在不使用成员函数和友元函数的情况下实现运算符重载

Question

Is it possible for a non-member and non-friend function to achieve this?

Presume that it is a binary operator, which means we need to pass two arguments from different objects. How can it access the private members?

Answer 1

This is an example:

class Foo{
private:
    int m_i;
public:
    Foo(int i): m_i{i} {}
    int get() { return m_i; }
};

Foo operator+(Foo& foo1, Foo& foo2){
    return {foo1.get() + foo2.get()}; // you can not access m_i directly as you do in member functions and friend functions
}

Generally speaking, you use normal functions for operator overloading operators that don't modify the state left operand and don't need access to private or protected members directly.