C#|装箱拆箱

原文:https://www.geeksforgeeks.org/c-sharp-boxing-unboxing/

前提条件:c# 中的数据类型

拳击和拆箱是【c#中的一个重要概念。C# Type 系统包含 三种数据类型 : 值类型(int、char 等)、引用类型(object) 和指针类型。基本上，它将值类型转换为引用类型，反之亦然。装箱和取消装箱实现了类型系统的统一视图，其中任何类型的值都可以被视为对象。

c# 打拳

• 转换一个 值类型(字符，整型等)的过程。)到一个参考型(物体)叫做拳。


• 装箱是使用对象类型(超类型)的隐式转换过程。


• 值类型始终存储在堆栈中。引用的类型存储在堆中。



• 例:

  ```cs
  int num = 23; // 23 will assigned to num
  Object Obj = num; // Boxing

  ```




• Description : First declare a value type variable (num), which is integer type and assigned it with value 23. Now create a references object type (obj) and applied Explicit operation which results in num value type to be copied and stored in object reference type obj as shown in below figure :




• 让我们用 C# 编程代码来理解拳击:

  ```cs
  // C# implementation to demonstrate
  // the Boxing
  using System;
  class GFG {

  // Main Method
      static public void Main()
      {

  // assigned int value
          // 2020 to num
          int num = 2020;

  // boxing
          object obj = num;

  // value of num to be change
          num = 100;

  System.Console.WriteLine
          ("Value - type value of num is : {0}", num);
          System.Console.WriteLine
          ("Object - type value of obj is : {0}", obj);
      }
  }
  ```

  输出:

  ```cs
  Value - type value of num is : 100
  Object - type value of obj is : 2020

  ```

在 C# 中脱氧

• 将 参考类型转换为值类型 的过程称为拆箱。


• 它是显式的转换过程。



• 例:

  ```cs
  int num = 23; // value type is int and assigned value 23
  Object Obj = num; // Boxing
  int i = (int)Obj; // Unboxing

  ```




• Description : Declaration a value type variable (num), which is integer type and assigned with integer value 23. Now, create a reference object type (obj).The explicit operation for boxing create an value type integer i and applied casting method. Then the referenced type residing on Heap is copy to stack as shown in below figure :




• 让我们来理解用 C# 编程代码打开的锁:

  ```cs
  // C# implementation to demonstrate
  // the Unboxing
  using System;
  class GFG {

  // Main Method
      static public void Main()
      {

  // assigned int value
          // 23 to num
          int num = 23;

  // boxing
          object obj = num;

  // unboxing
          int i = (int)obj;

  // Display result
          Console.WriteLine("Value of ob object is : " + obj);
          Console.WriteLine("Value of i is : " + i);
      }
  }
  ```

  输出:

  ```cs
  Value of ob object is : 23
  Value of i is : 23

  ```