Chain two different struct specialization

[Andrea Fontana]

On Friday, 1 March 2013 at 14:39:53 UTC, bearophile wrote:
> Andrea Fontana:
>
>> double likeness(T,T1)(ref in T1, ref in T2)
>
> ==>
>
> double likeness(T1, T2)(in ref T1, in ref T2)
>
> Bye,
> bearophile


Sure not the only error. I was writing "pseudo code". Real code 
it's quite complex.

Try this one (is a really reduced working example):

struct MyStruct(WEIGHTS)
{
	this (int p, int p2) { prop = p; prop2 = p2; }
	int prop;
	int prop2;
	
	alias WEIGHTS weights;
}

double likeness(T1,T2)(ref in T1 first, ref in T2 second)
{
	double v = (first.prop - second.prop) * first.weights.foo * 
second.weights.foo;
	v += (first.prop2 - second.prop2) * first.weights.bar * 
second.weights.bar;
	return v;
}

enum FirstWeights : double
{
	foo = 0.3,
	bar = 0.4
}

enum SecondWeights : double
{
	foo = 0.5,
	bar = 0.2
}

void main(string[] args)
{


	auto s1 = MyStruct!FirstWeights(10,8);
	auto s2 = MyStruct!FirstWeights(9, 10);
	auto s3 = MyStruct!SecondWeights(9,10);

	writeln(likeness(s1,s2)); // works
	writeln(likeness(s1,s3)); // works


}

How to put s1,s2,3... in a range/array or something 
similar/iterable? Probably there's no way (inside variant?)...