CODEWITHSUNDEEP
c++templatesinheritance
N F
N F

Reputation: 37

Operator overloading and inheritance (keeping the same type)

I have a bit of a problem with operator overloading and inheritance in C++.

Quick sketch:

class A {
public: 
    A operator+ (const A &b) const { ... }
};

class B : public A {
    ...
};

Now suppose I have two instances of B, x and y. If I add them I will get a thing of type A, however I want it to be of type B.

What is the best way of accomplishing this (aside from reimplementing them in class B) ? CRTP?

Upvotes: 0

Views: 124

Answers (1)

bfair
bfair

Reputation: 1111

You can implement operator+ outside of the class as a template:

template<class type> type operator+(const type& left, const type& right)
{
    type toReturn;
    toReturn.value = left.value + right.value;
    return toReturn;
}

class A {
private:
    int value;

    template <class type> 
    friend type operator+<type>(const type& left, const type& right);
};

class B : public A {
};

int main()
{
    B test1, test2;

    B test3 = test1 + test2;
}

This approach has certain down-sides. The compiler will aggressively try to instantiate the operator+ template for types which you don't want to define operator+, so be aware of that.

Upvotes: 1

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