# copyBytes(from:) Copies from a collection of `UInt8` into this buffer slice’s memory. ``` func copyBytes(from source: C) where C : Collection, C.Element == UInt8 ``` ## Parameters `source` A collection of `UInt8` elements. `source.count` must be less than or equal to this buffer slice’s `count`. ## Discussion If the first `source.count` bytes of memory referenced by this buffer slice are bound to a type `T`, then `T` must be a trivial type, the underlying pointer must be properly aligned for accessing `T`, and `source.count` must be a multiple of `MemoryLayout.stride`. After calling `copyBytes(from:)`, the first `source.count` bytes of memory referenced by this buffer slice are initialized to raw bytes. If the memory is bound to type `T`, then it contains values of type `T`. --- 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)