Autoload your classes in PHP

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.

This is how it works in action. We will create two classes. So create Image.php file and paste this in:

1

<?php

2	class Image {

3

4	function __construct() {

5	echo 'Class Image loaded successfully <br />';

6

}

7

8

}

9

?>

Now create Test.php file and paste this in:

1

<?php

2	class Test {

3

4	function __construct() {

5	echo 'Class Test working <br />';

6

}

7

8

}

9

?>

Basically, we created 2 simple classes with constructors which echo some text out. Now, create a file index.php and paste this in:

1

<?php

2	function __autoload($class_name) {

3	require_once $class_name . '.php';

4

}

5

6	$a = new Test();

7	$b = new Image();

8

?>

When you run index.php in browser, everything is working fine (assuming all 3 files are in the same folder). Maybe you don’t see a point, but imagine that you have 10 or more classes and have to write require_once as many times.

I will show you how to properly throw exception if you are using PHP 5.3 and above. Chane your index.php to look like this:

01

<?php

02	function __autoload($class_name) {

03	if(file_exists($class_name . '.php')) {

04	require_once($class_name . '.php');

05

} else {

06	throw new Exception("Unable to load $class_name.");

07

}

08

}

09

10

try {

11	$a = new Test();

12	$b = new Image();

13	} catch (Exception $e) {

14	echo $e->getMessage(), "\n";

15

}

16

?>

Now, it checks if file exists and throws a proper Exception if it doesn’t.