Pitch: Automatic inclusion of new standard library features when supporting older versions of Swift

[tkrajacic (Thomas Krajacic)]

I think this is similar to the question I asked a while ago on how to "polyfill" features for previous releases?

Best way to implement new feature for old SDKs

Heh. I did put that in there deliberately, but no, not that I know of. There's nothing incredibly technically difficult in making this work: @dynamicallyAvailableBefore(macOS 10.12) var temporaryDirectory: URL { … } and having the compiler check that the signature matches up and everything before generating the code you wrote above. But it'd be a proposal that needs a lot of careful thought—how does this affect how people use framework code? What happens on new platforms? What if two people do…

I think it would be incredibly useful especially since we have ABI stability.