Constructors in Dart

main.dart

// Constructors in Dart (as of v2.5)

// This example can be run at https://dartpad.dartlang.org/fc100517efced76881fd0d8d37f673a8
// For other examples see https://gist.github.com/kirkdrichardson

void main() {
  // Use the default constructor
  final Car c = Car();
  print('Car with default constructor id: ${c.id}');
  print('\n\n');
  
  // Use the parameterized constructor
  final CarParam cp = CarParam(42);
  print('Car with parameterized constructor id: ${cp.id}');
    print('');
  
  // Use the named constructor
  final CarParam cNamed = CarParam.myNamedConstructor(99, 'Toyota');
  print('Car with named constructor id: ${cNamed.id} AND... name: ${cNamed.name}');
}

// Default constructor
class Car {
  int id;

  Car() {
    print('Ran default constructor');
  }
  
  // 🚫Expect Error --> "The default constructor is already defined."
  // You can only have EITHER the default or a parameterized constructor. 🤯
  // For multiple constructors, see named constructor usage below. 🙌
//   Car(id) {
//     this.id = id;
//   }
}

class CarParam {
  int id;
  String name;
  
  // Paramaterized constructor.
  CarParam(int id) {
    print('Ran paramaterized constructor.');
    this.id = id;
  }
  
  // To have multiple constructors, we can use named constructors, e.g.
  CarParam.myNamedConstructor(int id, String name){
    print('Ran named constructor.');
    this.id = id;
    this.name = name;
  }
}