1. string type

main(List<String> args) {
  String name = "huhx";
  changIt(name);
  print('after: $name'); // after: huhx
}

void changIt(String name) {
  print('before: $name'); // before: huhx
  name = "linux";
}

2. reference Type

class User {
  String name;

  User(this.name);
}

main(List<String> args) {
  User user = User("huhx");
  changIt(user);
  print('after: ${user.name}'); // after: linux
}

void changIt(User user) {
  print('before: ${user.name}'); // before: huhx
  user.name = "linux";
}

3. deep clone

import 'dart:convert';

class User {
  String name;

  User(this.name);

  factory User.fromJson(Map<String, dynamic> userMap) => User(userMap['name']);

  Map<String, dynamic> toJson() => {'name': this.name};

  User clone() {
    final String jsonString = json.encode(this);
    final jsonResponse = json.decode(jsonString);

    return User.fromJson(jsonResponse as Map<String, dynamic>);
  }
}

main(List<String> args) {
  User user = User("huhx");
  changIt(user);
  print('after: ${user.name}'); // after: huhx
}

void changIt(User user) {
  User temp = user.clone();
  // User temp = user; then: after linux
  print('before: ${temp.name}'); // before: huhx
  temp.name = "linux";
}