protocol UserProtocol {
    func login()
    func doSomeThing()
}

extension UserProtocol {
    func login() {
        print("default login")
    }

    func logout() {
        print("default logout")
    }
}

struct Student: UserProtocol {
    let name: String
    let id: Int

    func doSomeThing() {
        //You have to impleted this method because it has no implementation
    }

    // You can override *login* but it is not required and you can use it's default implementation
    // *logout* is also available to use
    func logout() {
        print("**Overriden logout**")
    }
}