use-smart-autoload.md

Use Smart Autoload

When it was introduced, class autoloading was build around the function __autoload. When this function is defined, PHP will use it to search for classes definitions if such a definition is missing.

<?php

// example of __autoload
function __autoload($classname) {
    $filename = PROJECT_ROOT.'/'. $classname .'.php';
    include($filename);
}

?>

This way, various libraries may cohabit peacefully. However, the function __autoload also introduces competition for libraries, that needed to provide their own support for the autoloading.

Thus, spl_autoload_register was introduced : it allows the registration of autoloader methods, may it be functions, methods or static methods. They will be played one after each other, giving a chance to every library to have its own fitted autoloading.

It is highly recommended to rely on spl_autoload_register and to avoid defining any __autoload function.

Rule Details

Any usage of __autoload is forbidden.

The following are considered warning :

<?php

// function definition
function __autoload($classname) {
    $filename = PROJECT_ROOT.'/'. $classname .'.php';
    if (file_exists($filename)) {
	    include($filename);
	}
}

?>

The following are considered legit :

<?php

// example adapted from the PHP documentation : 

// registering one's function
function my_autoloader($class) {
    $filename = PROJECT_ROOT.'/'. $classname .'.php';
    if (file_exists($filename)) {
	    include($filename);
	}
}

spl_autoload_register('my_autoloader');


// Or, using an anonymous function as of PHP 5.3.0
spl_autoload_register(function ($class) {
    $filename = PROJECT_ROOT.'/'. $classname .'.php';
    if (file_exists($filename)) {
	    include($filename);
	}
});

?>

When Not To Use It

• If you need to include functions or constants, you can't use autoloading.

Further Reading

• Autoloading Classes ¶
• spl_autoload_register
• __autoload