# isLeadSurrogate(_:) Returns a Boolean value indicating whether the specified code unit is a high-surrogate code unit. ``` static func isLeadSurrogate(_ x: Unicode.UTF16.CodeUnit) -> Bool ``` ## Parameters `x` A UTF-16 code unit. ## Return Value `true` if `x` is a high-surrogate code unit; otherwise, `false`. ## Discussion Here’s an example of checking whether each code unit in a string’s `utf16` view is a lead surrogate. The `apple` string contains a single emoji character made up of a surrogate pair when encoded in UTF-16. ``` let apple = "🍎" for unit in apple.utf16 { print(UTF16.isLeadSurrogate(unit)) } // Prints "true" // Prints "false" ``` This method does not validate the encoding of a UTF-16 sequence beyond the specified code unit. Specifically, it does not validate that a low-surrogate code unit follows `x`. --- 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)