# Subscriber A protocol that declares a type that can receive input from a publisher. ``` protocol Subscriber : CustomCombineIdentifierConvertible ``` ## Overview A [`Subscriber`](/documentation/Combine/Subscriber) instance receives a stream of elements from a [`Publisher`](/documentation/Combine/Publisher), along with life cycle events describing changes to their relationship. A given subscriber’s [`Input`](/documentation/Combine/Subscriber/Input) and [`Failure`](/documentation/Combine/Subscriber/Failure) associated types must match the [`Output`](/documentation/Combine/Publisher/Output) and [`Failure`](/documentation/Combine/Publisher/Failure) of its corresponding publisher. You connect a subscriber to a publisher by calling the publisher’s [`subscribe(_:)`](/documentation/Combine/Publisher/subscribe(_:)-4u8kn) method. After making this call, the publisher invokes the subscriber’s [`receive(subscription:)`](/documentation/Combine/Subscriber/receive(subscription:)) method. This gives the subscriber a [`Subscription`](/documentation/Combine/Subscription) instance, which it uses to demand elements from the publisher, and to optionally cancel the subscription. After the subscriber makes an initial demand, the publisher calls [`receive(_:)`](/documentation/Combine/Subscriber/receive(_:)), possibly asynchronously, to deliver newly-published elements. If the publisher stops publishing, it calls [`receive(completion:)`](/documentation/Combine/Subscriber/receive(completion:)), using a parameter of type [`Subscribers.Completion`](/documentation/Combine/Subscribers/Completion) to indicate whether publishing completes normally or with an error. Combine provides the following subscribers as operators on the [`Publisher`](/documentation/Combine/Publisher) type: - [`sink(receiveCompletion:receiveValue:)`](/documentation/Combine/Publisher/sink(receiveCompletion:receiveValue:)) executes arbitrary closures when it receives a completion signal and each time it receives a new element. - [`assign(to:on:)`](/documentation/Combine/Publisher/assign(to:on:)) writes each newly-received value to a property identified by a key path on a given instance. ## Topics ### Declaring supporting types [`Input`](/documentation/Combine/Subscriber/Input) The kind of values this subscriber receives. [`Failure`](/documentation/Combine/Subscriber/Failure) The kind of errors this subscriber might receive. ### Receiving elements [`receive(_:)`](/documentation/Combine/Subscriber/receive(_:)) Tells the subscriber that the publisher has produced an element. [`receive()`](/documentation/Combine/Subscriber/receive()) Tells the subscriber that a publisher of void elements is ready to receive further requests. ### Receiving life cycle events [`receive(subscription:)`](/documentation/Combine/Subscriber/receive(subscription:)) Tells the subscriber that it has successfully subscribed to the publisher and may request items. [`receive(completion:)`](/documentation/Combine/Subscriber/receive(completion:)) Tells the subscriber that the publisher has completed publishing, either normally or with an error. [`Completion`](/documentation/Combine/Subscribers/Completion) A signal that a publisher doesn’t produce additional elements, either due to normal completion or an error. ## Relationships ### Conforming Types [`Assign`](/documentation/Combine/Subscribers/Assign) [`AnySubscriber`](/documentation/Combine/AnySubscriber) [`Sink`](/documentation/Combine/Subscribers/Sink) ### Inherits From [`CustomCombineIdentifierConvertible`](/documentation/Combine/CustomCombineIdentifierConvertible) --- 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)