# withUnsafeMutableBytes(_:) Mutates the raw bytes in the data’s buffer. ``` mutating func withUnsafeMutableBytes(_ body: (UnsafeMutablePointer) throws -> ResultType) rethrows -> ResultType ``` ## Discussion This function assumes that you are mutating the contents. > Warning: > The byte pointer argument should not be stored and used outside of the lifetime of the call to the closure. --- 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)