Sample Autoload function for WordPress plugin

gistfile1.php

<?php
	/**
	 * Plugin autoloader. Coverts class name to path and loads it
	 * @param string $className
	 */
	function autoload($className)
	{
		if (class_exists($className))
			return;

		if (self::$pluginAbsolutePath == NULL)
			self::$pluginAbsolutePath = WP_PLUGIN_DIR . DIRECTORY_SEPARATOR
				. 'foo' . DIRECTORY_SEPARATOR;

		$medium = str_replace('bar', 'classes', strtolower($className));
		$path = str_replace('_', DIRECTORY_SEPARATOR, $medium);

		// Putting altogether
		$path = self::$pluginAbsolutePath . $path . '.php';

		if (file_exists($path) and is_readable($path))
			require_once $path;
	}