Bowling Game: State Machine: Std::Variant: Step 18

Making the “all spares” test pass means adding some logic to the WaitingForSecondRollWith1Bonus class:

        class WaitingForSecondRollWith0Bonuses
        {
            int first;
            int sumOfRolls(int pins) const { return first + pins; }
        public:
            WaitingForSecondRollWith0Bonuses(int first) : first(first) {}
            State Update(int pins, int& score, int& frame) const
            {
                if (sumOfRolls(pins) > 10)
                    throw std::invalid_argument("sum of rolls in a frame must be <= 10");
                score += pins;
                ++frame;
                if ((frame == 10) && (sumOfRolls(pins) == 10))  return LastFrameWith1Bonus{};
                if (frame >= 10)                                return GameOver{};
                if (sumOfRolls(pins) == 10)                     return WaitingForFirstRollWith1Bonus{};
                                                                return WaitingForFirstRollWith0Bonuses {};
            }
        };
  ...
        struct LastFrameWith1Bonus
        {
            State Update(int pins, int& score, int& /*frame*/) const
            {
                score += pins;
                return GameOver{};
            }
        };

If we rolled a spare in the last frame, we still have 1 roll to go, so we check to see if we’re in frame 10 now and if it’s a spare, and if both those are true, we go to a special LastFrameWith1Bonus state, which simply sums in the pins of the next roll and ends the game.

I see a little refactoring opportunity, though: two instances of (sumOfRolls(pins) == 10). Let’s refactor that and then click next.