---
title: "isLeadSurrogate(_:)"
framework: swift
role: symbol
role_heading: Type Method
path: "swift/unicode/utf16/isleadsurrogate(_:)"
---

# isLeadSurrogate(_:)

Returns a Boolean value indicating whether the specified code unit is a high-surrogate code unit.

## Declaration

```swift
static func isLeadSurrogate(_ x: Unicode.UTF16.CodeUnit) -> Bool
```

## Parameters

- `x`: A UTF-16 code unit.

## Return Value

Return Value true if x is a high-surrogate code unit; otherwise, false.

## Discussion

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.