Protocol to enable passing "context: CarriesBaggageContext"

[ktoso]

Goals:

• easily be used "in" frameworks without them having to "be" a (Baggage)Context
  • e.g. frameworkContext.theMetadataContext -- is nested, not "is"

What if we did

// in module Baggage
// so you'd `import Baggage`

protocol ContextCarrier { 
  var baggage: Context { get set }

  subscript<Key: ContextKey>(_ key: Key.Type) -> Key.Value? { get set }
}

struct Context { ... }

extension Context: ContextCarrier { 
  var baggage = self ... 
  ... 
}

This way other libs can:

• carry Context without being one
• the module name and type name don't clash:
  • module Baggage
  • and type name Context
• implement the "accessors" (var zipkinTrace: ...) on the BaggageContextCarrier protocol
  • and it become available on Context as well as "my-framework-context" (any of them for that matter 🎉 )

We do have disambiguation that it's the Baggage.Context is any other lib has a Context type and they'd clash.

For passing around:

• libs unaware of frameworks could use func hello(who: String, context: BaggageContextCarrier)
  • this way any library can call hello(who: "me", context: myFrameworkSpecificContext)
  • this can be optional though if they dont want to
  • if they lib does not do this, users would have to pass hello(who: "me", context: myFrameworkSpecificContext.baggage) which again reads quite well
  • or if they have the "raw" context they can pass context 👍

Let's explore this idea a bit 👀

[ktoso]

Moving this to the context repository

[ktoso]

cc @tomerd @tachyonics so that's a ticket from a while ago about the protocol libs could use. Other ideas and names and shapes quite welcome :)

[ktoso]

We could offer one which handles the logging bridge magic as separate module.

I'll be looking into this