dart_copy.dart

class Setter<T> {
  final T value;  
  
  Setter(this.value);
}

Setter<T> set<T>(T value) {
  return Setter<T>(value);
}

class Person {
  final String firstName;
  final String secondName;
  final int age;
  
  Person(this.firstName, this.secondName, this.age);
  
  Person copy({Setter<String> firstName, Setter<String> secondName, Setter<int> age}) {
    return Person(
       firstName?.value ?? this.firstName, 
       secondName?.value ?? this.secondName, 
       age?.value ?? this.age);
  }
  
  @override
  String toString() => "Person{ firstName=$firstName, secondName=$secondName, age=$age }";
}

void main() {  
  final person = Person("Dmytro", "Glynskyi", 30);
  final updatedPerson = person.copy(age: set(32));
  print(updatedPerson);
}

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