Stefan Seefeld wrote:
As I understand your request, you want to roll your own switch statement, but with more expressive values than simple numbers. In other words, you want a mapping from types to variant type discriminators:
variant<A, B, C> v = ....; switch (v.which()) { case v::type_id<A>::value: break; case v::type_id<B>::value: break; }
It seems you completely misunderstood. I absolutely do not want to do such a thing. As I already said, what I want to do has no relation with variant. Variant is just an example of a library that does static visitation, and that uses its own type identification mechanism instead of the one bundled with C++. What I want to do, is to provide visitation on top of the native C++ RTTI feature, with "naked" and unmodified polymorphic variables (which are not in a variant or anything else that maintains its own additional type identifier). As the example I wrote demonstrated, as the title of the thread clearly states, etc. The switch was no example of interface: it was an example of how visitation could be *implemented*. Indeed, since RTTI is broken (it is not a constant expression), such tricks are necessary to make things work. The example of interface was after that. Basically, providing an variant-like interface for polymorphic objects that have already decayed.
Certainly. But I haven't seen any good example on *what* I may want to compute on a string at compile-time. To me...
This thread just provided one possible good reason to do so.