Update - As per Xcode 6 Beta 4
iOS 7 and OS X 10.9 minimum deployment target
The Swift compiler and Xcode now enforce a minimum deployment target of iOS 7 or OS X
Mavericks. Setting an earlier deployment target results in a build failure.
From Xcode 6 release note
So my previous answer(Shown below) will not be applicable to any further development. Swift will no longer available for iOS6 and below
A Swift application can be run on iOS?6. Even though many people are saying that Swift will support only iOS 7+ and OS?X 10.9+, from my experience it's not.
I have tested a simple application written completely in Swift in an iOS?6 device. It works perfectly fine. As Apple says, Swift code is binary compatible with Objective-C code. It uses the same compiler and runtime to create the binary.
Here is the code I have tested:
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let button = UIButton.buttonWithType(UIButtonType.System) as UIButton
button.frame = CGRectMake(100, 100, 100, 50)
button.backgroundColor = UIColor.greenColor()
button.setTitle("Test Button", forState: UIControlState.Normal)
button.addTarget(self, action: "buttonTapped:", forControlEvents: UIControlEvents.TouchUpInside)
self.view.addSubview(button)
}
func buttonTapped(sender: UIButton!) {
println("buttonTapped")
}
}
It is a simple application, just adding a button programmatically. My application contains only two files, AppDelegate.swift
and ViewController.swift
.
So if you are not using any new APIs added as part of the iOS?8 SDK or some Swift specific APIs (corresponding API is not available for Objective-C) your application will seamlessly work on iOS?6 or later (tested and working), even on iOS?5 (not tested). Most of the APIs in Swift are just the replacement of the existing Objective-C APIs. In fact they are the same in binary.
Note: As per Xcode 6 beta 4 for swift apps deployment target should be iOS 7 or OS X 10.9(see the above update). So swift will no longer available for iOS6 and below