Indexing an associative array with a list of types

[Doctor J]

I'd like to make a compile-time constant associative array mapping a list of 
types to an integer:

int[??] typemap;

typemap[(int,float)] = 1;
typemap[(long,double)] = 2;
...
int t = typemap[(int,float)];

I tried playing with std.typetuple but no luck.  I can get halfway there with a 
function template, but then I can't iterate over the keys or values.  Is there 
a way to do something like this in D?  More generally, is there a way to store 
a type in a variable?

Thanks.