ios - 在 Swift 中删除/排除枚举案例

Question

这是一个包含游戏中启用的操作的结构:

struct OperationsEnabled {
    var addition = 1
    var subtraction = 0 // disabled
    var multiplication = 1
    var division = 1
}

这是我用来生成简单算术题的枚举:

enum BinaryOperation: String {
    case Addition = "+"
    case Subtraction = "-"
    case Multiplication = "×"
    case Division = "÷"

    func rangesForDifficulty(difficulty: Difficulty) -> (Range<Int>, Range<Int>) {
        switch self {
        case .Addition:
            switch difficulty {
            case .Easy: return (1...10, 1...10)
            case .Intermediate: return (10...100, 1...100)
            case .Difficult: return (109...999, 109...999)
            }
        case .Subtraction:
            switch difficulty {
            case .Easy: return (1...10, 1...10)
            case .Intermediate: return (10...100, 1...100)
            case .Difficult:  return (109...999, 109...999)
            }
        case .Multiplication:
            switch difficulty {
            case .Easy: return (1...10, 2...4)
            case .Intermediate: return (1...50, 3...7)
            case .Difficult: return (10...100, 4...15)
            }
        case .Division:
            switch difficulty {
            case .Easy: return (1...10, 2...4)
            case .Intermediate: return (1...50, 3...7)
            case .Difficult: return (10...100, 4...15)
            }
        }
    }

    func apply(number1: Int, _ number2: Int) -> Int {
        switch self {
        case .Addition:
            return number1 + number2
        case .Subtraction:
            return number1 - number2
        case .Multiplication:
            return number1 * number2
        case .Division:
            return number1 / number2
        }
    }
}

// Let's make a new question
func newQuestion() {
    let (range1, range2) = binaryOperation.rangesForDifficulty(difficulty)
    let number1 = Int.random(range1)
    let number2 = Int.random(range2)
    let answer = binaryOperation.apply(number1, number2)
}

我想过滤掉操作。例如，我需要排除游戏中不允许的操作，但这里似乎没有办法使用条件语句。我该怎么做？

Answer 1

您想从可用操作中随机选择一个操作。为采用 OperationsEnabled 的 BinaryOperation 创建一个初始化程序并创建一个 BinaryOperation。

init?(enabled: OperationsEnabled) {
    let all: [(BinaryOperation, Int)] = [(.Addition, enabled.addition), (.Subtraction, enabled.subtraction),
             (.Multiplication, enabled.multiplication), (.Division, enabled.division)]
    let avail = all.flatMap { (op, on) in on == 1 ? op : nil }
    if avail.isEmpty {
        return nil
    }
    else {
        let index = Int(arc4random_uniform(UInt32(avail.count)))
        self = avail[index]
    }
}

用法:

let enabled = OperationsEnabled(addition: 1, subtraction: 1, multiplication: 0, division: 0)
let binaryOperation = BinaryOperation(enabled: enabled)!    

注意事项:

1. 其工作原理是首先创建一个元组配对列表，其中包含与其可用性配对的操作。
2. flatMap 用于仅选择可用的操作。
3. 如果没有任何操作被标记为可用，则 avail 将为空并且此 failable 初始化程序将返回 nil。
4. 操作是从可用操作列表中随机选择的。