enum SomeEnum {
    ns_empty, ns_decltype
};

template <SomeEnum ns>
class SomeClass;

class Base {
protected:
    void myfun();
};

template <>
class SomeClass<ns_empty> : public Base {
    typedef SomeClass<ns_decltype> type; // navigation jumps to enclosing class
    
    void foo(void *p) {
        static_cast<SomeClass*>(p)->myfun(); // myfun is unresolved
    }
};


template <>
class SomeClass<ns_decltype> : public Base {
    typedef SomeClass<ns_empty> type; // navigation jumps to enclosing class
    
    void foo(void *p) {
        static_cast<SomeClass*>(p)->myfun(); // here it is resolved
    }
};