Singleton Pattern in ActionScript 3

Here is the current implementation of the singleton pattern I use in ActionScript 3.0:

	package {
	public final class Singleton {
	/**
	* Storage for the singleton instance.
	*/
	public static const instance:Singleton = new Singleton ( SingletonLock );

	/**
	* Constructor
	*
	* @param lock The Singleton lock class to pevent outside instantiation.
	*/
	public function Singleton(lock:Class) {
	// Verify that the lock is the correct class reference.
	if ( lock != SingletonLock ) {
	throw new Error( "Invalid Singleton access. Use Singleton.instance." );
	}
	}

	public static function getInstance():Singleton {
	return Singleton.instance;
	}
	}
	}

	/**
	* This is a private class declared outside of the package
	* that is only accessible to classes inside of the Singleton.as
	* file. Because of that, no outside code is able to get a
	* reference to this class to pass to the constructor, which
	* enables us to prevent outside instantiation.
	*/
	internal class SingletonLock { }

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Rob Morgan