Protocol variable implementing another protocol

问题

I'm trying to do something like that, but then, ParentC doesn't conform to Parent because its children member isn't Child but ChildC

Which is weird because ChildC implements Child...

Is this a limit of Swift? Or is there is a way of doing that?

(I do not ask for an alternative solution, I want to know if this is possible)

protocol Parent: Codable {
    var children: [Child] { get }
}

protocol Child: Codable {
    var name: String { get }
}

struct ParentC: Parent {
    var children: [ChildC]
}

struct ChildC: Child {
    var name: String
}

回答1:

You can workaround this variance "limitation" by making Parent a protocol with associated type:

protocol Parent: Codable {
    associatedtype ChildType: Child
    var children: [ChildType] { get }
}

This will impact the places you can use Parent though, since protocols with associated types have some restrictions on where to use them.

来源：https://stackoverflow.com/questions/49554288/protocol-variable-implementing-another-protocol