okla

extension DragGesture.Value {

  var velocity: CGPoint {

    let decelerationRate = UIScrollView.DecelerationRate.normal.rawValue,
      d = decelerationRate/(1000.0*(1.0 - decelerationRate))

    return CGPoint(x: (location.x - predictedEndLocation.x)/d,
      y: (location.y - predictedEndLocation.y)/d)
  }

okla

extension RawRepresentable {

  init?(rawValue optionalRawValue: RawValue?) {

    guard let rawValue = optionalRawValue, value = Self(rawValue: rawValue) else { return nil }

    self = value
  }
}