在 Swift 中将实例变量的属性保存到 Struct 的静态变量数组中

Posted 2023-05-07

【中文标题】在 Swift 中将实例变量的属性保存到 Struct 的静态变量数组中

【英文标题】：Saving Properties of an Instance Variable to a Struct's Static Variable Array in Swift

【发布时间】：2018-04-28 08:10:54

【问题描述】：

我不确定我是否正确执行此操作，我正在尝试将 Struc 的实例保存到静态变量数组中，但实例的名称并未添加到数组中...这是下面的代码：

struct SwimmingWorkout 
    let distance: Double //meters
    let time: Double //Seconds
    let stroke: Stroke

    enum Stroke 
        case freestyle, butterfly, backstroke, breaststroke
    

    static var freestyleWorkouts = [SwimmingWorkout]()
    static var butterflyWorkouts = [SwimmingWorkout]()
    static var backstrokeWorkouts = [SwimmingWorkout]()
    static var breaststrokeWorkouts = [SwimmingWorkout]()

    func save() 
        switch stroke 
        case .freestyle:
            SwimmingWorkout.freestyleWorkouts += [self]
        case .butterfly:
            SwimmingWorkout.butterflyWorkouts += [self]
        case .backstroke:
            SwimmingWorkout.backstrokeWorkouts += [self]
        case .breaststroke:
            SwimmingWorkout.breaststrokeWorkouts += [self]
        default:
            print("Error")
        
    

我期待

let swim1 = SwimmingWorkout(distance: 100, time: 180, stroke: .butterfly)
let swim2 = SwimmingWorkout(distance: 200, time: 320, stroke: .butterfly)

swim1.save()
swim2.save()

for workout in SwimmingWorkout.butterflyWorkouts 
    print(workout)

应该会产生输出：

swim1(distance: 100.0, time: 180.0, stroke: Stroke.butterfly)
swim2(distance: 200.0, time: 320.0, stroke: Stroke.butterfly)

但我明白了：

SwimmingWorkout(distance: 100.0, time: 180.0, stroke: __lldb_expr_18.SwimmingWorkout.Stroke.butterfly)
SwimmingWorkout(distance: 200.0, time: 320.0, stroke: __lldb_expr_18.SwimmingWorkout.Stroke.butterfly)

我在这里缺少什么？我什至不完全确定为什么stroke: __lldb_expr_18.SwimmingWorkout.Stroke.butterfly 与我的预期结果相比会出现这种情况。

先谢谢了，供参考，提示如下：

向 SwimmingWorkout 添加一个名为 save() 的实例方法，该方法不接受参数并且没有返回值。此方法会将其实例添加到 SwimmingWorkout 上与其游泳行程相对应的静态数组中。在 save() 内部编写一个 switch 语句来打开实例的 stroke 属性，并将 self 附加到正确的数组中。对您在上面创建的两个 SwimmingWorkout 实例调用 save，然后打印应该添加它们的数组以查看您的 save 方法是否正常工作。

【参考方案1】：

您需要实现CustomStringConvertible 并实现description 属性以返回SwimmingWorkout 结构的字符串表示形式。

此外，由于您的预期输出将一个数字与每次游泳相关联（swim1、swim2），您可能也应该添加一个 id 属性。

这是你更正后的 SwimmingWorkout 结构：

struct SwimmingWorkout: CustomStringConvertible 
    let distance: Double //meters
    let time: Double //Seconds
    let stroke: Stroke

    static var nextID = 1
    let id: Int

    init(distance: Double, time: Double, stroke: Stroke) 
        self.distance = distance
        self.time = time
        self.stroke = stroke
        self.id = SwimmingWorkout.nextID
        SwimmingWorkout.nextID += 1
    

    enum Stroke 
        case freestyle, butterfly, backstroke, breaststroke
    

    static var freestyleWorkouts = [SwimmingWorkout]()
    static var butterflyWorkouts = [SwimmingWorkout]()
    static var backstrokeWorkouts = [SwimmingWorkout]()
    static var breaststrokeWorkouts = [SwimmingWorkout]()

    func save() 
        switch stroke 
        case .freestyle:
            SwimmingWorkout.freestyleWorkouts += [self]
        case .butterfly:
            SwimmingWorkout.butterflyWorkouts += [self]
        case .backstroke:
            SwimmingWorkout.backstrokeWorkouts += [self]
        case .breaststroke:
            SwimmingWorkout.breaststrokeWorkouts += [self]
        
    

    var description: String 
        return "swim\(id)(distance: \(distance), time: \(time), stroke: Stroke.\(stroke))"
    

【参考方案2】：

删除

enum Stroke 
        case freestyle, butterfly, backstroke, breaststroke
    

来自struct SwimmingWorkout 并将其写出“结构”，您的代码应该是正确的。