It's really going crazy, this single simple line doesn't compile, why?

I'm using Xcode Version 8.1 (8B62)
Here's the api reference for String(format: String, _ arguments: CVarArg...)
It's really going crazy, this single simple line doesn't compile, why?

I'm using Xcode Version 8.1 (8B62)
Here's the api reference for String(format: String, _ arguments: CVarArg...)
On
It's really embarrassing to find that String(format: String, _ arguments: CVarArg...) is part of Foundation and not an default constructor....
The solution is that put import Foundation on the top of the playground
Add
import Foundationto the top of your playground.This will import the Foundation Framework and will allow you to use its API.