# initialize(from:) Initializes the buffer’s memory with the given elements. ``` func initialize(from source: S) -> (unwritten: S.Iterator, index: UnsafeMutableBufferPointer.Index) where Element == S.Element, S : Sequence ``` ## Parameters `source` A sequence of elements with which to initialize the buffer. ## Return Value An iterator to any elements of `source` that didn’t fit in the buffer, and an index to the next uninitialized element in the buffer. ## Discussion Prior to calling the `initialize(from:)` method on a buffer, the memory it references must be uninitialized, or its `Element` type must be a trivial type. After the call, the memory referenced by the buffer up to, but not including, the returned index is initialized. The buffer must contain sufficient memory to accommodate `source.underestimatedCount`. The returned index is the position of the next uninitialized element in the buffer, which is one past the last element written. If `source` contains no elements, the returned index is equal to the buffer’s `startIndex`. If `source` contains an equal or greater number of elements than the buffer can hold, the returned index is equal to the buffer’s `endIndex`. --- 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)