package test;

public class Base<T,BACK,IMPL extends Base<T,BACK,IMPL>>
{
	private final T value;
	private final BACK back;

	public Base(T value, BACK back)
	{
		this.value = value;
		this.back = back;
	}
	
	public BACK pop()
	{
		return back;
	}
	
	public T value()
	{
		return value;
	}
	
	public static void main(String[] args) throws Exception
	{
		new A<>("a", null)				// A<?,?>
			.push(Boolean.TRUE)			// B<A<?,?>,?>	
				.push("a")				// A<B<A<?,?>,?>,?>
					.push(Boolean.TRUE)	// B<A<B<A<?,?>,?>,?>,?>
						.push("a")		// A<B<A<B<A<?,?>,?>,?>,?>,?>
						.pop()			// !code completion shows B<BACK,IMPL> as type returned by pop() 
					.pop()				// !code completion shows BACK as type returned by pop()
				.pop()					// !compiler error: "The method pop() is undefined for the type BACK"
			.pop()
		.pop();
	}
}

class A<BACK,IMPL extends A<BACK,IMPL>> extends Base<String,BACK,IMPL>
{
	public A(String value, BACK back)
	{
		super(value, back);
	}
	
	@SuppressWarnings("unchecked")
	public B<IMPL,?> push(Boolean b)
	{
		return new B<>(b, (IMPL)this);
	}
}

class B<BACK,IMPL extends B<BACK,IMPL>> extends Base<Boolean,BACK,IMPL>
{
	public B(Boolean value, BACK back)
	{
		super(value, back);
	}
	
	@SuppressWarnings("unchecked")
	public A<IMPL,?> push(String s)
	{
		return new A<>(s, (IMPL)this);
	}
}