I may have to develop for iphone 4 and use Xcode 6. Does anyone know if Xcode 6 supports Swift 3? And if I would face any other serious issues in doing this?
Can you use Swift 3 in Xcode 6?
No, and not even Swift2.
Swift3 was introduced with XCode8.
Can have a look at wikipedia/XCode to find which version of Swift for which SCode