Swift: overriding typealias inside subclass

Question

So I was thinking about a custom pattern in my project, but I can\'t get it to work. The main idea is to change the typealias on every subclass to get access to the

Answer 1

Unfortunately there is no good workaround for this problem.

The main idea to override the typealias would work in this case but consider the following:

protocol TakeAndGet {
    typealias T
    func take(value: T)
    func get() -> T
}

class FirstClass: TakeAndGet {
    typealias T = FirstClass

    var property = 0

    func take(value: T) {
        value.property = 4
    }

    func get() -> T {
        return FirstClass()
    }
}

class SecondClass: FirstClass {

    typealias T = SecondClass

    var property2 = "hello"
}

If the typealias of the SecondClass overrides the other one the take method would work since it takes a subclass which can be treated as the superclass. But the get method cannot implicitly convert FirstClass to SecondClass. Therefore it is not possible to override a typealias.

Now if we want to override the get function with get() -> SecondClass it wouldn't work since it has not the same signature as the one in the superclass. In addition we inherit the get method which results in an ambiguous use:

SecondClass().get() // which type gets returned? SecondClass or FirstClass

So you have to try a different approach.