Swift中具有关联类型的协议的问题

Question

I have one framework ProviderFramework with the following contents:

public class Provider {

    public func fun(some: Model) {

    }

}

public class Model {

    public let id: Int

    init(id: Int) {
        self.id = id
    }

}

and another UserFramework with the following contents:

public protocol ProviderProtocol {

    func fun(some: ModelProtocol)

}

public protocol ModelProtocol {

    var id: Int {get}

}

What I want is to make the Provider class conform to the ProviderProtocol class. So in a framework that imports both of the previously mentioned frameworks I have this:

extension ProviderFramework.Model: UserFramework.ModelProtocol {}
extension ProviderFramework.Provider: UserFramework.ProviderProtocol {}

Unfortunately, this results in an error for the second conformance. So, I tried using an associated types and my ProviderProtocol turned into this:

public protocol ProviderProtocol {

    associatedtype T: ModelProtocol

    func fun(some: T)

}

and the problematic conformance to this:

extension ProviderFramework.Provider: UserFramework.ProviderProtocol {
    public typealias T = ProviderFramework.Model
}

Now there aren't any compile errors, but if I want to use the Protocol as a type like this:

class Consumer {

    var provider: ProviderProtocol?

}

I again get an error: 'Protocol 'ProviderProtocol' can only be used as a generic constraint because it has Self or associated type requirements'

I would want to be able to do the last thing. Do I have some bug in my code or if not is there some alternative solution for this problem?

Thanks a lot in advance.

Answer 1

According to the second approach, why not use Provider instead of ProviderProtocol? Since you confirmed typealias T as ProviderFramework.Model in the extension of class Provider .

class Consumer {
    var provider: Provider?
}