# moveUpdate(fromContentsOf:) Updates this buffer slice’s initialized memory by moving every element from the source buffer, leaving the source memory uninitialized. ``` func moveUpdate(fromContentsOf source: UnsafeMutableBufferPointer) -> Slice.Index where Base == UnsafeMutableBufferPointer ``` ## Parameters `source` A buffer 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 The region of memory starting at the beginning of this buffer slice and covering `source.count` instances of its `Element` type must be initialized, or its `Element` type must be a trivial type. After calling `moveUpdate(fromContentsOf:)`, the region of memory underlying `source` is uninitialized. The buffer slice 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 slice can hold, the returned index is equal to the slice’s `endIndex`. > Note: The memory regions referenced by `source` and this buffer slice > 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)