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

[Andrey Tarantsov]

> My experience with other languages is that [...] unless you're a Boost maintainer, people tend to target one version of the language anyway, either the older one using a workaround portable to the newer version, or the new version without regards to people stuck behind.

That's not how it works with Apple. Every summer we get a new beta version of Xcode with a new version of Swift, which we should use for all new developments (because it'll become the shipping version in the fall), but we have to use an older one for App Store-ready products if we want to be able to submit updates. So libraries do often support several versions of the language.

Just look the libraries that still support dual ARC/non-ARC modes, which is something that's not necessary at all.

A.