详解PHP文件的自动加载（autoloading）

<?php
require_once('../includes/functions.php');
require_once('../includes/database.php');
require_once('../includes/user.php');
...

<?php
function __autoload($class_name)
{
  require "./{$class_name}.php";
}

<?php
function __autoload($class_name)
{
  $name = strtolower($class_name);
  $path = "../includes/{$name}.php";
  
  if(file_exists($path)){
     require_once($path);
    }else{
      die("the file {$class_name} could not be found");
    }
}

//使用匿名函数来autoload
spl_autoload_register(function($class_name){
  require_once('...');
});

//使用一个全局函数
function Custom()
{
  require_once('...');
}

spl_autoload_register('Custom');

//使用一个class当中的static方法
class MyCustomAutoloader
{
  static public function myLoader($class_name)
  {
    require_once('...');    
  }
}

//传array进来，第一个是class名，第二个是方法名
spl_autoload_register(['MyCustomAutoloader','myLoader']);  

//甚至也可以用在实例化的object上
class MyCustomAutoloader
{
  public function myLoader($class_name)
  {
  }
}

$object = new MyCustomAutoloader;
spl_autoload_register([$object,'myLoader']); 

/**
 * Prepend the load method to the auto-loader stack.
 *
 * @return void
 */
protected function prependToLoaderStack()
{
  spl_autoload_register([$this, 'load'], true, true);
}