Understanding Discriminated Unions in Typescript

du-type-guards-update.ts

function evaluatePrice(vehicle: Vehicle) {
  switch(vehicle.vType) {
    case "car":
      return vehicle.transmission * evaluationFactor;
    case "truck":
      return vehicle.capacity * evaluationFactor;
    case "motorcycle":
      return vehicle.make * evaluationFactor;
    default:
      const invalidVehicle: never = vehicle;
      return throw new Error(`Unknown vehicle: ${invalidVehicle}`);
  }
}