Ceylon: Singletons

	/**
	A singleton is the one and only possible instance of a Class. In languages like Java you have to use
	all kinds of crazy patterns to accomplish this.
	See http://en.wikipedia.org/wiki/Singleton_pattern
	Not so in Ceylon however :) You just need to use an algebraic type with a single subtype (object)
	**/
	shared abstract class Earth() of earth {}
	shared object earth extends Earth(){}
	//WON'T COMPILE ==> not a subtype of any case of enumerated supertype: BabyEarth is a subtype of Earth
	//class BabyEarth() extends Earth() {}
	//WON'T COMPILE ==> not a subtype of any case of enumerated supertype: BabyEarth is a subtype of Earth
	//shared object babyEarth extends Earth() {}

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