safe money

main.dart

abstract class Currency {
  const Currency(this.precision, this.currencyCode);

  final int precision;
  final String currencyCode;
  
  static List<Currency> all() {
    return [Chf(), Xbt()];
  }
}

class Xbt extends Currency {
  const Xbt() : super(8, 'XBT');
}

class Chf extends Currency {
  const Chf() : super(2, 'CHF');
}

class Money<T extends Currency> {
  Money(this.amount);

  final int amount;

  int get precision {
    return _currency.precision;
  }
  
  String get currencyCode {
    return _currency.currencyCode;
  }
  
  Currency get _currency => Currency.all().firstWhere((c) => c.runtimeType == T);
  
  @override
  String toString() => 'Money($amount, $currencyCode)';
}

void main() {
  var m1 = Money<Chf>(100);
  print(m1);
  print(m1.precision);
  
  var m2 = Money<Xbt>(1);
  print(m2);
  print(m2.precision);
}