继承List<T>

1、SPList

    class SPList<T> : List<T>
    {
        public decimal Average(Func<T, decimal> s)
        {
            var list = (List<T>)this;
            decimal price = list.Average(s) * decimal.Parse("0.8");
            return price;
        }
    }

2、model

    public class ProductSet
    {
        public int ID { get; set; }

        public string Name { get; set; }

        public int CategoryID { get; set; }

        public decimal Price { get; set; }
    }

3、执行

            SPList<ProductSet> products = new SPList<ProductSet>() {
                new ProductSet{ ID = 10000, Name= "BOOKKX01", Price= 90,CategoryID=0},
                new ProductSet{ ID = 10001, Name= "BOOKKX02", Price= 70,CategoryID=0},
                new ProductSet{ ID = 10002, Name= "BOOKKX03", Price= 80,CategoryID=0}
            };
            Console.WriteLine(products.Average(p=>p.Price));   // 64
            Console.WriteLine(products.AsEnumerable().Average(p => p.Price)); // 80