# withUnsafeMutablePointer(to:_:) Calls the given closure with a mutable pointer to the given argument. ``` func withUnsafeMutablePointer(to value: inout T, _ body: (UnsafeMutablePointer) throws(E) -> Result) throws(E) -> Result where E : Error, T : ~Copyable, Result : ~Copyable ``` ## Parameters `value` An instance to temporarily use via pointer. Note that the `inout` exclusivity rules mean that, like any other `inout` argument, `value` cannot be directly accessed by other code for the duration of `body`. Access must only occur through the pointer argument to `body` until `body` returns. `body` A closure that takes a mutable pointer to `value` as its sole argument. If the closure has a return value, that value is also used as the return value of the `withUnsafeMutablePointer(to:_:)` function. The pointer argument is valid only for the duration of the function’s execution. ## Return Value The return value, if any, of the `body` closure. ## Discussion The `withUnsafeMutablePointer(to:_:)` function is useful for calling Objective-C APIs that take in/out parameters (and default-constructible out parameters) by pointer. The pointer argument to `body` is valid only during the execution of `withUnsafeMutablePointer(to:_:)`. Do not store or return the pointer for later use. --- 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)