Dart Static Enum Pattern

main.dart

/// As of Dart 2.5, `enum` can still only support very simple use case.
/// To have a "rich enum" with custom value type and methods, we need
/// to use static class member. This is an example implementation.

void main() {
  final s1 = 'done', s2 = 'waiting';
  final done = Enum.parse(Status.values, s1);
  final waiting = Enum.parse(Status.values, s2);
  
  print(done);
  print(waiting);
  print(done.isGood);
}

abstract class Enum<A> {
  final A _value;
  A get value => _value;
  
  Enum(this._value);
 
  @override
  String toString() => _value.toString();
  
  /// Returns an instance of enum `B` by taking the first
  /// value equals to `a` from the given choices.
  static B parse<A, B extends Enum<A>>(List<B> choices, A a) {
    return choices.firstWhere((c) => c.toString() == a);
  }
}

class Status extends Enum<String> {
  static final done = Status('done');
  static final waiting = Status('waiting');
  
  static final values = [done, waiting];
  
  Status(String s) : super(s);
  
  // Sample method
  bool get isGood => this == done;
}