---
title: "transcodedLength(of:decodedAs:repairingIllFormedSequences:)"
framework: swift
role: symbol
role_heading: Type Method
path: "swift/unicode/utf16/transcodedlength(of:decodedas:repairingillformedsequences:)"
---

# transcodedLength(of:decodedAs:repairingIllFormedSequences:)

Returns the number of UTF-16 code units required for the given code unit sequence when transcoded to UTF-16, and a Boolean value indicating whether the sequence was found to contain only ASCII characters.

## Declaration

```swift
static func transcodedLength<Input, Encoding>(of input: Input, decodedAs sourceEncoding: Encoding.Type, repairingIllFormedSequences: Bool) -> (count: Int, isASCII: Bool)? where Input : IteratorProtocol, Encoding : _UnicodeEncoding, Input.Element == Encoding.CodeUnit
```

## Parameters

- `input`: An iterator of code units to be translated, encoded as sourceEncoding. If repairingIllFormedSequences is true, the entire iterator will be exhausted. Otherwise, iteration will stop if an ill-formed sequence is detected.
- `sourceEncoding`: The Unicode encoding of input.
- `repairingIllFormedSequences`: Pass true to measure the length of input even when input contains ill-formed sequences. Each ill-formed sequence is replaced with a Unicode replacement character ("\u{FFFD}") and is measured as such. Pass false to immediately stop measuring input when an ill-formed sequence is encountered.

## Return Value

Return Value A tuple containing the number of UTF-16 code units required to encode input and a Boolean value that indicates whether the input contained only ASCII characters. If repairingIllFormedSequences is false and an ill-formed sequence is detected, this method returns nil.

## Discussion

Discussion The following example finds the length of the UTF-16 encoding of the string "Fermata 𝄐", starting with its UTF-8 representation. let fermata = "Fermata 𝄐" let bytes = fermata.utf8 print(Array(bytes)) // Prints "[70, 101, 114, 109, 97, 116, 97, 32, 240, 157, 132, 144]"

let result = UTF16.transcodedLength(of: bytes.makeIterator(),                                     decodedAs: UTF8.self,                                     repairingIllFormedSequences: false) print(result) // Prints "Optional((count: 10, isASCII: false))"