A function to assign device specific value for UIKit.

ForDevice.swift

// Swift 3.0:
// This functuion makes use of the custom operator `?!`:
// https://gist.github.com/DevAndArtist/dad641ee833e60b02fd1db2dbb488c6a

@available(iOS 9.0, *)
func forDevice<T>(
    phone: @autoclosure () -> T? = nil,
      pad: @autoclosure () -> T? = nil,
       tv: @autoclosure () -> T? = nil,
  carPlay: @autoclosure () -> T? = nil) -> T {

	let idiom = UIDevice.current.userInterfaceIdiom

	switch idiom {
	case .phone:
		return phone() ?! fatalError("`phone` unspecified")
	case .pad:
		return pad() ?! fatalError("`pad` unspecified")
	case .tv:
		return tv() ?! fatalError("`tv` unspecified")
	case .carPlay:
		return carPlay() ?! fatalError("`carPlay` unspecified")
	default:
		fatalError()
	}
}