# formUnion(_:) Adds the contents of the given range set to this range set. ``` mutating func formUnion(_ other: RangeSet) ``` ## Parameters `other` A range set to merge with this one. ## Discussion> Complexity: O(*m* + *n*), where *m* and *n* are the number of ranges in > this and the other range set. --- 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)