# 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] ``` ## Relationships ### Conforms To [`ConvertibleFromBytes`](/documentation/Swift/ConvertibleFromBytes) [`Hashable`](/documentation/Swift/Hashable) [`Escapable`](/documentation/Swift/Escapable) [`BidirectionalCollection`](/documentation/Swift/BidirectionalCollection) [`ConvertibleToBytes`](/documentation/Swift/ConvertibleToBytes) [`Copyable`](/documentation/Swift/Copyable) [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`CustomReflectable`](/documentation/Swift/CustomReflectable) [`Equatable`](/documentation/Swift/Equatable) [`Collection`](/documentation/Swift/Collection) [`Sequence`](/documentation/Swift/Sequence) [`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible) [`Sendable`](/documentation/Swift/Sendable) [`BitwiseCopyable`](/documentation/Swift/BitwiseCopyable) [`MutableCollection`](/documentation/Swift/MutableCollection) [`RandomAccessCollection`](/documentation/Swift/RandomAccessCollection) [`ContiguousBytes`](/documentation/Foundation/ContiguousBytes) --- 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)