Swift中以泛型數組作為參數的函數

Question

我想做一個將泛型數組作為參數的泛型函數。 我有兩個類Animal和Bird以及兩個協議Animals＆Birds，並且我的方法參數符合這兩個協議，但是我無法添加到數組中。

protocol Birds {
    var canFly: Bool {get set}
}

protocol Animals {
    var name: String {get set}
    var legs: Int {get set}
}

class Animal: Animals {
    var name: String
    var legs: Int

    init(name: String, legs: Int) {
        self.name = name
        self.legs = legs
    }
}

class Bird: Birds {
    var canFly: Bool
    init(canFly: Bool) {
        self.canFly = canFly
    }
}

func myTestGenericMethod<T>(array: [T]) where T: Animals & Birds {
    for (index, _) in array.enumerated() {
        print("At last i am able to get both Animal and Bird")
    }
}

let cat = Animal(name: "cat", legs: 4)
let dog = Animal(name: "dog", legs: 4)
let crow = Bird(canFly: true)
myTestGenericMethod(array: [dog])

myTestGenericMethod(array: [cat, dog]) // Not Able to add this to array

Answer 1

當您where T: Animals & Birds寫where T: Animals & Birds ，必須從Animals 與 Birds擴展T

但是cat與dog是不是來自延長Animals 和 Birds 。 所以這是問題。

據我了解，您希望T必須從Animals 或 Birds擴展。 要做到這一點，我們必須有一個擴展了Animals和Birds的基本協議。 更改一些代碼並修復它。

@objc protocol Base {
}

protocol Birds : Base {
  var canFly: Bool {get set}
}

protocol Animals : Base {
  var name: String {get set}
  var legs: Int {get set}
}

class Animal: Animals {
  var name: String
  var legs: Int

  init(name: String, legs: Int) {
    self.name = name
    self.legs = legs
  }
}

class Bird: Birds {
    var canFly: Bool
    init(canFly: Bool) {
      self.canFly = canFly
    }
  }

func myTestGenericMethod<T: Base>(array: [T]) {
  for object in array {
    if object is Bird {
      let bird = object as! Bird
      print(bird.canFly)
    } else if object is Animal {
      let animal = object as! Animal
      print(animal.name)
    }
  }
}

let cat = Animal(name: "cat", legs: 4)
let dog = Animal(name: "dog", legs: 4)
let crow = Bird(canFly: true)
myTestGenericMethod(array: [crow, cat, dog] as! [Base])
myTestGenericMethod(array: [cat, dog])

Answer 2

在您的代碼中where T: Animals & Birds意味着您需要T為同時符合兩種協議的實例。 但是您沒有符合這兩種協議的類。 如果創建一個實例，則可以在通用方法中使用其實例。