main.dart

class Validator {
  
  static Map<String, Function> _rules = {
    'required': (String value) {
      if (value.isEmpty) return false;
      return true;
    },
    // extends to support more rules,
    // such as between:1,10
    // min:1
    // max:10
  };
  
  static bool validate(String rule, String value) {
    // TODO, check if the rule exists
    return Validator._rules[rule](value);
  }
}

void main() {
  print(Validator.validate('required', '123'));
}