---
title: "subscript(unchecked:)"
framework: Swift
role: symbol
role_heading: Instance Subscript
platforms: [iOS 12.2+, iPadOS 12.2+, Mac Catalyst 12.2+, macOS 10.14.4+, tvOS 12.2+, visionOS 1.0+, watchOS 5.2+]
path: "swift/mutablerawspan/subscript(unchecked:)"
---

# subscript(unchecked:)

Accesses the byte at the specified offset in the span.

## Declaration

```swift
subscript(unchecked byteOffset: Int) -> UInt8 { get set }
```

## Parameters

- `byteOffset`: The offset of the byte to access. byteOffset must be greater than or equal to zero, and less than byteCount.

## Overview

Overview This subscript does not validate byteOffset. Using this subscript with an invalid byteOffset results in undefined behaviour.