Classes and Objects
PHP Manual

Autoloading Classes

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).

The spl_autoload_register function registers any number of autoloaders, enabling for classes and interfaces to be automatically loaded if they are currently not defined. By registering autoloaders, PHP is given a last chance to load the class or interface before it fails with an error.

Any class-like construct may be autoloaded the same way. That includes classes, interfaces, traits, and enumerations.

Caution

Prior to PHP 8.0.0, it was possible to use __autoload to autoload classes and interfaces. However, it is a less flexible alternative to spl_autoload_register and __autoload is deprecated as of PHP 7.2.0, and removed as of PHP 8.0.0.

Note:

spl_autoload_register may be called multiple times in order to register multiple autoloaders. Throwing an exception from an autoload function, however, will interrupt that process and not allow further autoload functions to run. For that reason, throwing exceptions from an autoload function is strongly discouraged.

Example #1 Autoload example

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

<?php
spl_autoload_register(function ($class_name) {
    include $class_name . '.php';
});

$obj  = new MyClass1();
$obj2 = new MyClass2(); 
?>

Example #2 Autoload other example

This example attempts to load the interface ITest. 

<?php

spl_autoload_register(function ($name) {
    var_dump($name);
});

class Foo implements ITest {
}

/*
string(5) "ITest"

Fatal error: Interface 'ITest' not found in ...
*/
?>

See Also