duplicates:

• SR-55 non-@objc protocol existentials do not conform to their own protocol type

Issue Description:

I'm not sure if this is a bug or an expected behaviour, but for me this seems wrong.

I have a class with a generic type that needs to be an object. And I cannot use a protocol with an class type as type for this class.

class Holder<T: AnyObject> {
    var value: T? = nil
    
    init() {
        self.value = nil
    }
    
    init(_ value: T) {
        self.value = value
    }
}

protocol ObjectWithValue: class {
    var string: String { get }
}

class MyObject: ObjectWithValue {
    var string: String = "test"
}

let object = MyObject()
let holder1 = Holder(object)

let objectByProtocol: ObjectWithValue = object
let holder2 = Holder(objectByProtocol) // <- Error


let holder3 = Holder<ObjectWithValue>() // <- Error
holder2.value = object

With Xcode 10 Beta 6 I get following errors:

ClassType.playground:25:15: Cannot invoke initializer for type 'Holder<_>' with an argument list of type '(ObjectWithValue)'

ClassType.playground:27:15: 'Holder' requires that 'ObjectWithValue' be a class type