maybe.cpp

template <class T>
struct Maybe {
 public:
  Maybe() {}
  explicit Maybe(T v) : state_(v) {}

  bool isJust() {
    return state_;
  }

  T get() {
    assert state_;
    return *state_;
  }

  T fromMaybe(const T& d) {
    if (state_) {
      return *state_;
    } else {
      return d;
    }
  }

 private:
  unique_ptr<T> state_;
};