PHP: Autoloading Objects

Autoloading Objects

Many developers writing object-oriented applications create one PHP source file per-class definition. One of the biggest annoyances is having to write a long list of needed includes at the beginning of each script (one for each class).

In PHP 5, this is no longer necessary. You may define an __autoload function which is automatically called in case you are trying to use a class/interface which hasn't been defined yet. By calling this function the scripting engine is given a last chance to load the class before PHP fails with an error.

Note: Exceptions thrown in __autoload function cannot be caught in the catch block and results in a fatal error.

Note: Autoloading is not available if using PHP in CLI interactive mode.

Note: If the class name is used e.g. in call_user_func() then it can contain some dangerous characters such as ../. It is recommended to not use the user-input in such functions or at least verify the input in __autoload().

Example #1 Autoload example

This example attempts to load the classes MyClass1 and MyClass2 from the files MyClass1.php and MyClass2.php respectively.


<?php

function __autoload($class_name) {

    require_once $class_name . '.php';

}



$obj  = new MyClass1();

$obj2 = new MyClass2(); 

?>

This example attempts to load the interface ITest.


<?php



function __autoload($name) {

    var_dump($name);

}



class Foo implements ITest {

}



/*

string(5) "ITest"



Fatal error: Interface 'ITest' not found in ...

*/

?>