DifferenceKit in Action try! Swift Tokyo 2020 Meetup!! Jan 2020

Ryo Aoyama CyberAgent, Inc. CATS productivity team Twitter: @ra1028fe5 GitHub: @ra1028 OSS: DifferenceKit, Carbon, swift-mod, etc…

DifferenceKit https://github.com/ra1028/DifferenceKit Ver: 1.1.5 Star: 2.3k Fork: 133 A fast and flexible O(n) difference algorithm framework for Swift collection.

Works on many production app LINE Mercari Uber CyberAgent Yahoo Japan PayPay dely NIKKEI and more… eureka

Why we use diffing algorithm • For performance • For beautiful animation • For declarative programming • For business logic segregation

Ordered N-items List UI

When insert an item to the list, reloadDate() will calculates for all items. It’s not efficient Reload

UI calculations are very slow and will force the main thread. Reload Slow Slow Slow Slow

Improving list UI performance by updating only the differences. Reload Slow

performBatchUpdates can partially update items with animations let deleteIndexPaths: [IndexPath] let insertIndexPaths: [IndexPath] let moveIndexPaths: (from: IndexPath, to: IndexPath) let reloadIndexPaths: [IndexPath] tableView.performBatchUpdates({ tableView.deleteRows(at: deleteIndexPaths, with: .automatic) tableView.insertRows(at: insertIndexPaths, with: .automatic) tableView.moveRow(at: moveIndexPaths.from, to: moveIndexPaths.to) tableView.reloadRows(at: reloadIndexPaths, with: .automatic) })

Now, do you know which item was inserted?

How can I programmatically know how the item array requested to the network has changed?

Diffing algorithm Calculates the diffs before and after updating the array. https://en.wikipedia.org/wiki/Diff Wiki:

DifferenceKit let source: [Item] let target: [Item] let changeset = StagedChangeset(source: source, target: target) tableView.reload(using: changeset, with: .automatic) { data in self.data = data }

Paul Heckel’s Algorithm DifferenceKit uses… Paper: A technique for isolating differences between files https://dl.acm.org/doi/10.1145/359460.359467 With O(N) complexity, linear function time can be expected regardless of data size and changes. Ideal for UI calculations, IMO.

Paul Heckel’s Algorithm DifferenceKit uses… Optimizations in terms of + • Algorithm • Swift lang

Major Diffing Algorithms Author Myers Wu Heckel complexity O(ND) O(NP) O(N) insert ✅ ✅ ✅ delete ✅ ✅ ✅ move ⚠ ⚠ ✅ update ❌ ❌ ✅ shortest? Yes Yes No http://www.xmailserver.org/diff2.pdf http://documents.scribd.com/docs/10ro9oowpo1h81pgh1as.pdf https://publications.mpi-cbg.de/Wu_1990_6334.pdf

Swift Library Comparisons Disclaimer: These DO NOT compete for the “Best” of the library.

Library Algorithms

Performance Comparison • 3x slower • 20x slower • 7x slower • 18x slower • 4500x slower • 5400x slower • 140x slower From 100,000 elements to 10,000 deleted, 10,000 inserted and 2,000 shuffled BLAZING FAST !

Functionality Comparison Supported Collection

Functionality Comparison Supported Element Diff

Functionality Comparison Supported Section Diff

DifferenceKit in Future

DiffableDataSource https://developer.apple.com/videos/play/wwdc2019/220/ is pretty solid solution for diffing in list UI items. But, DifferenceKit is more loosely-coupled, white-boxed and for any usage (mainly UI).

SwiftUI https://developer.apple.com/xcode/swiftui/ New generation, personally, I hope SwiftUI will eliminate the DifferenceKit. Currently, SwiftUI.List has no customizability. We should use UITableView and UICollectionView as before. DifferenceKit will be useful for a while.

Thanks Twitter: @ra1028fe5 GitHub: @ra1028 Ryo Aoyama