Question

Core problem:
I want to be able to take an instance of a templated class, say:

template<class a, class b, class c> class foo;

foo<int, float, double>;

and then do something like:

foo<int, float, double>::value;  //Evaluates to a unique number
foo<long, float, double>::value; //Evaluates to a different unique number
foo<int, float, double>::value;  //Evaulates to the same unique number

Except, really, it’s:

template<class a, class b, class c>
int getUniqueIdentifier()
{
    return foo<a, b, c>::value;
} 

Current Solution Attempt:
I’m thinking I want to use Boost::MPL’s “Extensible Associative Sequence”, since each element gets it’s own unique identifier, but I think I need to be able to alter the sequence in place, which “insert” doesn’t do.
I may be barking up the wrong tree. (On the plus side, dayum, but MPL!)

Purpose:
Reinventing the wheel on a Signals & Sockets system. Components make and register channels with a “switchboard”, which would use the unique identifiers to put the channels in a map, allowing run-time versatility. I’ve tried looking up the Qt library as an example, but I can’t parse their abbreviations, and I think I’m missing some formal know-how.

Thanks!

Answer 1

If you want to put things in a map, and need a per-type key, the proper solution is to use std::type_info::before(). It may be worthwhile to derive a class so you can provide operator<, alternatively wrap std::type_info::before() in a binary predicate.