static void Main(string[] args) { var apple = new Product("Apple", Color.Green, Size.Small); var tree = new Product("Tree", Color.Green, Size.Large); var house = new Product("House", Color.Blue, Size.Large); Product[] products = { apple, tree, house }; var pf = new ProductFilter(); Console.WriteLine("Green products(old): "); foreach (var p in pf.FilterByColor(products, Color.Green)) { Console.WriteLine($" - {p.Name} is green."); } var bf = new BetterFilter(); Console.WriteLine("Green product (new) :"); foreach (var p in bf.Filter(products, new ColorSpecification(Color.Green))) { Console.WriteLine($" - {p.Name} is green."); } Console.WriteLine("Large blue items"); foreach (var p in bf.Filter( products, new AndSpecification <Product>( new ColorSpecification(Color.Blue), new SizeSpecification(Size.Large) ))) { Console.WriteLine($" - {p.Name} is big and blue."); } Console.ReadKey(); }