如何在我的课堂上实现前后递增/递减运算符? [英] How to implement pre and post-increment / decrement operator in my class?

问题描述

我想重载++运算符，以便在我的c#类中使用运算符重载使用预递增和后递增.但是只有后增量有效.如何使这两个功能在我的课堂上都能正常工作? 假设我做了一个ABC类-

I want to overload ++ operator to use pre-increment and post-increment using operator overloading in my c# class. But only post-increment is working. How to make both function works in my class? Suppose I made a class ABC like -

using System;
using System.Collections.Generic;
using System.Text;

namespace Test
{
    class ABC
    {
      public int a,b;
      public ABC(int x, int y)
      {
        a = x;
        b = y;
      }
      public static ABC operator ++(ABC x)
      {
        x.a++;
        x.b++;
        return x;
      }
    }

    class Program
    {
        static void Main(string[] args)
        {
            ABC a = new ABC(5, 6);
            ABC b, c;
            b = a++;
            Console.WriteLine("After post increment values are {0} and {1} and values of b are {2} and {3}", a.a, a.b, b.a, b.b);// expected output a.a = 6, a.b = 7, b.a = 5, b.b = 6 but not get that
            c = ++a;
            Console.WriteLine("After pre increment values are {0} and {1} and values of c are {2} and {3}", a.a, a.b, c.a, c.b); // expected output a.a = 7, a.b = 7, c.a = 7, c.b = 8 works fine
            Console.Read();
        }
    }
}

推荐答案

您的示例无法正确实现此一元运算符，如 17.9.1一元运算符中的C#规范所指定:

Your sample fail to implement this unary operator correctly, as specified in the C# specification in 17.9.1 Unary operators :

与C ++不同，此方法不需要 并且事实上，不应修改 其操作数的值直接.

Unlike in C++, this method need not, and, in fact, should not, modify the value of its operand directly.

这是您的一些微单元测试样品:

Here is your sample with some micro unit tests :

using System;

class ABC
{
  public int a,b;
  public ABC(int x, int y)
  {
    a = x;
    b = y;
  }

  public static ABC operator ++(ABC x)
  {
    x.a++;
    x.b++;
    return x;
  }
}

class Program
{
    static void Main()
    {
        var a = new ABC(5, 6);
        if ((a.a != 5) || (a.b != 6)) Console.WriteLine(".ctor failed");

        var post = a++;
        if ((a.a != 6) || (a.b != 7)) Console.WriteLine("post incrementation failed");
        if ((post.a != 5) || (post.b != 6)) Console.WriteLine("post incrementation result failed");

        var pre = ++a;
        if ((a.a != 7) || (a.b != 8)) Console.WriteLine("pre incrementation failed");
        if ((pre.a != 7) || (pre.b != 8)) Console.WriteLine("pre incrementation result failed");

        Console.Read();
    }
}

您的代码失败是后递增结果，原因是您更改了作为参数传递的ABC实例，而不是返回新实例.更正的代码:

Your code fail is the post incrementation result and it is due to the fact that you alter the instance of ABC passed as parameter instead of returning a new instance. Corrected code :

class ABC
{
  public int a,b;
  public ABC(int x, int y)
  {
    a = x;
    b = y;
  }

  public static ABC operator ++(ABC x)
  {
    return new ABC(x.a + 1, x.b + 1);
  }
}

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