Extension in Dart

user.dart

import 'package:flutter/foundation.dart';

class User extends Object {
  final String userId;
  final String firstName;
  final String secondName;
  bool isActive;

   User({
    @required this.userId,
    @required this.firstName,
    @required this.secondName,
    @required this.isActive,
  });
}

extension UserExtention on User {
  static bool toggle() {
    return this.isActive = !this.isActive;
  }
}

final User = User(userId: '1', firstName: 'John', secondName: 'Doe', isActive: true);