Standard PHP Library (SPL)

The Standard PHP Library (SPL) is a collection of interfaces and classes that are meant to solve common problems.

SPL offers features, functions, classes and interfaces in many different fields : iterators, data structures, files, exceptions, and observers.

One of the most famous SPL features is the function spl_autoload_register(), which register an autoload handler.

<?php

// SPL and autoloading
spl_autoload_register(function ($class) {
    include 'classes/' . $class . '.class.php';
});

if ($object instanceof Countable) {
    $count = count($object);
} elseif ($object instanceof Traversable)
    $count = iterator_count($object);
} else {
    print "Can't count this";
}

?>

Documentation

Related : Class Autoloading