I am converting a Swift iOS project to Swift 3.0 using Xcode 8 Beta 4. The absolute value function shows to be unavailable. Here is a code sample...
let myInt = -3
let myAbsoluteInt = abs(myInt)
'abs' is unavailable: Please use the 'abs(_:)' free function
The code you're showing us works for me in Xcode 8 beta 4.
I suppose you have another, different issue causing this misleading error message.
For example, it could be a conflict if you have imported other libraries.
A quick workaround would be to use the complete type:
let myAbsoluteInt = Swift.abs(myInt)