c#引用相等性比较（ReferenceEquals）

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Object.ReferenceEquals方法原型

public static bool ReferenceEquals(
object objA,
object objB
)

namespace TestReferenceEquality

    {

        struct TestStruct

        {

            public int Num { get; private set; }

            public string Name { get; private set; }

            public TestStruct(int i, string s) : this()

            {

                Num = i;

                Name = s;

            }

        }

        class TestClass

        {

            public int Num { get; set; }

            public string Name { get; set; }

        }

        class Program

        {

            static void Main()

            {

                //测试对象相等性

                #region ReferenceTypes

                // 创建具有两个相同值的引用实例。

                TestClass tcA = new TestClass() { Num = , Name = "New TestClass" };

                TestClass tcB = new TestClass() { Num = , Name = "New TestClass" };

                Console.WriteLine("ReferenceEquals(tcA, tcB) = {0}",

                                    Object.ReferenceEquals(tcA, tcB)); // false 

                // 赋值后, 引用同一对象 
                tcB = tcA;

                Console.WriteLine("After asignment: ReferenceEquals(tcA, tcB) = {0}",

                                    Object.ReferenceEquals(tcA, tcB)); // true

#endregion

                // 演示两个值类型实例从不具有引用相等性。
                #region ValueTypes

                TestStruct tsC = new TestStruct( , "TestStruct 1");

                //虽是拷贝，具有相同的值，但却不是同一对象，涉及装箱
                TestStruct tsD = tsC;

                Console.WriteLine("After asignment: ReferenceEquals(tsC, tsD) = {0}",

                                    Object.ReferenceEquals(tsC, tsD)); // false

                #endregion

                #region stringRefEquality

                //"Hello world!";常量字符串在内存中只有一份，所以两者指向同一内存 
                string strA = "Hello world!";

                string strB = "Hello world!";

                Console.WriteLine("ReferenceEquals(strA, strB) = {0}",

                                 Object.ReferenceEquals(strA, strB)); // true 

                // 改变引用用后，两者不再相等

                strA = "Goodbye world!";

                Console.WriteLine("strA = \"{0}\" strB = \"{1}\"", strA, strB);

                Console.WriteLine("After strA changes, ReferenceEquals(strA, strB) = {0}",

                                Object.ReferenceEquals(strA, strB)); // false 

                //string对象在运行期间被创建，跟strB是完全不同的两个对象，在用 Object.ReferenceEquals判断引用相等时则返回false
                StringBuilder sb = new StringBuilder("Hello world!");

                string stringC = sb.ToString();

                // False:

                Console.WriteLine("ReferenceEquals(stringC, strB) = {0}",

                                Object.ReferenceEquals(stringC, strB));

                // 字符串类重载了==运算符来执行相等比较
                Console.WriteLine("stringC == strB = {0}", stringC == strB); // true

                #endregion

            }

        }

    }