RE: [boost] Re: method deduction (on vc?)

From: Max Khesin (MKhesin_at_[hidden])
Date: 2004-07-15 09:39:48

> Max Khesin <MKhesin_at_[hidden]> writes:
> 
> > But not (from your phrasing) function members?
> 
> I don't know about those; I haven't tried to find workarounds 
> for that.
> 
> FWIW, designs that depend on member detection are often flawed from a
> generic programming POV.  You can get accidental conformance, and
> especially if there's no way to explicitly say what the member means
> (e.g. with a traits specialization), you'll be out-of-luck.

Well, this is my intent, just for the record, (perhaps there are other
techniques that apply):
I want a generic dispatch function that accepts some "Message", makes it
into a concrete class and dispatches it to the overloaded handler function:

// A, B, C, ... derived from some Base

template<class HandlerT>
void dispatchMsg(HandlerT& h, Msg m)
{
        if(m.getName()=="A")
        {
                h.onMsg(A(m));
        }else
        if(m.getName()=="B")
        {
                h.onMsg(B(m));
        }
// etc
}

the handler class has to implement overloaded handler functions for the the
classes it is interested in and (right now) a 'catch-all' handler for the
Base& (to insure that the thing compiles). Ideally I would like to eliminate
this requirement by detecting whether HandlerT has a onMsg(T&) and providing
a no-op for that (via another level of indirection), some thing like:

template<class HandlerT>
void dispatchMsg(HandlerT& h, Msg m)
{
        if(m.getName()=="A")
        {
                dispatcher<HAS_METH(h, void, onMsg, A&)>::dispatch(A(m));
        }else
        if(m.getName()=="B")
        {
                dispatcher<HAS_METH(h, void, onMsg, B&)>::dispatch(A(m));
        }
// etc
}
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