Enum values are always accessed using the enum's name. Therefore, it does not make any sense to prefix the enum's values with the enum's name. Doing so is repetitive and adds noise to the code.
enum Planet {
case PlanetMercury extends Planet
case PlanetVenus extends Planet
case PlanetEarth extends Planet
case PlanetMars extends Planet
// ...
}
enum Planet {
case Mercury extends Planet
case Venus extends Planet
case Earth extends Planet
case Mars extends Planet
// ...
}