# buffer(size:prefetch:whenFull:) Buffers elements received from an upstream publisher. ``` func buffer(size: Int, prefetch: Publishers.PrefetchStrategy, whenFull: Publishers.BufferingStrategy) -> Publishers.Buffer ``` ## Parameters `size` The maximum number of elements to store. `prefetch` The strategy to initially populate the buffer. `whenFull` The action to take when the buffer becomes full. ## Return Value A publisher that buffers elements received from an upstream publisher. ## Discussion Use [`buffer(size:prefetch:whenFull:)`](/documentation/Combine/Publisher/buffer(size:prefetch:whenFull:)) to collect a specific number of elements from an upstream publisher before republishing them to the downstream subscriber according to the [`Publishers.BufferingStrategy`](/documentation/Combine/Publishers/BufferingStrategy) and [`Publishers.PrefetchStrategy`](/documentation/Combine/Publishers/PrefetchStrategy) strategy you specify. If the publisher completes before reaching the `size` threshold, it buffers the elements and publishes them downstream prior to completion. --- 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)