Re: double dispatch, half compile-time
One solution would probably be to use External Polymorphism, like:
Adapter<Variant, long> av(v);
I<long> *iV = &av;
Adapter<Value<int>, long> aval(val);
I<long> *iVal = &aval;
Right here you have assumed simultaneous explicit knowledge at compile
time of both int (Value<int>) and long (A == long). Once you have this,
the solution is easy (as you have shown). The problem is that I don't
have that. I know A at compile time, but I only know T up to abstract
template <class A> void single_bound(A& a, const Variant& v)
// what can I do here to turn v into Adapter<A,Value<T> > ?
So unfortunately, your suggestion might be useful when you know A at the
time of the creation of the Variant, but not when A is supplied elsewhere.
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