Why inheritance doesn’t work inside methods?

Question

This does not compile:

struct Base
{
    void something( int a ) { }
};
struct Derived : public Base
{
    static void something()
    {
        std::unique_ptr<Derived> pointer = std::make_unique<Derived>();
        pointer->something( 11 );
    }
};

It’s possible to fix with using Base::something but still, is it possible to make inheritance work as advertised even inside methods?

notice that the function in `Derived()` is `static` while the function in `Base` is not, so it doesn't override it. Also, even if the function in `Derived` were not static, the function in `Base` needs to be declared `virtual` to be overrriden — Gal, Jul 27 '21 at 13:26
I think the question is asking why `Base::something(int)` is not automatically accessible from `Derived:::something()`. — François Andrieux, Jul 27 '21 at 13:27

score 2 · Answer 1 · answered Jul 27 '21 at 13:28

By using the same name for the function in the derived class you hide the symbol from the base class.

You can solve it by pulling in the name from the base class with the using statement:

struct Derived : public Base
{
    // Also use the symbol something from the Base class
    using Base::something;

    static void something()
    {
        std::unique_ptr<Derived> pointer = std::make_unique<Derived>();
        pointer->something( 11 );
    }
};

score 0 · Answer 2 · answered Jul 27 '21 at 13:31

I'm not exactly sure what you are trying to accomplish. I added virtual, and changed the name of the Derived something class function, and put in two variants. One variant calls through virtual inheritance, the other calls Base class member function directly.

#include <iostream>

using std::cout;

namespace {

struct Base {
    virtual ~Base();
    virtual void something(int a) { std::cout << "Base a:" << a << "\n"; }
};

Base::~Base() = default;

struct Derived : Base {
    void something(int b) override { std::cout << "Derived b:" << b << "\n"; }
    static void action() {
        std::unique_ptr<Derived> pointer = std::make_unique<Derived>();
        pointer->something(11);
    }
    static void other_action() {
        std::unique_ptr<Derived> pointer = std::make_unique<Derived>();
        pointer->Base::something(11);
    }
};

} // anon

int main() {
    Derived::action();
    Derived::other_action();
}

Why inheritance doesn’t work inside methods?

2 Answers2