Option<T>

Option.java

import java.util.Iterator;
import java.util.NoSuchElementException;


/**
 * Implements support for an option type.
 * <pre>
 * // assuming Option<T> foo()
 * 
 * for (T t : foo()) {
 * 		doSomething(t);
 * 		return;
 * } 
 * doDefaultThing();
 * </pre>
 * 
 * @author jseymour
 * @inspiredBy http://eng.wealthfront.com/2010/05/better-option-for-java.html
 * @param <T>
 */
public abstract class Option<T>
	implements Iterable<T>, Cloneable
{
	private static class Impl<T> extends Option<T> implements Iterator<T> {
		
		enum State {
			INIT,
			ITERATOR,
			HAS_NEXT,
			NEXT			
		}
		
		private final T value;
		private State state = State.INIT; 		
		
		public Impl(T value) {
			this.value = value;
		}

		public boolean hasNext() {
			switch (state) {
				case HAS_NEXT: 
				case ITERATOR:
					state = State.HAS_NEXT;
					return value != null;
				default:
					return false;
			}
		}
		
		public T next() {
			if (state != State.HAS_NEXT || value == null) {
				throw new NoSuchElementException("illegal state: attempt to use option with checking for existence first");
			}
			state = State.NEXT;
			return value;
		}
		
		public void remove() {
			throw new UnsupportedOperationException();
		}

		public Iterator<T> iterator() {
			state = State.ITERATOR;
			return this;
		}
		
		public Option<T> clone()
		{
			return new Impl<T>(value);
		}		
	}
	
	public static <T> Option<T> some(T value)
	{
		return new Impl<T>(value);
	}
}