Right now i'm using xcode 7.2.1 and planning to upgrade to 7.3.1, my question is, xcode 7.3.1 has swift 2.2 and 7.2.1 has swift 2.1. there are some new functionalities added and old ones are removed by apple. so, is it ok to upgrade to 7.3.1? will it affect my current project? (which is in swift 2.1)
It definitely will affect your current project. But the changes shouldn't be that bad. Of course this depends on your project.
That's the situation with Swift right now and that won't change until the language becomes more stable.