# init(validating:as:) Creates a new string by copying and validating the sequence of code units passed in, according to the specified encoding. ``` init?(validating codeUnits: some Sequence, as encoding: Encoding.Type) where Encoding : _UnicodeEncoding, Encoding.CodeUnit == UInt8 ``` ## Parameters `codeUnits` A sequence of code units that encode a `String` `encoding` A conformer to `Unicode.Encoding` that can decode `codeUnits` as `UInt8` ## Discussion This initializer does not try to repair ill-formed code unit sequences. If any are found, the result of the initializer is `nil`. The following example calls this initializer with the contents of two different arrays—first with a well-formed UTF-8 code unit sequence and then with an ill-formed ASCII code unit sequence. ``` let validUTF8: [Int8] = [67, 97, 0, 102, -61, -87] let valid = String(validating: validUTF8, as: UTF8.self) print(valid ?? "nil") // Prints "Café" let invalidASCII: [Int8] = [67, 97, -5] let invalid = String(validating: invalidASCII, as: Unicode.ASCII.self) print(invalid ?? "nil") // Prints "nil" ``` --- 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)