I have a class that inherits from 2 sets of base classes, according to variadic template arguments. One of those sets defines a virtual function. I want to do something like this but I’m not sure how it could compile:

template <class T>
struct Base {
    void virtual foo(T t) = 0;
};

template <class T>
struct Holder {
    T t;
};

template <class... T>
struct Child : Base<T>..., Holder<T>... {
    template <class O>
    void Base<O>::foo(O t) override {  // << this won't compile
        Holder<O>::t = t;
    }
};

LIVE

It gives the following error:

error: invalid use of incomplete type ‘struct Base’