# CFStringTransform(_:_:_:_:) Perform in-place transliteration on a mutable string. ``` func CFStringTransform(_ string: CFMutableString!, _ range: UnsafeMutablePointer!, _ transform: CFString!, _ reverse: Bool) -> Bool ``` ## Parameters `string` The string to transform. `range` A pointer to the range over which the transformation is applied. `NULL` causes the whole string to be transformed. On return, `range` is modified to reflect the new range corresponding to the original range. `transform` A CFString object that identifies the transformation to apply. For a list of valid values, see [Transform Identifiers for CFStringTransform](/documentation/CoreFoundation/transform-identifiers-for-cfstringtransform). In macOS 10.4 and later, you can also use any valid ICU transform ID defined in the [ICU User Guide for Transforms](https://unicode-org.github.io/icu/userguide/transforms/general/). `reverse` A Boolean that, if `true`, specifies that the inverse transform should be used (if it exists). ## Return Value `true` if the transform is successful; otherwise `false`. ## Discussion The transformation represented by `transform` is applied to the given range of `string`, modifying it in place. Only the specified range is modified, but the transform may look at portions of the string outside that range for context. Reasons that the transform may be unsuccessful include an invalid transform identifier, and attempting to reverse an irreversible transform. --- 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)