Question

In this piece of code taken from http://drdobbs.com/cpp/184403774:

template <class L, class R>
class MinResult {
    L& lhs_;
    R& rhs_;
public:
    operator L&() { return lhs_ < rhs_ ? lhs_ : rhs_; }   // <----
    operator R&() { return lhs_ < rhs_ ? lhs_ : rhs_; }   // <----
    MinResult(L& lhs, R& rhs) : lhs_(lhs), rhs_(rhs) {}
};

What is the code above trying to do at lines pointed by arrows?

I am a beginner in C++ and I understand that we can override / define operator() by defining it.

But then shouldn’t it be defined like this

L& operator() { return lhs_ < rhs_ ? lhs_ : rhs_; }

I am sure this is some differenct syntax since operator() is supposed to be one word. Also, you cannot define two of them with different return types.

Answer 1

No this is type cast operator.

You can define

operator type() const

As operator that allows to cast to the type. For example

class date {
public:
   operator time_t() const; // convert to time_t
};

The operator() has a different purpose, it allows to use the class as “function” and this is not the case here