/**
 * A class for lazy-loading other classes
 *
 * This class enables lazy-loading of php classes.  The benefit of this is
 * three-fold.  First, there is a memory benefit, since not all classes are
 * loaded until they are needed.  Second, there is a time benefit, since not all
 * classes are loaded.  Third, it produces cleaner code, since there is no need
     * to litter files with require_once() calls.
 *
 * @category Libraries
 * @package  Libraries
 * @author   Me
 */
abstract class Loader
{

    /**
     * @var array An array of class to path mappings
     */
    protected static $classes = array();

    /**
     * @var boolean Has the loader been initialized already
     */
    protected static $initialized = false;

    /**
     * @var array An array of auto-search paths
     */
    protected static $namedPaths = array(
        'exception',
        'interface',
        'iterator',
    );

    /**
     * @var array An array of include paths to search
     */
    protected static $paths = array(
        PATH_LIBS,
    );

    /**
     * Tell the auto-loader where to find an un-loaded class
     *
     * This can be used to "register" new classes that are unknown to the
     * system.  It can also be used to "overload" a class (redefine it
     * elsewhere)
     *
     * @param string $class The class name to overload
     * @param string $path  The path to the new class
     *
     * @throws InvalidArgumentException Upon an Invalid path submission
     * @return void
     */
    public static function _($class, $path)
    {
        $class = strtolower($class);
        if (!file_exists($path)) {
            throw new InvalidArgumentException('Invalid Path Specified');
        }
        self::$classes[$class] = $path;
    }

    /**
     * Add a path to the include path list
     *
     * This adds a path to the list of paths to search for an included file.
     * This should not be used to overload classes, since the default include
     * directory will always be searched first.  This can be used to extend
     * the search path to include new parts of the system
     *
     * @param string $path The path to add to the search list
     *
     * @throws InvalidArgumentException when an invalid path is specified
     * @return void
     */
    public static function addPath($path)
    {
        if (!is_dir($path)) {
            throw new InvalidArgumentException('Invalid Include Path Added');
        }
        $path = rtrim($path, DS);
        if (!in_array($path, self::$paths)) {
                self::$paths[] = $path;
        }
    }

    /**
     * Add a path to the auto-search paths (for trailing extensions)
     *
     * The path should end with an 's'.  Default files should not.
     *
     * @param string $path The name of the new auto-search path
     *
     * @return void
     */
    public static function addNamedPath($path)
    {
        $path = strtolower($path);
        if (substr($path, -1) == 's') {
            $path = substr($path, 0, -1);
        }
        if (!in_array($path, self::$namedPaths)) {
            self::$namedPaths[] = $path;
        }
    }

    /**
     * Initialize and register the autoloader.
     *
     * This method will setup the autoloader.  This should only be called once.
     *
     * @return void
     */
    public static function initialize()
    {
        if (!self::$initialized) {
            self::$initialized = true;
            spl_autoload_register(array('Loader', 'load'));
        }
    }

    /**
     * The actual auto-loading function.
     *
     * This is automatically called by PHP whenever a class name is used that
     * doesn't exist yet.  There should be no need to manually call this method.
     *
     * @param string $class The class name to load
     *
     * @return void
     */
    public static function load($class)
    {
        $className = strtolower($class);
        if (isset(self::$classes[$className])) {
            $file = self::$classes[$className];
        } else {
            $file = self::findFile($class);
        }
        if (file_exists($file)) {
            include_once $file;
        }
    }

    /**
     * Find the file to include based upon its name
     *
     * This splits the class name by uppercase letter, and then rejoins them
     * to attain the file system path.  So FooBarBaz will be turned into
     * foo/bar/baz.  It then searches the include paths for that chain.  If baz
     * is a directory, it searches that directory for a file called baz.php.
     * Otherwise, it looks for baz.php under the bar directory.
     *
     * @param string $class The name of the class to find
     *
     * @return string The path to the file defining that class
     */
    protected static function findFile($class)
    {
        $regex = '#([A-Z]{1}[a-z0-9_]+)#';
        $options = PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE;
        $parts = preg_split($regex, $class, null, $options);

        $subpath = '';
        $file = strtolower(end($parts));
        $test = strtolower(reset($parts));
        if ($test == 'is') {
            array_shift($parts);
            return self::findNamedFile($class, $parts, 'interface');
        }
        foreach ($parts as $part) {
            $subpath .= DS . strtolower($part);
        }
        foreach (self::$paths as $path) {
            $newpath = $path . $subpath;
            if (is_file($newpath . '.php')) {
                return $newpath . '.php';
            } elseif (is_file($newpath . DS . $file . '.php')) {
                return $newpath . DS . $file . '.php';
            }
        }
        if (in_array($file, self::$namedPaths)) {
            //Get rid of the trailing part
            array_pop($parts);
            return self::findNamedFile($class, $parts, $file);
        }
        return '';
    }

    /**
     * Find a file for named directories (interfaces, exceptions, iterators, etc)
     *
     * @param string $class The class name of the exception to find
     * @param array  $parts The parts of the class name pre-split
     * @param string $name  The name of the named directory to search in
     *
     * @return string The found path, or '' if not found
     */
    protected static function findNamedFile($class, array $parts, $name)
    {
        if (empty($parts)) {
            return '';
        }
        $name = strtolower($name);
        //Add a trailing s, since individual files are not plural
        $filename = $name;
        $name .= 's';
        //Try the global path first
        $subpath = DS . $name . DS . strtolower(implode('', $parts)) . '.php';
        foreach (self::$paths as $path) {
            $newpath = $path . $subpath;
            if (is_file($newpath)) {
                return $newpath;
            }
        }
        //Try to build a full sub path for package specific named files
        $package = array_shift($parts);
        $subpath = DS . strtolower($package) . DS . $name . DS;
        if (!empty($parts)) {
            $subpath .= strtolower(implode('', $parts)) . '.php';
        } else {
            $subpath .= $filename . '.php';
        }
        foreach (self::$paths as $path) {
            $newpath = $path . $subpath;
            if (is_file($newpath)) {
                return $newpath;
            }
        }
        return '';
    }
}

<Vendor Name>(<Namespace>)*<Class Name>

$classLoader = new SplClassLoader('DoctrineCommon', '/libs/doctrine');
$classLoader->register();

$classLoader = new SplClassLoader('IrcmexellMyApplication', 'libs/internal');
$classLoader->register();

pwd
/var/www/project/app
ls -lah PHPE*
PHPExcel -> ../external/PHPExcel/PHPExcel
PHPExcel.php -> ../external/PHPExcel/PHPExcel.php

set_include_path (PATH . 'app');
require 'somepath/Autoloader.php';
Autoloader::registerAutoload ();

class Autoloader
{

public static function registerAutoload ()
{
    spl_autoload_register (array (__CLASS__, 'autoload'));
}

/**
 * @static
 * @param string $class
 * @return void
 */
public static function autoload ($class)
{
    require str_replace (array ('_', '\'), '/', $class) . '.php';
}

public static function registerAutoload ()
{
    spl_autoload_register (array (__CLASS__, 'autoload'));
}

/**
 * @static
 * @param string $class
 * @return void
 */
public static function autoload ($class)
{
    require str_replace (array ('_', '\'), '/', $class) . '.php';
}