swift-concurrency-6-2

Single-threaded by default with explicit background offloading via @concurrent and isolated protocol conformances. Patterns for adopting Swift 6.2's concurrency model where code runs single-threaded by default and concurrency is introduced explicitly. Eliminates common data-race errors without sacrificing performance. In Swift 6.1 and earlier, async functions could be implicitly offloaded to background threads, causing data-race errors even in seemingly safe code: Swift 6.2 fixes this: async functions stay on the calling actor by default. MainActor types can now conform to non-isolated protocols safely: The compiler ensures the conformance is only used on the main actor: Protect global/static state with MainActor: Swift 6.2 introduces a mode where MainActor is inferred by default — no manual annotations needed: This mode is opt-in and recommended for apps, scripts, and other executable targets. When you need actual parallelism, explicitly offload with @concurrent : Important: This example requires Approachable Concurrency build settings — SE-0466 (MainActor default isolation) and SE-0461 (NonisolatedNonsendingByDefault). With these enabled, extractSticker stays on the caller's actor, making mutable state access safe. Without these settings, this code has a data race — the compiler will flag it.