napkin — blog Posts on Swift 6 concurrency, iOS app architecture, dependency injection, actor testing, and modular iOS apps. https://getnapkin.to/blog/ 2026-05-16T00:00:00Z https://getnapkin.to/napkin-icon.png napkin https://getnapkin.to/ The Swift 6 @MainActor listener-conformance error, and a seam that sidesteps it https://getnapkin.to/blog/swift-6-mainactor-protocol-conformance/ 2026-05-16T00:00:00Z 2026-05-16T00:00:00Z "Main actor-isolated property 'listener' cannot be used to satisfy nonisolated protocol requirement" is the error every RIB-shaped listener seam hits under Swift 6. Why it happens, and the whole-protocol @MainActor design that makes it structurally impossible. A RIBs alternative for Swift Concurrency, without RxSwift: meet napkin https://getnapkin.to/blog/swift-6-ribs-replacement/ 2026-05-15T00:00:00Z 2026-05-15T00:00:00Z Uber's RIBs is alive, well, and actively developed. It's also built on RxSwift and ships a runtime leak detector. napkin is the same Router-Interactor-Builder pattern written for Swift Concurrency, without either — Clean Architecture on a napkin. Actor isolation for iOS app architecture in Swift 6 https://getnapkin.to/blog/swift-6-actor-isolation-architecture/ 2026-05-12T00:00:00Z 2026-05-12T00:00:00Z Swift 6 makes you declare where every piece of code runs. That's an architecture decision in disguise. Here's the four-ring isolation map napkin uses and why business logic belongs off the main actor. Dependency injection in SwiftUI without third-party libraries https://getnapkin.to/blog/swiftui-dependency-injection-without-libraries/ 2026-05-08T00:00:00Z 2026-05-08T00:00:00Z SwiftUI's @Environment wasn't designed for services. @EnvironmentObject crashes at runtime. There's a third option that's been around since RIBs and works cleanly with Swift 6 actors. Testing Swift actors: a practical guide https://getnapkin.to/blog/testing-swift-actors-guide/ 2026-05-05T00:00:00Z 2026-05-05T00:00:00Z If your business logic is in final actor types, you can unit-test it without a simulator. Mock the protocols, drive the lifecycle, assert on recorded calls. Modular iOS apps with Swift Concurrency https://getnapkin.to/blog/modular-ios-apps-swift-concurrency/ 2026-05-01T00:00:00Z 2026-05-01T00:00:00Z Modularity isn't a build-system question. It's about whether features can be reasoned about in isolation. Here's how to compose an iOS app as a tree of small, isolated units in Swift 6.