Swift 继承的协议发送到函数作为 inout

Question

下面的代码无法编译。我正在尝试将 class 发送到更改 class 的函数，其中 class 符合协议。该协议继承自另一个基础协议。我希望编译器知道 s (SportsCar) 符合 Car 但它不符合。

如果函数 test_car 不更改参数 car，则此代码有效。

谢谢

protocol Car {
  var wheels: Int { get set }
}

protocol SportsCar : Car {
  var engine: Int { get set }
}


class Test {

    var p: Plunk
    var s: SportsCar

    init() {
        print("Making Test")
        p = Plunk()
        s = p
    }

    func run() {
        print("Running Test")
        test_car(car: s ) // error: argument type 'SportsCar' does not conform to expected type 'Car'
        print("Finished Test")
    }

    func test_car(car: inout Car) {
        print("Car has \(car.wheels) wheels")
        car.wheels += 1
        print("Wheel added")
        print("Car now has \(car.wheels) wheels\n")
    }

}


class Plunk : SportsCar {

    var wheels: Int
    var engine: Int
    var plunk: Bool

    init(){
        wheels = 4
        engine = 1
        plunk = true
    }

}

Answer 1

I am trying to send a class to a function

你应该告诉编译器：

protocol Car: AnyObject { ... }

所以现在编译器知道 Car 的符合者将是 class 的一个实例。所以您不再需要 inout 关键字：

func test_car(car: Car) { ... }

Swift 继承的协议发送到函数作为 inout

Swift inherited protocols sent to functions as inout

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