[Proposal Idea] Error: Sendable, AnySendable

Evolution Discussion
1

Two Concurrency proposals:

  1. Enforce Error to inherit Sendable.
  2. Add AnySendable type. Mainly for property-list data applications, to replace what's now [String: Any] with [String: AnySendable]. For example in WCSessionDelegate.
2

Can you provide more info here about your proposal? Error already inherits Sendable:

protocol Error : Sendable

Can you flesh out your idea with some examples of where AnySendable would be required over any Sendable?

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3

There is already any Sendable, and you can already write [String: any Sendable].

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4

And unfortunately, Any and any Sendable are not compatible with each other, so this is a breaking change for all existing users of any API that makes that change.

5

I do think there's an opportunity to special case any Hashable: Hashable the way any Error: Error (and any Sendable: Sendable). While AnyHashable has filled a gap in Swift for a long time, it does not compose with other protocols, so if you have a type that relies on AnyHashable for hashability and then need sendability, you're forced to make a decision and you may make an incorrect one.

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6

Exhibit A: Making AnyHashable Sendable

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Strangely I got some errors while was trying to send an error, so I assumed it's not sendable. Can't reproduce anymore, probably compiler errors were caused by other types.

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So yes, it would be good to update all the APIs to support concurrency. Both any Sendable and AnySendable should be equally good I think.