SE-0362: Piecemeal adoption of future language improvements

[ebg]

How can we extend this to OS version checking? There is a real gap when adopting new capabilities between WWDC and the Fall OS releases.

Do we need something like '#if available'?

During the beta period of Xcode 12, we wanted to start implementing features that relied on the new SDK, but still keep our code compiling with the previous SDK. I've found myself wanting to do a compile-time check on the availability of certain SDKs. For example, I would want to write code like this: func doStuff() { if #available(macOS 11.0, *) { // Use macOS 11.0-only code WidgetCenter.shared.reloadAllTimelines() } } However, the above code wouldn't compile at all with Xcode 11…