# init(unsafeUninitializedCapacity:initializingWith:) Creates an array with the specified capacity, and then calls the given closure with a buffer covering the array’s uninitialized memory. ``` init(unsafeUninitializedCapacity: Int, initializingWith initializer: (inout UnsafeMutableBufferPointer, inout Int) throws(E) -> Void) throws(E) where E : Error ``` ## Parameters `unsafeUninitializedCapacity` The number of elements to allocate space for in the new array. `initializer` A closure that initializes elements and sets the count of the new array. - Parameters: - buffer: A buffer covering uninitialized memory with room for the specified number of elements. - initializedCount: The count of initialized elements in the array, which begins as zero. Set `initializedCount` to the number of elements you initialize. ## Discussion Inside the closure, set the `initializedCount` parameter to the number of elements that are initialized by the closure. The memory in the range `buffer[0.. Note: While the resulting array may have a capacity larger than the > requested amount, the buffer passed to the closure will cover exactly > the requested number of elements. --- 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)