Publishers.SwitchToLatest

struct · iOS 13.0+ · SDK 27.1

struct SwitchToLatest<P, Upstream> where P : Publisher, P == Upstream.Output, Upstream : Publisher, P.Failure == Upstream.Failure

A publisher that flattens nested publishers. Given a publisher that publishes ``Publisher`` instances, the ``Publishers/SwitchToLatest`` publisher produces a sequence of events from only the most recent one. For example, given the type `AnyPublisher<URLSession.DataTaskPublisher, NSError>`, calling ``Publisher/switchToLatest()`` results in the type `SwitchToLatest<(Data, URLResponse), URLError>`. The downstream subscriber sees a continuous stream of `(Data, URLResponse)` elements from what looks like a single <doc://com.apple.documentation/documentation/Foundation/URLSession/DataTaskPublisher> even though the elements are coming from different upstream publishers. When ``Publishers/SwitchToLatest`` receives a new publisher from the upstream publisher, it cancels its previous subscription. Use this feature to prevent earlier publishers from performing unnecessary work, such as creating network request publishers from frequently-updating user interface publishers.

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