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PHP autoload机制(lazy loading)

Jun 23, 2016 pm 02:30 PM

Wikipedia:Lazy loading is a design pattern commonly used in computer programming to defer initialization of an object until the point at which it is needed. It can contribute to efficiency in the program's operation if properly and appropriately used. The opposite of lazy loading is eager loading

 

在使用PHP进行开发时,开发者往往将一个类存放在单独的一个文件中,便于使用和管理。

但是在PHP5之前,每次使用一个类时,需要先将该文件include或require进来,如果需要使用的类数量很多,那么需要写很多include或require语句,既麻烦又不便于维护。好在PHP5提供了一种lazy loading的机制,即autoload。

 

PHP5之前如果要使用class A:

require ('A.php');$a = A();
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PHP5中在试图使用未定义的类时会自动调用__autoload函数,可以通过编写__autoload函数让php自动加载类,而不必写一个长长的包含文件列表。

function __autoload($class)  {      $file = $class . '.php';      if (is_file($file)) {          require_once($file);      }  }  $a = new A();
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当然,我们可以自定义__autoload加载类的规则。

此外,假如我们不想自动加载的时候调用__autoload,而是调用我们自己的函数(或者类方法),我们可以使用spl_autoload_register来注册我们自己的autoload函数。

function loader($class)  {      $file = $class . '.php';      if (is_file($file)) {           require_once($file);      }  }  spl_autoload_register('loader');  $a = new A();
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类方法:

class Loader  {     public static function loadClass($class)     {         $file = $class . '.php';         if (is_file($file)) {            require_once($file);         }     }  }  spl_autoload_register(array('Loader', 'loadClass'));  $a = new A();
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