# moveUpdate(fromContentsOf:) Updates this buffer’s initialized memory initialized memory by moving every element from the source buffer slice, leaving the source memory uninitialized. ``` func moveUpdate(fromContentsOf source: Slice>) -> UnsafeMutableBufferPointer.Index ``` ## Parameters `source` A buffer slice containing the values to move. The memory region underlying `source` must be initialized. ## Return Value An index one past the index of the last element updated. ## Discussion Prior to calling the `moveUpdate(fromContentsOf:)` method on a buffer, the first `source.count` elements of the buffer’s memory must be initialized, or the buffer’s `Element` type must be a trivial type. The memory referenced by `source` is uninitialized after the function returns. The buffer must reference enough initialized memory to accommodate `source.count` elements. The returned index is one past the index of the last element updated. If `source` contains no elements, the returned index is equal to the buffer’s `startIndex`. If `source` contains as many elements as the buffer can hold, the returned index is equal to the buffer’s `endIndex`. > Note: The memory regions referenced by `source` and this buffer > must not overlap. > Precondition: `self.count` >= `source.count` --- 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)