CT Inheritence structures

[Engine Machine via Digitalmars-d-learn]

I am trying to get Timon Gehr's code working, with some 
modifications:



public template TypeParent(P)
{	
	import std.traits;
	alias T = TemplateArgsOf!P;
	alias Seq(T...) = T;
     static if (T.length == 0 || is(typeof(T[0]) == typeof(null)))
	{
		alias TypeParent = Seq!();		
	}
     else
	{
		alias TypeParent = Seq!(P!(T[0..T.length-1]));
	}
}


class Type(T...) : TypeParent!(Type!T)
{
	int x;
	static if (T.length >= 1 && T[0] is "Animal")
	{
		int y;
		static if (T.length >= 2 && T[1] is "Dog")
		{
			int z;
			static if (T.length >= 3&& T[2] is "Pug")
			{
				int s;
			}
		}

	}
}


void main()
{

	import std.traits;

	auto a = new Type!("Animal", "Dog", "Pug")();
	Type!("Animal", "Dog") b = a;	
	Type!("Animal") c = b;	

	a.s = 1;
	b.z = 2;
	c.y = 3;
}

The problem is that b and c are of type P!

Type!("Animal", "Dog", "Pug")
P!("Animal", "Dog")
P!"Animal"

Of course, P should be Type and b.z and c.y should change a's 
variables.

I don't know why

alias TypeParent = Seq!(P!(T[0..T.length-1]));

is returning P but I guess I'm doing it wrong. What I want is for 
it to return Type!(T[0],...,T[n-1]);

Any ideas?