Question

似乎C＃中的扩展方法无法覆盖原始对象。这是为什么？例如：

using System;

namespace ExtensionTest
{
    public class MyTest {
        public string MyName { get; set; } 
    }


    class Program
   {
        static void Main(string[] args)
        {
            var myTest = new MyTest() { MyName = "Arne" };
            Console.WriteLine("My name is {0}", myTest.MyName);
            // Will write "My name is Arne"
            myTest.AlterMyTest();
            Console.WriteLine("My name is {0}", myTest.MyName);
            // Will write "My name is Bertil"
            myTest.OverwriteMyTest();
            Console.WriteLine("My name is {0}", myTest.MyName);
            // Will write "My name is Bertil" (why?)
        }
    }

    public static class ExtensionClass{
        public static void AlterMyTest(this MyTest myTest)
        {
            myTest.MyName = "Bertil";
        }

         public static void OverwriteMyTest(this MyTest myTest)
         {
             myTest = new MyTest() { MyName = "Carl" };
         }
    }
}

Answer 1

因为像往常一样，在传递给方法时会复制类的引用，并且您要将新对象分配给新引用。

对于非扩展方法，您可以通过ref/out关键字

传递引用

public static void Func(out MyClass b)
{
   b = new MyClass();
}

...
MyClass b;
Func(out b);
Assert.IsNotNull(b);

但是C＃编译器不允许ref与this一起使用（原因在于David Arno的评论）。您可以自由删除this关键字，并调用静态方法而不是扩展名。

为什么扩展方法不能覆盖原始对象？

1 个答案: