---
title: "init(mutating:)"
framework: Swift
role: symbol
role_heading: Initializer
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/mutablespan/init(mutating:)"
---

# init(mutating:)

Mutate untyped memory as a typed span.

## Declaration

```swift
init(mutating mutableBytes: inout MutableRawSpan)
```

## Parameters

- `mutableBytes`: A raw span to reinterpret as typed elements.

## Discussion

Discussion The byteCount of mutableBytes must be a multiple of Element’s stride, and the starting address of mutableBytes must be well-aligned for the type of Element. If either of these requirements is not met, this initializer will trap at runtime.