derived.cpp

using namespace winrt;
using namespace Windows::Foundation;

struct Base: implements<Base, composable, IStringable>
{
    static IInspectable CreateInstance(IInspectable const& base, IInspectable& inner)
    {
        return impl::composable_factory<Base>::CreateInstance<IInspectable>(base, inner);
    }

    hstring ToString()
    {
        return L"base";
    }
};

struct Derived : implements<Derived, composable, composing, IClosable>
{
    Derived()
    {
        Base::CreateInstance(*this, m_inner);
    }

    void Close() {}
};

int main()
{
    IInspectable derived = make<Derived>();
    derived.as<IClosable>().Close(); // outer query
    derived.as<IStringable>().ToString(); // inner query
}