> I'd like to know if I can write an app in Swift that can run on iOS6.
No. From Xcode6 release notes:
"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."
No. From Xcode6 release notes:
"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."