Maybe in Dart

gistfile1.dart

library maybe;

abstract class Maybe<T> {
  T get value;
  bool get isEmpty;
}

class Nothing extends Maybe {
  get value => null;
  bool get isEmpty => true;

  String toString() => "Nothing";
}
var nothing = new Nothing();

class Just<T> extends Maybe<T> {
  T _value;
  T get value => _value;

  Just(this._value);
  bool get isEmpty => false;

  String toString() => "Just $value";
}


Maybe<double> divide(double a, double b) {
  if (b == 0) {
    return nothing;
  } else {
    return new Just(a / b);
  }
}

void main() {
  var result = divide(5.0, 2.0);
  if (result is Just) {
    print("Result - $result");
  } else if (result is Nothing) {
    print(result);
  }

  switch(result.isEmpty) {
    case true: print("Result - $result"); break;
    case false: print(result); break;
  }
}