feat: SyncJSON — ship the Sendable JSON payload carrier in the library - #672
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sync(...) runs off the main actor, so a payload crossing into it must be Sendable — which [String: Any] is not. Consumers were left to hand-roll a Sendable JSON box (the demo had DemoSyncPayload + DemoSyncValue, ~120 lines). Ship it once in the library instead: - SyncJSON: a Sendable enum JSON value conforming to SyncPayloadConvertible, with init(dictionary:), toSyncPayloadDictionary(), and keyed accessors (string/objectArray). NSNumber matched first so JSON bools aren't read as 1. Preserves null (so a sync can clear) and value shapes. - Demo drops DemoSyncPayload/DemoSyncValue entirely and uses SyncJSON. red-first: SyncJSONTests (round-trip, accessors, syncs as a payload). All green: SwiftSync 178, DemoCore 43, DemoBackend 32. README documents it.
3lvis
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June 27, 2026 08:26
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Why
sync(...)runs off the main actor, so a payload crossing into it must beSendable. A raw[String: Any]isn't — so any consumer that decodes JSON on one actor and syncs it on another has to hand-roll aSendableJSON box. The demo had exactly that:DemoSyncPayload+DemoSyncValue, ~120 lines of generic boilerplate every consumer would otherwise reinvent.This ships that carrier once, in the library.
What
SyncJSON— aSendableenum JSON value conforming toSyncPayloadConvertible, so it feedssync(payload:)/sync(item:)directly.init(dictionary:),toSyncPayloadDictionary(), and keyed accessors (string(_:),objectArray(_:)).NSNumberis matched first so a JSON boolean isn't read as1(the classic bridging trap). Preservesnull(so a sync can clear a field) and the value shapes.DemoSyncPayload/DemoSyncValueand usesSyncJSONthroughout — net deletion of the duplicated box.Why this one earns its place (unlike the recent detours)
It has a present consumer (the demo adopts it in the same PR) and removes real duplication every consumer would hit — not speculative surface. It's the genuine library-ergonomics gap we traced from the
DemoSyncPayloaddiscussion: SwiftSync made consumers BYO-Sendable-JSON; now it doesn't.Verification
Red-first
SyncJSONTests(round-trip, keyed accessors, syncs as aSyncPayloadConvertible). All green: SwiftSync 178, DemoCore 43, DemoBackend 32. README documents the type.