Overloading comparison operators in derived class right private inheritance

I've got two classes here. A Base class:

class A
{
    int x;
public:
    A(int n):x(n){}

    friend bool operator==(const A& left, const A& right)
    {return left.x==right.x;}
};

and a derived class that inherits from A privately:

class B : private A
{
    int y;
public:
    B(int n,int x):A(x),y(n){}
    friend bool operator==(const B& left, const B& right)
    {
        i开发者_JS百科f(left.y==right.y)
        {/*do something here...*/}
        else{return false;}
    }
};

I know how to compare two instances of A: I just the member variables to each other. But how can I possibly compare instances of B? two instances could easily have different "x" members inside their associated "A" instances, but I have no idea how to compare those instances to each other.

You can cast the instances to A& and use the equality operator for class A:

if (static_cast<A&>(left) == static_cast<A&>(right)) {
    // ...
}