# init(capacity:initializingWith:) Creates an array with the specified capacity, and then calls the given closure with an output span covering the array’s uninitialized memory. ``` init(capacity: Int, initializingWith initializer: @_lifetime(span: copy span) (inout OutputSpan) throws(E) -> Void) throws(E) where E : Error ``` ## Parameters `capacity` The number of elements to allocate space for in the new array. `initializer` A closure that initializes the elements of the new array. - Parameters: - span: An `OutputSpan` covering uninitialized memory with space for the specified number of elements. ## Discussion Inside the closure, initialize elements by appending to the `OutputSpan`. The `OutputSpan` keeps track of memory’s initialization state, ensuring safety. Its `count` at the end of the closure will become the `count` of the newly-initialized array. > Note: While the resulting array may have a capacity larger than the > requested amount, the `OutputSpan` passed to the closure will cover > exactly the number of elements requested. --- 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)