[swift-evolution] [Proposal] Swift 2.2: #if swift language version

[Douglas Gregor]

> On Dec 18, 2015, at 12:29 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> 
>> On Dec 18, 2015, at 12:25 PM, Radosław Pietruszewski via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> Sounds like it could be super useful for libraries!
>> 
>> How about we drop the quote marks, though? If we have `os(iOS)` and `#available(iOS 9, *)` (in other context), why not `swift(2.2)`?
> 
> I agree with Radek.
> 
> The argument to use a string is if we wanted to support subversions, e.g. like “#if swift(2.2.1)”.  This requires the parameter to be a string, because 2.2.1 isn’t a valid floating point literal - the lexer will be displeased.
> 
> However, I don’t think we *want* the feature to be able to do that.  The most important use case for this feature is to handle syntactic differences across swift versions, and we don’t want those in sub-versions.  Given that, it seems better to keep the syntax clean and simple.


This feature LGTM, and I also prefer that we drop the quotes. Two levels of version number should be sufficient.

	- Doug

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