Init helper source: https://github.com/Ramotion/circle-menu/blob/master/CircleMenuLib/CircleMenu.swift

Init.swift

public func Init<Type>(value: Type, @noescape block: (object: Type) -> Void) -> Type {
  block(object: value)
  return value
}

let fade = Init(CABasicAnimation(keyPath: "opacity")) {
  $0.duration            = NSTimeInterval(duration)
  $0.fromValue           = fromOpacity
  $0.toValue             = toOpacity
  $0.timingFunction      = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
  $0.fillMode            = kCAFillModeForwards
  $0.removedOnCompletion = false
}