import Foundation

protocol Enabled {
    var isEnabled: Bool {get set}
}

class C: NSObject, Enabled {
    @objc dynamic var isEnabled: Bool = false
}

let c = C()

func observeMeDirectly(_ object: C) {
    let _ = object.observe(\.isEnabled, options: [.new]) { _, _ in
        print("changed")
    }
}

observeMeDirectly(c)
// this works fine

func observeMyProtocolType<T>(_ object: T) where T:Enabled, T:NSObject {
    let _ = object.observe(\.isEnabled, options: [.new]) { _, _ in
        print("changed")
    }
}

observeMyProtocolType(c)
// this fails