Another PHP typesafe enum idea

TypesafeEnum.php

<?php

/**
 * To create some typesafe enums, just extend this class, declare and initialize
 * to null a protected static property called $values, and implement getNames()
 * to return an array with the enums you want. Then you can access your
 * enums with YourClassName::ENUM_NAME(). Also, your subclass should be final.
 * 
 * Disadvantages:
 * - Usage is ugly.
 * - No IDE autocompletion.
 *
 * Advantages:
 * - Enums can't be modified by mistake (or by malicious code, except via reflection).
 * - No initialization required.
 */
abstract class TypesafeEnum {

	/**
	 * Used in __toString()
	 *
	 * @var string
	 */
	private $name;

	/**
	 * This method should return an array of available enum names.
	 */
	protected abstract static function getNames();

	/**
	 * Called when an enum is requested (actually implemented as unavailable
	 * methods).
	 */
	public static function __callStatic( $calledMethod, $args ) {

		$calledClass = get_called_class();

		// Set up the values the first time an enum from this class is used
		if ( is_null( $calledClass::$values ) ) {

			$calledClass::$values = array();

			foreach ( $calledClass::getNames() as $name ) {
				$calledClass::$values[$name] = new $calledClass( $name );
			}
		}

		// Throw an exception if this enum wasn't defined
		if ( !isset( $calledClass::$values[$calledMethod] ) ) {
			throw new Exception( 'Undefined enum ' . $calledMethod );
		}

		return $calledClass::$values[$calledMethod];
	}

	private function __construct( $name ) {
		$this->name = $name;
	}

	public function __toString() {
		return $this->name;
	}
}

// Example use
final class MyHappyEnum extends TypesafeEnum {

	protected static $values = null;

	protected static function getNames() {
		return array(
			'ENUM_ONE',
			'ENUM_TWO',
			'ENUM_THREE'
		);
	}
}

// Here's the function we'll use to demonstrate
$func = function( MyHappyEnum $enum ) {

	// Got the right class
	print 'Class of parameter is ' . get_class( $enum ) . "\n";

	// __toString() works
	print 'Name is ' . $enum . "\n";

	// Switch also works normally
	switch ( $enum ) {

		case MyHappyEnum::ENUM_ONE():
			print "Switch: one\n";
			break;

		case MyHappyEnum::ENUM_TWO():
			print "Switch: two\n";
			break;

		case MyHappyEnum::ENUM_THREE():
			print "Switch: three\n";
			break;

		default:
			throw new Exception( "Shouldn't happen." );
	}
};

print ( "Testing call with " . MyHappyEnum::ENUM_TWO() . "\n\n" );
$func( MyHappyEnum::ENUM_TWO() );

print ( "\n\nTesting call with " . MyHappyEnum::ENUM_THREE() . "\n\n" );
$func( MyHappyEnum::ENUM_THREE() );

// The following lines cause a fatal error or an exception. Uncomment any one
// to try it.
// $func( new MyHappyEnum( 'Can\'t instantiate anywhere else.' ) );
// $func( 'Type hint prevents passing anything else.' );
// $func( MyHappyEnum::CAN_T_USE_NON_EXISTENT_ENUM() );

Compare to https://gist.github.com/AndrewGreen/9846282