Immutability in Dart data classes is known as final

This class is immutable, why? After declaring the class you won't be able to change it's variables again.

class User {
  final String name;
  final int age;

  const User(this.name, this.age);
}

Bonus:

If you want the other methods that are normally included automatically in a language such as toMap, toJson, fromJson, fromMap , toString etc. You can also use code generation to get them with this extension:

https://marketplace.visualstudio.com/items?itemName=hzgood.dart-data-class-generator