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).

In PHP 5, this is no longer necessary. 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.

Tip Although the __autoload() function can also be used for autoloading classes and interfaces, it's 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 deprecated as of PHP 7.2.0.


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.

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.


<?phpspl_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.


<?phpspl_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 for 5.3.0+

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


<?phpspl_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 for 5.3.0+ - Missing custom exception

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


<?phpspl_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