[swift-evolution] [swift-dev] [Swift 4] Organizing source stability

[Douglas Gregor]

> On Aug 3, 2016, at 1:16 AM, Brent Royal-Gordon via swift-dev <swift-dev at swift.org> wrote:
> 
>> On Jul 29, 2016, at 5:55 PM, Jacob Bandes-Storch via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> 	• a top-of-file "shebang"-style comment indicating the version, something like //#swift(4), mirroring the "#if swift" syntax
> 
> `import Swift 3.1`?
> 
> I think this brings up two interesting questions:
> 
> * Do we want to be able to mix files using different versions of Swift in the same module?

No. It simplifies the problem greatly if the whole module is compiled with a single Swift version.

> * Do we want to extend these backwards compatibility features beyond the standard library to other modules?

If we can design generally-useful features for handling language versioning, that the standard library can adopt, that would be great.

	- Doug