扩展方法

    class Program
    {
        static void Main(string[] args)
        {
            //扩展方法 语法糖 谨慎使用
            int[] ints = { 10, 45, 15, 39, 21, 26 };
            var result = ints.OrderBy(g => g);

            foreach (int v in result)
            {
                Console.WriteLine(v);
            }
            string s = "This is Jikexueyuan c# tutorial";
            Console.WriteLine("the string have {0} words", s.wordCount());
            Console.ReadLine();
        }
    }
    public static class StringExtension
    {
        public static int wordCount(this string Str)
        {
            return Str.Split(new char[] { ' ', ',', '.', '!' }, StringSplitOptions.RemoveEmptyEntries).Length;
        }
    }

枚举上的实现

public enum Grades { F = 0, D = 1, C = 2, B = 3, A = 4 };
    class Program
    {

        static void Main(string[] args)
        {
            var g1 = Grades.D;
            var g2 = Grades.F;
            var g3 = Grades.A;
            Console.WriteLine("1 {0} a passing grade", g1.Passing() ? "is" : "is not");
            Console.WriteLine("2 {0} a passing grade", g2.Passing() ? "is" : "is not");
            Console.WriteLine("3 {0} a passing grade", g3.Passing() ? "is" : "is not");
            EnumExtension.miniPassing = Grades.C;
            Console.WriteLine("1 {0} a passing grade", g1.Passing() ? "is" : "is not");
            Console.WriteLine("2 {0} a passing grade", g2.Passing() ? "is" : "is not");
            Console.WriteLine("3 {0} a passing grade", g3.Passing() ? "is" : "is not");
            Console.ReadLine();
        }
    }
    public static class EnumExtension
    {
        public static Grades miniPassing = Grades.D;
        public static bool Passing(this Grades grades)
        {
            return grades >= miniPassing;
        }
    }