__autoload vs spl_autoload_register

__autoload() 用于自动加载资源来取代一大堆的 require
在 PHP 的文档 Autoloading Classes 中 首先建议的是使用 spl_autoload_register(), 并且描述到:

Whilst the __autoload() function can also be used for autoloading classes and interfaces, its preferred to use the spl_autoload_register() function. This is because it is a more flexible alternative (enabling for any number of autoloaders to be specified in the application, such as in third party libraries). For this reason, using __autoload() is discouraged and it may be deprecated in the future.

spl_autoload_register() 的文档中提到:

Register a function with the spl provided __autoload queue. If the queue is not yet activated it will be activated.

从这些说明可以看出, spl_autoload_register() 和 __autoload() 比较, 有如下好处:

• 可以灵活的指定某个函数为 “autoloaders”
• 可以指定多个 “loader”, 使这些 “loader” 按顺序执行

从 Autoloading Classes 的另外的 Note:

Prior to PHP 5.3, exceptions thrown in the __autoload() function could not be caught in the catch block and would result in a fatal error. From PHP 5.3 and upwards, this is possible provided that if a custom exception is thrown, then the custom exception class is available. The __autoload() function may be used recursively to autoload the custom exception class.

和 它的 Example #3

<?php
spl_autoload_register(function ($name) {
    echo "Want to load $name.\n";
    throw new Exception("Unable to load $name.");
});

try {
    $obj = new NonLoadableClass();
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}
// 输出如下:
// Want to load NonLoadableClass.
// Unable to load NonLoadableClass.
?>

可以看出 spl_autoload_register() 有更友好的错误处理能力

再配合上 spl_autoload_unregister() 就更加灵活了

参考:

Stackoverflow: someone explain spl_autoload, __autoload and spl_autoload_register?
PHP SPL autoload vs. __autoload
SPL Autoload