# init(upstream:size:prefetch:whenFull:) Creates a publisher that buffers elements received from an upstream publisher. ``` init(upstream: Upstream, size: Int, prefetch: Publishers.PrefetchStrategy, whenFull: Publishers.BufferingStrategy.Failure>) ``` ## Parameters `upstream` The publisher from which this publisher receives elements. `size` The maximum number of elements to store. `prefetch` The strategy for initially populating the buffer. `whenFull` The action to take when the buffer becomes full. --- 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)