# Identifiable A class of types whose instances hold the value of an entity with stable identity. ``` protocol Identifiable ``` ## Overview Use the `Identifiable` protocol to provide a stable notion of identity to a class or value type. For example, you could define a `User` type with an `id` property that is stable across your app and your app’s database storage. You could use the `id` property to identify a particular user even if other data fields change, such as the user’s name. `Identifiable` leaves the duration and scope of the identity unspecified. Identities can have any of the following characteristics: - Guaranteed always unique, like UUIDs. - Persistently unique per environment, like database record keys. - Unique for the lifetime of a process, like global incrementing integers. - Unique for the lifetime of an object, like object identifiers. - Unique within the current collection, like collection indices. It’s up to both the conformer and the receiver of the protocol to document the nature of the identity. # Conforming to the Identifiable Protocol `Identifiable` provides a default implementation for class types (using `ObjectIdentifier`), which is only guaranteed to remain unique for the lifetime of an object. If an object has a stronger notion of identity, it may be appropriate to provide a custom implementation. ## Topics ### Specifying the Associated Type [`ID`](/documentation/Swift/Identifiable/ID-swift.associatedtype) A type representing the stable identity of the entity associated with an instance. ### Specifying the Identified Item [`id`](/documentation/Swift/Identifiable/id-8t2ws) The stable identity of the entity associated with this instance. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)