// // Copyright (c) 2018 Open Whisper Systems. All rights reserved. // public extension Collection { /// Returns the element at the specified index iff it is within bounds, otherwise nil. subscript (safe index: Index) -> Element? { return indices.contains(index) ? self[index] : nil } } public extension Array { func chunked(by chunkSize: Int) -> [[Element]] { return stride(from: 0, to: self.count, by: chunkSize).map { Array(self[$0..