When is using 'typeid' the best solution?

Question

There are many reasons not to use typeid. Other than for using members of type_info (implementation defined behavior), it is usually (always?) possible to provide similar functionality using other C++ language features, eg: overloading, virtual functions etc.

So, excluding usage that relies on the implementation defined behavior, does anybody have a real world example where typeid is the best solution?

Answer 1

boost::any uses typeid to implement any_cast.

template<typename T> any_cast(const any& other) {
   if(typeid(T) != other.type()) throw bad_any_cast();

   //...actual cast here...
}

You can't be sure T is polymorphic, so dynamic_cast is out of the question, and the enclosed type within the boost::any call is lost by now, so none of the other casts can provide any sort of type safety.