I'm new to Apple developing and soon I will distribute my app via AppStore. So now I'm using Swift 3 and by default the deployment target is set to iOS 10.0 It means that I won't be able to make it run for example on iOS 8-9? 'Cos in Swift 3 I use new funcs which are not available in later OS
You can make your app run on iOS 8 & 9 by setting the Deployment Target to one of these versions. Swift 3 is compatible with iOS 8 and newer (I'm not sure, but it might be also compatible with iOS 7). The only difference to Swift 2.2 (regarding the system requirements) is that you have to use Xcode 8.
When you set your Deployment Target to an earlier version than iOS 10, you should be aware that you cannot use APIs that are new in iOS 10. (except you use the
#available opearator) But using Swift 3 should be no problem.
Edit: You can now upload apps written in Swift 3 using Xcode 8.0 GM