Class Maybe

nan.h:242–293

template<typename T>
class Maybe {
 public:
  inline bool IsNothing() const { return !has_value_; }
  inline bool IsJust() const { return has_value_; }

  inline T ToChecked() const { return FromJust(); }
  inline void Check() const { FromJust(); }

  inline bool To(T* out) const {
    if (IsJust()) *out = value_;
    return IsJust();
  }

  inline T FromJust() const {
#if defined(V8_ENABLE_CHECKS)
    assert(IsJust() && "FromJust is Nothing");
#endif  // V8_ENABLE_CHECKS
    return value_;
  }

  inline T FromMaybe(const T& default_value) const {
    return has_value_ ? value_ : default_value;
  }

  inline bool operator==(const Maybe &other) const {
    return (IsJust() == other.IsJust()) &&
        (!IsJust() || FromJust() == other.FromJust());
  }

  inline bool operator!=(const Maybe &other) const {
    return !operator==(other);
  }

#if defined(V8_MAJOR_VERSION) && (V8_MAJOR_VERSION > 4 ||                      \
  (V8_MAJOR_VERSION == 4 && defined(V8_MINOR_VERSION) && V8_MINOR_VERSION >= 3))
  // Allow implicit conversions from v8::Maybe<T> to Nan::Maybe<T>.
  Maybe(const v8::Maybe<T>& that)  // NOLINT(runtime/explicit)
    : has_value_(that.IsJust())
    , value_(that.FromMaybe(T())) {}
#endif

 private:
  Maybe() : has_value_(false) {}
  explicit Maybe(const T& t) : has_value_(true), value_(t) {}
  bool has_value_;
  T value_;

  template<typename U>
  friend Maybe<U> Nothing();
  template<typename U>
  friend Maybe<U> Just(const U& u);
};

template<typename T>
inline Maybe<T> Nothing() {