关于var1=var2=something赋值语句的思考

刚才在阅读《c#本质论》一书时，开头有提到var1=var2=something的赋值体，之前也曾用过（但是个人不建议这么使用），但是没有认真思考这种赋值方式的本质问题，即：var1是对var2的引用还是对something的引用。后面我编写了一些PoC代码对此进行验证。

代码片段1：

            #region TestString
            string str1, str2;
            //str1 = str2 = "This is a test string...";
            str2 = "This is a test string...";
            str1 = str2;
            Console.WriteLine("Str1: " + str1);
            Console.WriteLine("Str2: " + str2);
            str2 = "This is another test string...";
            Console.WriteLine();
            Console.WriteLine("Str1: " + str1);
            Console.WriteLine("Str2: " + str2);
            #endregion

 输出的结果是：

Str1: This is a test string...
Str2: This is a test string...

Str1: This is a test string...
Str2: This is another test string...

还是

Str1: This is a test string...
Str2: This is a test string...
Str1: This is another test string...
Str2: This is another test string...

呢？

测试答案是前者。

 

再看看片段2：

class Program
    {
        static void Main(string[] args)
        {
            #region TestObject
            ObjectToTest ott1, ott2;
            //ott1 = ott2 = new ObjectToTest(100);
            ott2 = new ObjectToTest(100);
            ott1 = ott2;
            Console.WriteLine("OTT1: " + ott1.Num);
            Console.WriteLine("OTT2: " + ott2.Num);

            ott2 = new ObjectToTest(150);
            Console.WriteLine("OTT1: " + ott1.Num);
            Console.WriteLine("OTT2: " + ott2.Num); 
            #endregion

            Console.Read();
        }
    }

    class ObjectToTest
    {
        int num;
        public int Num
        {
            get { return num; }
            set { num = value; }
        }

        public ObjectToTest(int num)
        {
            Num = num;
        }
    }

 

输出结果又是如何呢？这里的ott1和ott2都是对象，也就是涉及到引用传递的问题了。我们记new ObjectToTest(100)为obj1， new ObjectToTest(150)为obj2.则在语句ott1=ott2执行后，ott1是对ott2的引用，还是对obj1的引用呢？在后面当ott2=new ObjectToTest(150)执行后，ott1是对obj1的引用还是对obj2的引用呢？

 

执行代码，观看结果为：

OTT1: 100
OTT2: 100
OTT1: 100
OTT2: 150

可知，这里的ott1只是对obj1的引用，而非obj2的引用。