如何在swift中不使用类型转换从不同的类访问相同的propety

Question

I have 2 class which have same number of properties with same name. I want to access property without type casting.

class A : NSObject {
    var amount : Int = 10
}

class B : NSObject {
    var amount : Int = 20
}

Now I want to double the value of amount property like this

main() {
    let classA : A()
    print(doubleValue(classA))

    let classB : B()
    print(doubleValue(classB))
}

func doubleValue(myClass:AnyObject) -> Int {
    return myClass.amount * 2
}

Please suggest how can I achieve this.

Answer 1

This is exactly what protocol are used for. Let us call this new protocol Amountable and add the amount property.

protocol Amountable {
    var amount: Int { get set }
}

If you want to provide a default implementation for doubleValue() you can event use protocol extension as follows:

extension Amountable {
    mutating func doubleValue() {
        self.amount *= 2
    }
}

Finally, let your classes conform to the protocol:

class ClassA: Amountable {
    // Implementation of classA here
}

class ClassB: Amountable {
    // Implementation of classB here
}

objectA = ClassA()
objectA.doubleValue()