language.constants.predefined.php

PHP 5.3.24 (cli) (built: Jun 10 2013 16:42:20)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2013 Zend Technologies
    with Xdebug v2.2.0rc1, Copyright (c) 2002-2012, by Derick Rethans