public class EvenNumbers {
	public int get(int index) {
		return index * 2;
	}

	public bool contains(int i) {
		return i % 2 == 0;
	}

	public string to_string() {
		return "[This object enumerates even numbers]";
	}

	public Iterator iterator() {
		return new Iterator(this);
	}

	public class Iterator {
		private int index;
		private EvenNumbers even;

		public Iterator(EvenNumbers even) {
			this.even = even;
		}

		public bool next() {
			return true;
		}

		public int get() {
			this.index++;
			return this.even[this.index - 1];
		}
	}
}

void main() {
	var even = new EvenNumbers();
	stdout.printf("%d\n", even[5]);
	if (4 in even) {
		stdout.printf(@"$even\n");
	}
	foreach (var i in even) {
		stdout.printf("%d\n", i);
		if (i == 20) break;
	}
}