main.dart

class Color {
  Color(this.name);
  String name;
  
  String toString() {
    return 'Color:${this.name}';
  }
}

class ColorHolder {
  Color? _cache;
  void create() {
    if (_cache == null) {
      _cache = Color("black");
    } else {
      _cache = Color("red");
    }
    
  }
  Color? get() {
    return _cache;
  }
}


void main() {
  final holder = ColorHolder();
  final c1 = holder.get();
  print(c1);
  
  print('\n create \n');
  holder.create();
  
  final c2 = holder.get();
  print('c1: $c1');
  print('c2: $c2');
  
  print('\n create \n');
  holder.create();
  
  print('c1: $c1');
  print('c2: $c2');
}