Multiple Tuple IFTI Syntactic Sugar

[Christopher Wright]

dsimcha wrote:
> I've been thinking about how IFTI works for variadic function templates.  I
> use variadic functions heavily in the infotheory module of dstats, and am
> looking to add some features here.  Currently, my mutual information function
> looks like:
> 
> real mutualInfo(T, U)(T[] x, U[] y);
> 
> I'd like to generalize this so that both x and y can be any number of vectors,
> yielding in standard mathematical notation, something like I(x, y; z, a),
> which is the mutual information of (x, y) as a joint distribution with (z, a)
> as a joint distribution.  However, trying to turn this into D code with decent
> notation leads to some headaches:
> 
> real mutualInfo(T..., U...)(T x, U y);

How do you instantiate that?
mutualInfo!(TypeTuple!(T1, T2, T3), TypeTuple!(T4, T5, T6))?

No, the tuples would be flattened.

Bearophile's suggestion can be implemented something like:
struct MutualInfo(T...)
{
	T x;
	auto opCall(U...)(U y) {}
}
MutualInfo!(T...) mutualInfo(T...)(T args)
{
	// etc
}