iOS Compatibility on different iOS Operation Systems

Question

I wanted to ask how compatibility on different iOS operation systems works in iOS. For example If I develop an app on Xcode 9.2 and Swift 4 for i

Answer 1

Very simple solution:

Set deployment target as 9.0 in your build target general settings. iOS will automatically handle support from 9.0 onwards for a build (your app).

Your app/build will be allowed to use/import frameworks and other libraries, compatible to minimum deployment target, only.

More detail about App Deployment Target from Apple.