main.dart

enum PlanetType { terrestrial, gas, ice }

/// 太陽系の惑星を列挙する
enum Planet {
  mercury(planetType: PlanetType.terrestrial, moons: 0, hasRings: false),
  venus(planetType: PlanetType.terrestrial, moons: 0, hasRings: false),
  // ···
  uranus(planetType: PlanetType.ice, moons: 27, hasRings: true),
  neptune(planetType: PlanetType.ice, moons: 14, hasRings: true);

  /// `enum`のコンストラクタ
  const Planet(
      {required this.planetType, required this.moons, required this.hasRings});

  /// 変数はすべて`final`になります
  final PlanetType planetType;
  final int moons;
  final bool hasRings;

  /// getterやメソッドを定義できます
  bool get isGiant =>
      planetType == PlanetType.gas || planetType == PlanetType.ice;
}

void main() {
  final yourPlanet = Planet.venus;

  if (!yourPlanet.isGiant) {
    print('Your planet is not a "giant planet".');
  }
}