4.4.2 空合并操作符让比较不再痛苦

    class Program
    {
        static void Main(string[] args)
        {
            Console.ReadKey();
        }
        static int Compare(Product x, Product y)
        {
            return PartialComparer.Compare(x.Name, y.Name) ?? PartialComparer.Compare(x.Age, y.Age) ?? PartialComparer.Compare(x.Popularity, y.Popularity) ?? 0;
        }
    }
    public class Product
    {
        public string Name { get; set; }
        public int Age { get; set; }
        public string Popularity { get; set; }
    }
    public static class PartialComparer
    {
        public static int? Compare<T>(T first, T second)
        {
            return Compare(Comparer<T>.Default, first, second);
        }
        public static int? Compare<T>(IComparer<T> compare, T first, T second)
        {
            int ret = compare.Compare(first, second);
            return ret == 0 ? new int?() : ret;
        }
        public static int? ReferenceCompare<T>(T first, T second) where T : class
        {
            return first == second ? 0 : first == null ? -1 : second == null ? 1 : new int?();
        }
    }