本文发表在 rolia.net 枫下论坛Boxing is an implicit conversion of a value type to the type object or to any interface type implemented by this value type. Boxing a value of a value allocates an object instance and copies the value into the new object.

Consider the following declaration of a value-type variable:

int i = 123;
The following statement implicitly applies the boxing operation on the variable i:

object o = i;
The result of this statement is creating an object o, on the stack, that references a value of the type int, on the heap. This value is a copy of the value-type value assigned to the variable i. The difference between the two variables, i and o, is illustrated in the following figure.

Boxing Conversion



It also possible, but never needed, to perform the boxing explicitly as in the following example:

int i = 123;
object o = (object) i;
Example
This example converts an integer variable i to an object o via boxing. Then the value stored in the variable i is changed from 123 to 456. The example shows that the object keeps the original copy of the contents, 123.

// boxing.cs
// Boxing an integer variable
using System;
class TestBoxing
{
public static void Main()
{
int i = 123;
object o = i; // Implicit boxing
i = 456; // Change the contents of i
Console.WriteLine("The value-type value = {0}", i);
Console.WriteLine("The object-type value = {0}", o);
}
}
Output
The value-type value = 456
The object-type value = 123更多精彩文章及讨论，请光临枫下论坛 rolia.net