With all of the new and awesome APIs that come out every year for each successive iOS version, it can be tempting to just drop support for the previous versions of iOS, and just go completely to the new stuff. Of course though, we usually can’t do that for many reasons. As such, we need to support older versions of iOS, and maybe dropping the oldest ones after they just become too difficult to support, or when active users on that platform drop to a certain amount.
There have been ways to check for API availability for some time, by checking if something responds to a selector, or just checking the iOS version ourselves and using that in a normal Swift “if” statement. With the arrival of Swift 2 though, we have an even nicer version of API checking, that is even helped by Xcode itself. This allows Xcode to actually warn you if you try to use something that is unavailable on one of the deployment targets for your Swift app.