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?