On Fri, 21 May 2010 17:50:20 -0400, John Dlugosz wrote:
template<> class message
{ ... } template<> class message { ... } So there is in fact a list of 'PossibleMessages' available to the compiler. It is every argument to a specialisation of class message<Id>. Is there a way I can harvest these to build the PossibleMessages list?
Derive message<T> from a "tag" base class. Then you don't build a list, but you have a predicate to test "is this type in my set?" by using is_base_of, that's perfectly useful for enable_if.
It's building this set that's the problem, not checking if an item is in it. I need a list of all messages IDs (UINTs) that have a message<BLAH> specialisation.
On the other hand, you could use a signature that matches the use of the template:
template<typename Msg> LRESULT on (message<T> m);
will only match this templatized member function if it is indeed a specialization of message.
Yes, this is how my handlers work (except the on() method is not itself a template - does that affect it?).
BTW, I take a different approach to the problem in general. Rather than a zillion individual handlers, I use small "pods" of related messages.
I'm building a native Windows Forms library so the public interface won't actually have any messages at all; only events. The stuff I'm doing now, however, is the intermediate layer so I still have to deal with messages.
For example, handling the mouse messages is a class that handles just a few mouse-related messages, and if you deal with one you probably deal with all. The pods are kept in a linked list, which is searched for suitable handlers.
How do you match the incoming message ID to the pods?
This allows run-time "modes" by updating that list or enabling specific entries that lie dormant. By having different specially declared functions for each Windows message (yet, not a million virtual functions in one class!) each can have a proper signature that wraps its real use, rather than dealing with the raw format.
I'm afraid I don't understand this bit. What do you mean by specially declared functions? Thanks. Alex