C#引用数据类型特点以及ref的使用

namespace ConsoleApplication6
{
    class Program
    {
        static void Main(string[] args)
        {
            Test1();
            Test2();
            Test3();
        }
        private static void Test1()
        {
            var a = new DataModel() { Value = 1 };
            var b = a;
            a = new DataModel() { Value = 2 };
            Console.WriteLine($"a = {a.Value}");
            Console.WriteLine($"b = {b.Value}");

            //Output: a=2 b=1
        }
        private static void Test2()
        {
            var a = new DataModel() { Value = 1 };
            ChangeVal(a);
            Console.WriteLine($"a = {a.Value}");
            //Output: a=1 b=1 c=2
        }
        private static void Test3()
        {
            var a = new DataModel() { Value = 1 };
            ChangeVal(ref a);
            Console.WriteLine($"a = {a.Value}");
            //Output: a=2 b=1 c=2
        }


        private static void ChangeVal(DataModel c)
        {
            var b = c;
            c = new DataModel() { Value = 2 };
            Console.WriteLine($"b = {b.Value}");
            Console.WriteLine($"c = {c.Value}");
        }

        private static void ChangeVal(ref DataModel c)
        {
            var b = c;
            c = new DataModel() { Value = 2 };
            Console.WriteLine($"b = {b.Value}");
            Console.WriteLine($"c = {c.Value}");
        }
    }

    public class DataModel
    {
        public int Value { get; set; }
    }
}