protocol Item {
    var identifier: String { get }
    var name: String { get set }
}

struct SomeItem: Item {
  let identifier: String = UUID().uuidString
  var name: String = "New Item"
}

protocol ItemManager {

    /// get some objects matching query criteria
    func objects(matching query: Query) -> [Item]

    /// get a specific object
    func object(withID identifier: String) -> Item?

    /// commit these to disk.
    func save(_ object: Item) throws

    /// deletes the objects from disk.
    func delete(_ objects: [Item])

    /// creates a new object but does not save it.
    func create() -> Item
}