Creat Singletone pattern in dart

main.dart

class LoginApi implements LoginApiProtocol {
  const LoginApi._sharedInstance();

  static const LoginApi _shared = LoginApi._sharedInstance();

  factory LoginApi.instance() => _shared;

  @override
  Future<LoginHandle?> login(
      {required String email, required String password}) {
    throw UnimplementedError();
  }
}