Simple way to reference member variables of base class templates

user_4306274 0
Viewed 360

Is there any way to reference member variables of base class templates without base class names and scope resolution operator?

template<typename D>
struct B0 {
    int value;
};
struct D0: B0<D0> {
    D0() {
        B0<D0>::value = 1; // OK.
        value = 1;         // OK without `B0<D0>::`.
    }
};

template<typename T>
struct B1 {
    T value;
};
template<typename T>
struct D1: B1<T> {
    D1() {
        B1<T>::value = 1; // OK.
        // value = 1; // Compile error without `B1<T>::`.
                      // Compile error: use of undeclared identifier 'value'
                      // `B1<T>::` is tedious everywhere `value` is referenced.
    }
};

template<typename T, typename D>
struct B2 {
    T value;
};
template<typename T>
struct D2: B2<T, D2<T>> { // CRTP
    D2() {
        B2<T, D2<T>>::value = 1; // OK.
        // value = 1; // Compile error without `B2<T, D2<T>>::`.
                      // Compile error: use of undeclared identifier 'value'
                      // `B2<T, D2<T>>::` is more tedious for CRTP.
    }
};

int main() {
    return 0;
}

Is it possible to not write B1<T>:: or B2<T, D2<T>>:: which is tedious everywhere value is referenced?

class-template base-class name-lookup templates c++
1 Answers

As the solutions, you have to make the name value dependent to make it visible for name lookup. Besides the one you've showed, you can also:

  1. Use using to introduce the name,

    template<typename T>
struct D1: B1<T> {
    using B1<T>::value;   // or move it in method's scope according to your intent
    D1() {
        value = 1;        // OK.
    }
};

  2. Qualify with this->.

    template<typename T>
struct D1: B1<T> {
    D1() {
        this->value = 1;  // OK.
    }
};
user_33097900
Related