Swift 函数输入通用同时符合 Class 和协议

Question

我正在尝试让一个函数采用符合 class 和协议的通用输入，以便处理一些属于 class 而另一些属于 class 的值代表。它适用于单个类型，但不适用于类型数组（符合 super class 和委托）。相反，编译器抛出错误“实例方法 'printValues(for:)' 要求 'MeasurementClass' 符合 'UnitDelegate'”

我添加了下面的代码，这会更有意义。只需将它放在 Swift Playground 中即可。如果你运行按原样，你可以看到它正确地打印了用户的距离和步数。如果您取消最后几行的注释，则无法对数组使用相同的函数。

我的目标是能够传递符合 UnitDelegate 和 MeasurementClass（又名 MeasurementObject 类型别名）的类型数组并处理值。我想要一个数组，因为我需要一堆符合 MeasurementObject 的不同 classes。

protocol UnitDelegate: class{
    var units: [String: String] { get }
}

class MeasurementClass{
    var imperial: Double!
    var metric: Double!
    
    convenience init(imperial: Double, metric: Double){
        self.init()
        self.imperial = imperial
        self.metric = metric
    }
}

typealias MeasurementObject = MeasurementClass & UnitDelegate


class Distance: MeasurementObject{
    var units = ["imperial": "miles", "metric":"kms"]
}

class Steps: MeasurementObject{
    var units = ["imperial": "steps", "metric":"steps"]
}

class User{
    func printValues<T: MeasurementObject>(for type: T) {
        print("\(type.imperial!) \(type.units["imperial"]!) = \(type.metric!) \(type.units["metric"]!)")
    }
}

//This is what I'm trying to achieve in the for loop below
let distance = Distance(imperial: 30, metric: 48.28)
let steps    = Steps(imperial: 30, metric: 30)
let user     = User()
user.printValues(for: distance)
user.printValues(for: steps)


//let types = [distance, steps]
//
//for type in types{
//    user.printValues(for: type)
//}

Answer 1

不是您问题的直接答案，但您只需要添加一个枚举以将测量类型存储到您的 class，并将计算的属性存储到 return对应的词典。不需要使用协议，协议组合，class and/or subclass 来完成你想做的事情：

struct AMeasurement {
    let imperial: Double
    let metric: Double
    let kind: Kind
    enum Kind { case distance, steps }
    var units: [String: String] {
        switch kind {
        case .distance: return ["imperial": "miles", "metric":"kms"]
        case .steps: return ["imperial": "steps", "metric":"steps"]
        }
    }
}

extension AMeasurement {
    func printValues() {
        print("\(imperial) \(units["imperial"]!) = \(metric) \(units["metric"]!)")
    }
}

let distance = AMeasurement(imperial: 30, metric: 48.28, kind: .distance)
let steps = AMeasurement(imperial: 30, metric: 30, kind: .steps)
let types = [distance, steps]

for type in types {
    type.printValues()
}

30.0 miles = 48.28 kms
30.0 steps = 30.0 steps

Swift 函数输入通用同时符合 Class 和协议

Swift Function Input Generic Conform To Both Class And Protocol

generics

delegates

protocols

swift