How to write a function result to instance variable

I have an error in 5 line

The instance member
‘generateId’ can’t be accessed in an initializer. Try replacing the
reference to the instance member with a different expression

what i shoud do to write a function result to instance variable?

import 'dart:math';


class User{
  int id = generateId(10); // error i here
  String firstName;
  String lastName;
  String eMail;
  String password;
  final DateTime regDate = DateTime.now();

  User(this.firstName, this.lastName, this.eMail, this.password,){
    id = generateId(10);
  }
  
  @override
  String toString() =>'User: \n$firstName \n$lastName';

  int generateId(int count){
    int result;
    List <int> nums = [];
    for (int i = 0; i < count; i++){
      nums.add((Random().nextInt(9) + 1).toInt());
    }
    result = int.parse(nums.join());
    return result;
  }
}





void main() {
  User newUser = User("D", "P", "example@ex.com", "password");

  print(newUser);
}

>Solution :

Well, since you have only a single constructor and that sets the id anyway, you can basically remove it:

This:

int id = generateId(10); // error i here

becomes:

late int id;

Done.

In case your really, really need that line, you could make the generateId method either a function instead of a class method, or you could make it static. That should work, too.