Swift 在子协议中用具体类型替换关联类型

Question

protocol A {
    associatedtype T
    var t: T { get }
}

protocol B: A where T == Int {}

var b: B? = nil     //  Protocol 'B' can only be used as a generic constraint
                    //  because it has Self or associated type requirements.
                    

Is there a way to create an extended protocol (B) that assigns a concrete type to the base protocol's (A's) associated type, and by doing so "removes" the associated type requirements, and becomes a protocol with no associated types, usable not only as a generic constraint?

Answer 1

No, it doesn't seem to work so the associated type always stays inside

protocol A {
    associatedtype T
    var t: T { get }
}

protocol B: A {
    override associatedtype T = Int
}

There are methods to overcome this, for example wrapped classes

 class WrappedB: B {
    var t: Int
    
    init<S: B>(_ object: S) where S.T == Int {
        self.t = object.t
    }
}

var b: WrappedB = WrappedB(BB())