associatedtype 协议一致性问题

Question

I have 3 protocols to define a relationship where a Mediator uses Host to extract Client

1. Host
2. Client
3. Mediator

My goal is to have Host also act as a Mediator . These are my class and protocol definitions:

class Host {}
class Client {}

protocol HostProtocol {}
protocol ClientProtocol {}

extension Host: HostProtocol {}
extension Client: ClientProtocol {}

protocol MediatorProtocol {
    associatedtype H = HostProtocol
    associatedtype C = ClientProtocol

    func getClientFrom(host: H) -> C?
}

I then extend my MediatorProtocol to add an implementation

extension MediatorProtocol where H == Host, C == Client {
    func getClientFrom(host: H) -> C? {
        return Client()
    }
}

Now when I try to make my Host conform to MediatorProtocol, I get an error saying

Type 'Host' does not conform to protocol MediatorProtocol

extension Host: MediatorProtocol {}

Any ideas?

Answer 1

Just change protocol specification on this

extension MediatorProtocol where H == Host, C == Client {
    func getClientFrom(host: Host) -> Client? {
        return Client()
    }
}

You can rewrite it even without where spec. Swift can infer associated types from function declaration (that's why it couldn't do so with your code).

extension MediatorProtocol {
    func getClientFrom(host: Host) -> Client? {
        return Client()
    }
}