How to write modern Swift well — modeling with value types, Swift 6 data-race safety and approachable concurrency (@concurrent, main-actor-by-default, actors, task groups), protocols and generics (some vs any), API design, performance and ARC, Swift Testing, macros, and the modern language features

Design and implement one-click post-purchase upsells and downsells that raise average order value without hurting the main conversion rate. Use when asked to increase AOV, add an upsell, cross-sell or downsell after checkout, build a one-click upsell flow, monetize the thank-you page, or when someon