Question

I am making a template class with an inner utility class. All specializations of the template want the same inner class:

template<...> class Outer {
    class Inner { };
};

That gives me Outer<...>::Inner but I want all Inner to be the same type, as if I’d just written:

class Inner { };
template <...> class Outer { };

or if Outer were simply not a template class:

class Outer {
    class Inner { };
};

giving me Outer::Inner. I’d like to have Outer::Inner work for all Outer<> if that’s possible (just for namespace/clarity reasons). Otherwise of course I can just move Inner out.

Answer 1

The nested class can be a non-template, but every instantiation of the template will have its own nested class because they’re (otherwise) unrelated types. You can do

namespace detail {

class Inner {};

} // detail

template<...>
class Outer {
    typedef detail::Inner Inner;
};