Enhanced enums were introduced in Dart 2.17 and are similar to regular classes, but they have a fixed set of instances.

They are more powerful than traditional enums as they can have properties, methods, and constructors.

Let’s pretend we’re building a weather app with an enum of seasons.

enum Season {
  spring,
  summer,
  fall,
  winter
}

In the past, if we wanted to add a corresponding image url and an average temperature to each season, we had a couple of options.

1. Create an extension.

/// Extension example.
extension SeasonX on Season {
  // Image url example.
  String getImageUrl(Season season) {
    switch (season) {
      case Season.spring:
        return '<spring_image_url>';
      case Season.summer:
        return '<summer_image_url>';
      case Season.fall:
        return '<fall_image_url>';
      case Season.winter:
        return '<winter_image_url>';
	  }
  }

	// ...
}

2. Turn Season into a class with factory constructors and three members (SeasonType type, String imageUrl, and double averageTemp).

/// Class example.
/// Note that I've renamed the `Season` enum to `SeasonType`.
class Season {
  const Season({
    required this.type,
    required this.imageUrl,
    required this.averageTemp,
  });

  factory Season.spring() => const Season(
        type: SeasonType.spring,
        imageUrl: '<spring_image_url>',
        averageTemp: 54,
      );

  // ...

  final SeasonType type;
  final String imageUrl;
  final double averageTemp;
}

With enhanced enums, we can simplify this by adding the member variables directly into the enum.

enum Season {
  spring('<spring_image_url>', 54),
  summer('<summer_image_url>', 81),
  fall('<fall_image_url>', 48),
  winter('<winter_image_url>', 32);

  const Season(this.imageUrl, this.averageTemp);

  final String imageUrl;
  final double averageTemp;

  void info() => print('''
    ${this.name}
    $imageUrl
    Average temperature: $averageTemp°F
    ''');
}

Now we can instantiate each Season while having access to the member variables and methods!

void main() {
  Season.spring.info();
  Season.summer.info();
  Season.fall.info();
  Season.winter.info();
}

// === Console ===
// spring
// <spring_image_url>
// Average temperature: 54°F

// summer
// <summer_image_url>
// Average temperature: 81°F

// fall
// <fall_image_url>
// Average temperature: 48°F

// winter
// <winter_image_url>
// Average temperature: 32°F