# init(referencing:) Initialize a `Data` by adopting a reference type. ``` init(referencing reference: NSData) ``` ## Parameters `reference` The instance of `NSData` that you wish to wrap. This instance will be copied by `struct Data`. ## Discussion You can use this initializer to create a `struct Data` that wraps a `class NSData`. `struct Data` will use the `class NSData` for all operations. Other initializers (including casting using `as Data`) may choose to hold a reference or not, based on a what is the most efficient representation. If the resulting value is mutated, then `Data` will invoke the `mutableCopy()` function on the reference to copy the contents. You may customize the behavior of that function if you wish to return a specialized mutable subclass. --- 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)