# CollectionOfOne A collection containing a single element. ``` @frozen struct CollectionOfOne ``` ## Overview You can use a `CollectionOfOne` instance when you need to efficiently represent a single value as a collection. For example, you can add a single element to an array by using a `CollectionOfOne` instance with the concatenation operator (`+`): ``` let a = [1, 2, 3, 4] let toAdd = 100 let b = a + CollectionOfOne(toAdd) // b == [1, 2, 3, 4, 100] ``` --- 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)