Class UniqueInt

oneflow/maybe/just_test.cpp:226–241

TEST(Just, WithMsg) {
  struct UniqueInt {
    int x;

    void drop() { x = -333; }

    explicit UniqueInt(int x) : x{x} {}
    UniqueInt(const UniqueInt& i) = delete;
    UniqueInt(UniqueInt&& i) noexcept : x{i.x} { i.drop(); }  // NOLINT
    UniqueInt& operator=(const UniqueInt& i) = delete;
    UniqueInt& operator=(UniqueInt&& i) noexcept {
      x = i.x;
      i.drop();
      return *this;
    }
    ~UniqueInt() { drop(); }
  };

  using Error = simple::StackedError<std::string>;
  using MaybeInt = Maybe<UniqueInt, Error>;