print to stderr in Swift 3

PrintToStdErr.swift

// known-good: Xcode 8, Swift 3

import Foundation

var standardError = FileHandle.standardError

extension FileHandle : TextOutputStream {
  public func write(_ string: String) {
    guard let data = string.data(using: .utf8) else { return }
    self.write(data)
  }
}

print("I am printed to stderr",to:&standardError)