2. Is it possible to convert between "any" instances with different concept sets or value types? For instance, are these possible? any< mpl::vector< addable<>, incrementable<>, decrementable<> >
a;
any< mpl::vector< addable<> >
b = a;
I find this an interesting question. I use the review to change a private but real project and replace all of my OO-style interfaces by TypeErasure. I got the following to compile and work (you need copy_constructible): typedef any< boost::mpl::vector< boost::type_erasure::typeid_<>, boost::type_erasure::copy_constructible<>, boost::type_erasure::addable<>, boost::type_erasure::incrementable<>, boost::type_erasure::decrementable<> > > AnyA; typedef any< boost::mpl::vector< boost::type_erasure::copy_constructible<>, boost::type_erasure::typeid_<>, boost::type_erasure::addable<> > > AnyB; AnyA a(10); AnyB b = a; OTOH, this does not compile: AnyB b2(10); AnyA a2=b2; Which brings me to the following use case. Supposing I have 3 classes IA <- IB <- IC and 1 object of each held as shared_ptr, I can dynamic_pointer_cast from one to another. But if I have 3 any's of concepts A,B,C, B containing A's concepts + some more, and C containing B's concepts + some more, I can "upcast" as shown above from C to B and B to A, but not the other way around, right? Even if I have an object fulfilling A,B and C. Thanks, Christophe PS: so far I got only one warning: check_match does not use its parameter op.