Demonstrates how to autoload classes in PHP, so that we don't have to explicitly require each file for each class used within our code

.Autoload.php

<?php
/**
 * Uses the `spl_autoload_register` function to autoload classes so that we don't have to 
 * explicitly require each file for each class we use in our code
 */

_0.lots_of_requires.php

<?php
/**
 * This looks silly, don't you agree?
 */

# make sure we have all the classes we might need, just in case!
require_once 'My_Class.php';
require_once 'My_Second_Class.php';
require_once 'My_Third_Class.php';
require_once 'My_Fourth_Class.php';
require_once 'My_Fifth_Class.php';
require_once 'My_Sixth_Class.php';

# ... somewhere within our code, use My_Class
$my_object = new My_Class();

# ... somewhere else in our code, use My_Fifth_Class
$my_fifth_object = new My_Fifth_Class();

# ... etc ...

_1.autoload.legacy.php

<?php
/**
 * Prior to PHP 5.1.2, autoloading basically worked like this.
 * 
 * Note that this method only lets us have one function to specify autoloading behavior, which
 * will certainly not work within a larger PHP framework with multiple components that may
 * be written by multiple people.
 */
 
# define a function to autoload a file based on the class name being instantiated
function __autoload( $class_name ) {
	
	/**
	 * Note we are just looking for a PHP file with the same name as the class in question.
	 * actual usage may require some string operations to specify the filename
	 */
	$file_name = $class_name . '.php';

	if( file_exists( $file_name ) ) {
		require $file_name;
	}
}

/**
 * Now, we can instantiate a class without explicitly requiring the corresponding file. Note 
 * we would need to have a file called `My_Class.php` in the same directory as this script.
 */
$my_object = new My_Class();

_2.spl_autoload_register_1.php

<?php
/**
 * Example 1: Using an anonymous function as the single parameter for `spl_autoload_register`
 * 
 * @see http://php.net/manual/en/functions.anonymous.php
 */
spl_autoload_register( function( $class_name ) {

	/**
	 * Note that actual usage may require some string operations to specify the filename
	 */
	$file_name = $class_name . '.php';

	if( file_exists( $file_name ) ) {
		require $file_name;
	}
} );

/**
 * ... anywhere in our code, we can now get a new My_Class object without caring whether
 * the class's file has been required or not.
 * 
 * Note in this case we need to have a file called `My_Class.php` in the same directory as this script.
 */
$object = new My_Class();
$object->do_stuff();

_3.spl_autoload_register_2.php

<?php
/**
 * Example 2: Using a string as the single parameter for `spl_autoload_register`
 *
 * We need to define a function with the same name as the string we provide
 *
 * @see	http://php.net/manual/en/language.types.callable.php
 */
spl_autoload_register( 'my_autoload_register' );

/**
 * This function has the same name as the string we passed in above, and acts 
 * exactly the same as the anonymous function from Example 1.
 */
function my_autoload_register( $class_name ) {

	/** etc **/
}

_4.spl_autoload_register_3.php

<?php
/**
 * Example 3: Using additional parameters for `spl_autoload_register`
 *
 * @param $throw = true		Optionally turn off exception throwing
 * @param $prepend = false	Optionally add our function to the beginning of the autoload queue
 */

/**
 * Between the two functions being registered, `other_autoload_register` will get called first, even
 * though it is being registered second, because it uses the $prepend parameter.
 */
spl_autoload_register( 'my_autoload_register' );
spl_autoload_register( 'other_autoload_register', null, true );