# NSHashInsertKnownAbsent(_:_:) Adds an element to the specified hash table. ``` func NSHashInsertKnownAbsent(_ table: NSHashTable, _ pointer: UnsafeRawPointer?) ``` ## Discussion Inserts `pointer`, which must not be `NULL`, into `table`. Unlike `NSHashInsert`, this function raises `NSInvalidArgumentException` if `table` already includes an element that matches `pointer`. ## See Also [`NSHashRemove`](/documentation/Foundation/NSHashRemove(_:_:)) Removes an element from the specified hash table. [`NSHashInsert`](/documentation/Foundation/NSHashInsert(_:_:)) Adds an element to the specified hash table. [`NSHashInsertIfAbsent`](/documentation/Foundation/NSHashInsertIfAbsent(_:_:)) Adds an element to the specified hash table only if the table does not already contain the element. --- 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)