# init(capacity:initializingWith:) Creates a new array with the specified capacity, directly initializing its storage using an output span. ``` init(capacity: Int, initializingWith body: @_lifetime(0: copy 0) (inout OutputSpan) throws(E) -> Void) throws(E) where E : Error ``` ## Parameters `capacity` The storage capacity of the new array. `body` A callback that gets called at most once to directly populate newly reserved storage within the array. The function is allowed to add fewer than `capacity` items. The array is initialized with however many items the callback adds to the output span before it returns (or before it throws an error). --- 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)