# update(from:) Updates the buffer slice’s initialized memory with the given elements. ``` func update(from source: S) -> (unwritten: S.Iterator, index: Slice.Index) where Base == UnsafeMutableBufferPointer, S : Sequence ``` ## Parameters `source` A sequence of elements to be used to update the contents of the buffer slice. ## Return Value An iterator to any elements of `source` that didn’t fit in the buffer slice, and the index one past the last updated element. ## Discussion The buffer slice’s memory must be initialized or its `Element` type must be a trivial type. --- 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)