static array in templated struct/class

[ddos via Digitalmars-d-learn]

alias Vec4f = TVector!(float,4);
alias Vec3f = TVector!(float,3);

class TVector(T,int n)
{
	T[n] val;
...

TVector as class does work as expected, as a struct i get the 
following errors, but why?

struct Vector.TVector!(float, 4).TVector no size yet for forward 
reference
struct Vector.TVector!(float, 3).TVector no size yet for forward 
reference