[0xmohit]

As per the blog [0], you can expect a lot to break.

  Swift 3 is a source-breaking release, largely due to the
  changes in SE-0005 and SE-0006. These changes not only impact
  the names of the Standard Library APIs, but also completely
  change how Objective-C APIs (particularly from Cocoa) import
  into Swift. Many of the changes are largely mechanical, but
  they can be numerous in a typical Swift project.

  To help with moving to Swift 3, Xcode 8.0 contains a code
  migrator that can automatically handle many of the need source
  changes. There is also a migration guide available to guide you
  through many of the changes — especially through the ones that
  are less mechanical and require more direct scrutiny.

[0] https://swift.org/blog/swift-3-0-released/