protocol UserType {
    var id: UInt { get set }
    var name: String { get set }
}

struct User: UserType {

    var id: UInt
    var name: String

    init(id: UInt, name: String) {
        self.id = id
        self.name = name
    }
}

protocol Storage {
    func add(_ user: UserType)
    func delete(_ user: UserType)
}

final class RealmStorage: Storage {

    func add(_ user: UserType) {}

    func delete(_ user: UserType) {}

}

final class KeychainStorage: Storage {

    func add(_ user: UserType) {}

    func delete(_ user: UserType) {}

}

protocol UsersProtocol {
    func didLoad(_ users: [UserType])
    func didRemove(_ user: UserType)
}

final class UsersInteractor: UsersProtocol {

    let storage: Storage

    init(storage: Storage) {
        self.storage = storage
    }

    func didLoad(_ users: [UserType]) {
        users.forEach { storage.add($0) }
    }

    func didRemove(_ user: UserType) {
        storage.delete(user)
    }

}

let author = User(id: 999, name: "Maxim Vialykh")
let guest = User(id: 1, name: "Guest")
let users = [author, guest]

let usersInteractor = UsersInteractor(storage: RealmStorage())
usersInteractor.didLoad(users)

let spyInteractor = UsersInteractor(storage: KeychainStorage())
spyInteractor.didRemove(guest)