Good question. The “Versioned API” design is for testing a run-time 
property—it’s asking whether, dynamically, a particular library version is 
available (#available) or can be assumed available (@available) across the 
whole process. Since the Swift 4 compiler will use one runtime and standard 
library whether it’s in 3 mode or 4 mode, checking a run-time property isn’t 
the semantics we want. This proposal is concerned with the Swift language 
version at the time of compilation, and only for this particular module. 
(That’s also why there’s no #available component to the proposal.)

Thanks for bringing this up.
Jordan


> On Sep 26, 2016, at 10:06, Ben Rimmington via swift-evolution 
> <[email protected]> wrote:
> 
> Re: 
> <https://github.com/apple/swift-evolution/blob/master/proposals/0141-available-by-swift-version.md>
> 
> Is the "Versioned API" design in docs/LibraryEvolution.rst not intended for 
> the Swift standard library?
> 
> <https://jrose-apple.github.io/swift-library-evolution/#using-versioned-api>
> 
> <https://jrose-apple.github.io/swift-library-evolution/#publishing-versioned-api>
> 
> -- Ben
> 
> _______________________________________________
> swift-evolution mailing list
> [email protected]
> https://lists.swift.org/mailman/listinfo/swift-evolution

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