Cross product template

[Diggory]

On Wednesday, 15 May 2013 at 01:31:43 UTC, Diggory wrote:
> I have a vector struct, Vector(T, uint N) templated on the type 
> T and number of components, N. I'm trying to write a function 
> "cross" which will calculate the cross product of a number of 
> vectors.
>
> For a given number of components, N, the cross function should 
> take N-1 arguments, each one a Vector!(?, N) and will return a 
> vector perpendicular to the vectors passed in. The ? means the 
> type is free to be anything.
>
> The problem is that however I try to write it, the template 
> argument deduction isn't powerful enough to work out which 
> instantiation to use.
>
> I thought something like this would work to deduce the 
> parameters and then I could use constraints to enforce the 
> other rules, but no:
> auto cross(T, N, U...)(Vector!(T, N) a, U b) { return 0; }

Well, after much trial and error I ended up with this, which 
seems to work:

template VectorN(T : Vector!(T, N), uint N) {
	enum VectorN = N;
}

template isVectorN(uint N) {
	template isVectorN(T) {
		enum isVectorN = VectorN!(T) == N;
	}
}

auto cross(T...)(T args) if (allSatisfy!(isVectorN!(T.length+1), 
T) && T.length) {
	return 0;
}