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;
}
