# append(addingCapacity:initializingWith:) Grows the array to have enough capacity for the specified number of elements, then calls the closure with an output span covering the array’s uninitialized memory. ``` mutating func append(addingCapacity uninitializedCount: Int, initializingWith initializer: @_lifetime(span: copy span) (inout OutputSpan) throws(E) -> Void) throws(E) where E : Error ``` ## Parameters `uninitializedCount` The number of new elements the array should have space for. `initializer` A closure that initializes new elements. - Parameters: - span: An `OutputSpan` covering uninitialized memory with space for the specified number of additional elements. ## Discussion Inside the closure, initialize elements by appending to `span`. It ensures safety by keeping track of the initialization state of the memory At the end of the closure, `span`’s `count` elements will have been appended to the array. If the closure throws an error, the items appended until that point will remain in the array. --- 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)