ذͨ͠ޙͷॲཧ࣍ͷ εςʔτΛฦ͚ͩ͢ func nextTurnState(from currentSide: Side) -> State { let nextSide = currentSide.flipped if board.validMoves(for: nextSide).isEmpty { if board.validMoves(for: currentSide).isEmpty { return .result(board.result()) } else { return .passing(side: nextSide) } } else { return .operating(side: nextSide, player: player(for: nextSide)) } }