A developer shares the experience of rewriting Wally, an iOS wallet app, for iOS 16 and SwiftUI 4. Key changes include extracting app-agnostic code into a local Swift package (WallyKit) to speed up builds and improve separation of concerns, adopting SwiftUI 4 features like NavigationSplitView, Transferable, async/await, and new toolbars, and replacing Quick & Nimble with XCTest. The rewrite also introduces a generic WalletItemStore protocol using the decorator pattern to support multiple item types (cards, receipts, notes, photos) without duplicating code. Realm is retained for data persistence, a skinning system is added via SwiftUI theming, and StoreKit 2 is integrated for a new premium subscription model.
