Michael Fawcett <michael.fawcett <at> gmail.com> writes:
Contrived example using theoretical code:
// Multiply accumulate (Is there a simpler way?) template < typename X, typename Y, typename Z, typename VX, typename VY, typename VZ
struct macc { // X * VX + Y * VY + Z * VZ typedef typename boost::result_of_multiplies<X, VX>::type x_times_x; typedef typename boost::result_of_multiplies<Y, VY>::type y_times_y; typedef typename boost::result_of_multiplies<Z, VZ>::type z_times_z; typedef typename boost::result_of_plus<y_times_y, z_times_z>::type y_times_y_plus_z_times_z; typedef typename boost::result_of_plus<x_times_x, y_times_y_plus_z_times_z>::type x_plus_y_plus_z; typedef x_plus_y_plus_z type; };
template < typename X, typename Y, typename Z, typename VX, typename VY, typename VZ
typename macc<X, Y, Z, VX, VY, VZ>::type dot_product(const vec3<X, Y, Z> &lhs, const vec3<VX, VY, VZ> &rhs) { return lhs.x * rhs.x + lhs.y * rhs.y + lhs.z * rhs.z; }
Yes, surely a matrix library written like this could do the trick for PQS. But it has its limitations too - see my other comment below.
This would require the math library be more heavily templated than it currently is. Note that a matrix would need to hold mutliple types (up to NxN). For instance, what would be the syntax for a 3D transform? Perhaps something like:
matrix4x4 < float, float, float, length, float, float, float, length, float, float, float, length, length, length, length, float
m;
But consider the following situation (which, though it may sound contrived, is pretty similar to what came up in my real application), Suppose I have a compile-time constant like const int NUM_OF_ITEMS = 5; And I need a vector containing 3 dimensionless quantities, a time, and NUM_OF_ITEMS length values. And then I need a scaling matrix for that! Yes, the value "5" is known a priori, and I could write out the whole 10x10 transform. But I've defined NUM_OF_ITEMS as a symbolic constant because it's subject to change. Next month I find out we have 7 items instead of 5. I'd like it to be a single-point code change: const int NUM_OF_ITEMS = 7; Can I get the compiler to generate the 12x12 matrix definition for me? I bet it's theoretically possible with template metaprogramming, but I doubt it would be worth anybody's time to implement such a monster. This is the point where I threw up my hands and accepted that I was going to need the t3_quantity. -- Leland