Dart playground

test.dart

class Person {
  String _name;
  int _age;
  int money;

  Person(this._name, this._age, this.money);

  Person.named({String name, int age = 25}) {
    this._name = name;
    this._age = age;
    this.money = 0;
  }

  Person.newBorn(String name) {
    this._name = name;
    this._age = 0;
    this.money = 0;
  }

  String get name {
    return this._name;
  }
  
  set name (String name) {
    this._name = name;
  }
  
  int get age {
    return this._age;
  }

  set age(int age) {
    if (age >= 0 && age <= 105) {
      this._age = age;
    } else {
      this._age = 0;
    }
  }
}

class Dog {
  String _name;
  String _sound;
  Person _owner;
  
  Dog(this._name, this._sound, this._owner);
  
  @override
  String toString() {
    return '{name: ${this._name}, owner: ${this._owner._name}}';
  } 
  
}

double addNumbers(double num1, double num2) {
  return num1 + num2;
}

void printPerson(Person p) {
  print('{name: ${p._name}, age: ${p._age}}, money: ${p.money}}');
}

void main() {
  var p1 = Person.named(name: 'Felipe', age: 30);
  var baby = Person.newBorn('Enzo');
  var p2 = Person('Xaxu', 26, 0);
  printPerson(p1);
  printPerson(p2);
  printPerson(baby);
  
  p1.money = 200;
  printPerson(p1);
  
  // We made this to prove that we can access the private value from person inside the same file
  var doge = Dog('Filó', 'au au', p1);
  print(doge);
}