safaribook-pro-aspnet-mvc3/chap5_essential_language_features/essential_csharp_features/Program.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using automatically_implemented_properties;

namespace automatically_implemented_properties
{
    class Program
    {
        static void Main(string[] args)
        {
            // create and populate Shopping Cart, implementing IEnumerable<Product> interface
            IEnumerable<Product> products = new ShoppingCart
            {
                Products = new List<Product>
                {
                    new Product {Name = "Kayak", Category = "Watersports", Price = 275M},
                    new Product {Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                    new Product {Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                    new Product {Name = "Corner flag", Category = "Soccer", Price = 34.95M}
                }
            };
            
            Func<Product, bool> categoryFilter = delegate(Product prod)
            {
                return prod.Category == "Soccer";
            };

            IEnumerable<Product> filteredProducts = products.Filter(categoryFilter);
            
            foreach (Product prod in filteredProducts) 
            {
                Console.WriteLine("Name: {0}, Price {1:c}", prod.Name, prod.Price);
            }

            decimal total = products.FilterByCategory("Soccer").TotalPrices();
            Console.WriteLine("Filtered total: {0:c}", total);
        }

    }

    public static class MyExtensionMethod
    {
        public static decimal TotalPrices(this IEnumerable<Product> productEnum)
        {
            decimal total = 0;
            foreach (Product prod in productEnum)
            {
                total += prod.Price;
            }
            return total;
        }

        public static IEnumerable<Product> FilterByCategory(this IEnumerable<Product> productEnum,
                                                            string categoryParam)
        {
            foreach (Product prod in productEnum)
            {
                if (prod.Category == categoryParam)
                {
                    yield return prod;
                }
            }
        }

        public static IEnumerable<Product> Filter(this IEnumerable<Product> productEnum,
            Func<Product, bool> selectorParam)
        {
            foreach (Product prod in productEnum)
            {
                if (selectorParam(prod))
                {
                    yield return prod;
                }
            }
        }
    }
}