AMDG On 05/31/2017 03:25 AM, Joaquin M López Muñoz via Boost-users wrote:

Say I have an object a of type

any>,_self&>

and an object b of type

any

where Concept1 is a subconcept of Concept2. Is it possible to make a refer to b rather than the object wrapped by b? I mean:

any_cast(&a)==&b typeid_of(a)==typeid(b)

A solution involving wrapping/copying b into some auxiliary entity would be acceptable too. This questin is obviously connected to the implementation of boost::any_collection, as Steven will undoubtedly have guessed.

You can do this using the (internal, undocumented) constructor any(detail::storage, const binding&); which effectively lets you pass a void* and and and vtable. With the public API, you need an auxiliary concept like this: #include #include #include #include #include #include <iostream> using namespace boost::type_erasure; namespace mpl = boost::mpl; typedef mpl::vector, ostreamable<> > test_concept; template struct make_reference { static P& apply(T& t) { return t; } }; int main() { any x(42); using extra_concept = mpl::vector > >; binding b1 = make_binding > > >(); binding > > b2 = make_binding > > >(); any >, _self&> ref( call(b1, make_reference<_self, any >(), x), b2); std::cout << ref << std::endl; } In Christ, Steven Watanabe