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.

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.

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 ...
*/
?>

Example #3 Autoloading with exception handling

This example throws an exception and demonstrates the try/catch block.

<?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";
}
?>

The above example will output:

Want to load NonLoadableClass.
Unable to load NonLoadableClass.

Example #4 Autoloading with exception handling - Missing custom exception

This example throws an exception for a non-loadable, custom exception.

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

try {
    
$obj = new NonLoadableClass();
} catch (
Exception $e) {
    echo 
$e->getMessage(), "\n";
}
?>

The above example will output:

Want to load NonLoadableClass.
Want to load MissingException.

Fatal error: Class 'MissingException' not found in testMissingException.php on line 4