面向协议的编程和类 Swift

Question

I am trying to implement protocol oriented class watching tutorials from on of the popular tutorial sites. I got everything correct so far but for some reason one of the properties is not being updated while the others are updated. Here is the code :

protocol Paintable  : class {
    var primaryBodyColor : String{get set}
    var secondaryBodyColor : [String]? {get set}

    func paint(newPrimaryColor : String, newSecondaryColor : [String]?)
}


extension Paintable   {
    var primaryBodyColor : String {
        get {
            return "Black"
        }
        set {
        }
    }
}

protocol Wheeled {
    var numberOfWheels : Int {get set}
}


extension Wheeled {
    var numberOfWheels : Int {
        get {
            return 4
        }

        set {
        }
    }
}
protocol EngineSize {
    var engineSizeCC : Int {get set}
}

extension EngineSize {
    var engineSizeCC : Int {
        return 2300
    }
}




class Honda : Transport, Paintable, Wheeled, EngineSize {
    var secondaryBodyColor : [String]?
    var engineSizeCC : Int
    //We can also override default initializer of protocol, here we are going to instantiate with our initializer
    init(engineSizeCC : Int){
        self.engineSizeCC = engineSizeCC
    }

    func paint(newPrimaryColor: String, newSecondaryColor: [String]?) {
        primaryBodyColor = newPrimaryColor
        secondaryBodyColor = newSecondaryColor
    }
}

var civic = Honda(engineSizeCC: 400)
civic.primaryBodyColor
civic.passengerCapacity
civic.numberOfWheels
civic.engineSizeCC

civic.paint("blue", newSecondaryColor: ["Red","Purple"])
civic.primaryBodyColor -> "Black"
civic.secondaryColor -> ["Red"], ["Purple"] 

The problem I am having is the primaryBodyColor stays "Black" even though I called the "paint" function to set the primary color as "Blue" and secondary color.

I am new to protocol oreinted programming so I will appreciate help on resolving this issue.

Answer 1

Extensions cannot store properties, which is perhaps why you don't have any code in the setter of primaryBodyColor . The implementation of primaryBodyColor needs to be in a struct/class, just as you've done with seondaryBodyColor . So if just before that line within the Honda class you include the following line, your code will work as expected...

var primaryBodyColor = "black"

Answer 2

Like it's been said in the comments, your implementation of the primaryBodyColor always return black and doesn't allow to be set.

By default, properties in Swift have a get and set method, there's no need to add {get set} after each one of them.

If you want to add a default value, you can do it like this:

var primaryBodyColor = "Black"

You don't even need to declare it as String because the compiler will realize that "Black" is a string and type it correctly.