# transform(updating:body:) Tracks the location of the provided ranges throughout the mutation closure, updating them to new ranges that represent the same effective locations after the mutation. ``` mutating func transform(updating ranges: inout [Range], body: (inout AttributedString) throws(E) -> Void) throws(E) where E : Error ``` ## Parameters `ranges` A list of ranges to track throughout the `body` closure. The updated array (after the function is called) is guaranteed to be the same size as the provided array. Updated ranges are located at the same indices as their respective original ranges in the input `ranges` array. `body` A mutating operation, or set of operations, to perform on the value of `self`. The value of `self` is provided to the closure as an `inout AttributedString` that the closure should mutate directly. Do not capture the value of `self` in the provided closure - the closure should mutate the provided `inout` copy. ## Discussion If updating the provided ranges is not possible (tracking failed) then this function will fatal error. Use the `Optional`-returning variants to provide custom fallback behavior. --- 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)