C++ = operator

Suppose that objects A, B, and C are instances of class Foo. How should you design an assignment operator so that the "A=B=C;" statement would be allowed by a compiler but "(A=B)=C;" would not be allowed by a compiler?

Answer:

class Foo
{
    private:
        int a;
    public:
        const Foo& operator=(const Foo& other)
        {
            this->a = other.a;
            return *this;
        }
};

int main()
{
    Foo a,b,c;
    a = b = c;
    (a = b) = c;
}