C#重載運(yùn)算符詳解

更新時(shí)間：2014年08月25日 08:54:14 投稿：shichen2014

這篇文章主要介紹了C#重載運(yùn)算符,是進(jìn)行C#程序設(shè)計(jì)中非常重要的一個(gè)技巧,需要的朋友可以參考下

本文較為詳細(xì)的描述了重載運(yùn)算符的方法。一般來說，重載運(yùn)算符在實(shí)際的項(xiàng)目開發(fā)中會(huì)經(jīng)常的用到，但如果某些自定義類型通過簡(jiǎn)短幾行代碼重載一些常用的運(yùn)算符（如：+-*/），就能讓編程工作帶來方便；重載運(yùn)算符就是告訴編譯器+-*/等運(yùn)算符對(duì)于自定義類型進(jìn)行什么樣的操作，在代碼中需要注意幾點(diǎn)。

一、盡可能的不要改變運(yùn)算符本身的含義

二、所有的運(yùn)算符重載都必須聲明為public和static

三、不同于擴(kuò)展方法，所重載的方法必須是在被重載的類型內(nèi)部，且用關(guān)鍵字operator

C#中的兩個(gè)字符串相加，實(shí)際上是連接兩個(gè)字符串，假如有兩個(gè)EmployeeDetail類型相加得到一個(gè)EmployeeCollection集合，如：

EmployeeDetail a,b;

....

EmployeeCollection collection = a+b;

當(dāng)編譯器遇到上面的代碼時(shí)就會(huì)自動(dòng)調(diào)用EmployeeDetail類上標(biāo)有operator +的靜態(tài)方法，并將兩個(gè)操作數(shù)a和b作為參數(shù)傳遞給對(duì)于的方法，該方法需要方法一個(gè)值賦給collection，假設(shè)EmployeeDetail類有三個(gè)屬性分別是FirstName,MiddleName,LastName，還重寫了ToString方法返回一個(gè)連接這三個(gè)名稱的字符串，代碼如：

[Serializable]
 public class EmployeeDetail
 {
   public string FirstName { get; set; }
   public string MiddleName { get; set; }
   public string LastName { set;get; }
   public override string ToString()
   {
     return string.Format("{0}{1}{2}{3}{4}", FirstName, string.IsNullOrWhiteSpace(MiddleName) ? null : "."
       , MiddleName
       , string.IsNullOrWhiteSpace(LastName) ? null : ".",
       LastName).Trim();
   }
 }

下面的代碼為“+”運(yùn)算符提供支持的運(yùn)算符重載：

public static EmployeeCollection operator +(EmployeeDetail a, EmployeeDetail b)
{
  return new EmployeeCollection() { a, b };
}

OK，給EmployeeDetail類加上這樣的一個(gè)方法之后，我們就可以像下面那個(gè)寫代碼了：

EmployeeCollection collection = new EmployeeDetail(){FirstName="Jackson",LastName="Bruce"} + new EmployeeDetail(){FirstName="Michael",LastName="Jackson"} ;

但是這樣還不夠完美，假設(shè)a，b，c都是EmployeeDetail類型，下面的代碼會(huì)拋出一個(gè)編譯錯(cuò)誤：

EmployeeCollection collection = a + b + c;

為什么編譯不通過呢？大家都知道除了賦值運(yùn)算符外表達(dá)式是從左到右執(zhí)行的，a+b返回的是EmployeeCollection類型，EmployeeCollection類型并沒有重載“+”運(yùn)算符，編譯器不知道要執(zhí)行什么操作，所以我們還有下面的兩個(gè)方法：

public static EmployeeCollection operator +(EmployeeCollection collection, EmployeeDetail a)
{
  collection.Add(a);
  return collection;
}
public static EmployeeCollection operator +(EmployeeDetail a, EmployeeCollection collection)
{
  return collection + a;
}

這看起來似乎已經(jīng)很完美了，但我們還可以做得更好一些，比如要將字符串“Jackson.Bruce”直接隱式轉(zhuǎn)換為EmployeeDetail類型，也就是說可以將“Jackson.Bruce"這種格式的字符串直接賦給EmployeeDetail類型的對(duì)象，如：EmployeeDetail employee= “Jackson.Bruce"，那么就需要重載隱式類型轉(zhuǎn)換運(yùn)算符了，代碼如下：

/// <summary>
/// 隱式類型轉(zhuǎn)換
/// </summary>
/// <param name="name"></param>
/// <returns></returns>
public static implicit operator EmployeeDetail(string name)
{
　　　　　　　/// 其實(shí)在這里可以寫一個(gè)正則表達(dá)式檢查name的字符串格式是否合法，如果不合法就拋出異常
　　　　　　　///
  string[] arr;
  return string.IsNullOrWhiteSpace(name) ? null :
 new EmployeeDetail()
 {
   FirstName = (arr = name.Trim().Split('.'))[0]
   ,
   LastName = arr.Length > 1 ? arr[arr.Length > 2 ? 2 : 1] : null,
   MiddleName = arr.Length > 2 ? arr[1] : null
 };
}
public static EmployeeCollection operator +(EmployeeDetail a, string b)
{
  return new EmployeeCollection() { a, b };
}

看到這里您是不是迫不及待地想試試看，OK寫個(gè)控制臺(tái)程序來測(cè)試一下：

static void Main(string[] args)
{
  EmployeeDetail employee = "Jackson.Bruce";
  Console.WriteLine("FirstName={0},MiddleNam={1},LastName={2}", employee.FirstName, employee.MiddleName, employee.LastName);
  Console.WriteLine("toString={0}", employee);
  Console.WriteLine();

  EmployeeCollection collection = "Michael.Jackson" + employee;

  collection += "Bruce.Lee";
  foreach (var e in collection)
  {
 Console.WriteLine(e);
  }
  Console.WriteLine();

  collection -= employee;

  foreach (var e in collection)
  {
 Console.WriteLine(e);
  }
  Console.WriteLine("===end===");
  Console.Read();
}

運(yùn)行結(jié)果如下圖所示：

全部代碼，里面還包含其他運(yùn)算符的重載，這里就不再介紹了，趕緊動(dòng)手測(cè)試一下吧：

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

namespace 重載運(yùn)算符
{
  [Serializable]
  public class EmployeeDetail
  {
    public string FirstName { get; set; }
    public string MiddleName { get; set; }
    public string LastName { set;get; }
    public static EmployeeCollection operator +(EmployeeDetail a, EmployeeDetail b)
    {
      return new EmployeeCollection() { a, b };
    }

   
    
    public static EmployeeCollection operator +(EmployeeCollection collection, EmployeeDetail a)
    {
      collection.Add(a);
      return collection;
    }
    public static EmployeeCollection operator +(EmployeeDetail a, EmployeeCollection collection)
    {
      return collection + a;
    }
    /// <summary>
    /// 隱式類型轉(zhuǎn)換
    /// </summary>
    /// <param name="name"></param>
    /// <returns></returns>
    public static implicit operator EmployeeDetail(string name)
    {
      string[] arr;
      return string.IsNullOrWhiteSpace(name) ? null :
        new EmployeeDetail()
        {
          FirstName = (arr = name.Trim().Split('.'))[0]
          ,
          LastName = arr.Length > 1 ? arr[arr.Length > 2 ? 2 : 1] : null,
          MiddleName = arr.Length > 2 ? arr[1] : null
        };
    }
    public static EmployeeCollection operator +(EmployeeDetail a, string b)
    {
      return new EmployeeCollection() { a, b };
    }
    public override string ToString()
    {
      return string.Format("{0}{1}{2}{3}{4}", FirstName, string.IsNullOrWhiteSpace(MiddleName) ? null : "."
        , MiddleName
        , string.IsNullOrWhiteSpace(LastName) ? null : ".",
        LastName).Trim();
    }
  }
  public class EmployeeCollection : List<EmployeeDetail>
  {
    public static EmployeeCollection operator +(EmployeeCollection a, string b)
    {
      a.Add(b);
      return a;
    }
    public static EmployeeCollection operator +(string b, EmployeeCollection a)
    {
      return a + b;
    }

    public static EmployeeCollection operator -(EmployeeCollection a, EmployeeDetail b)
    {
      a.Remove(b);
      return a;
    }
  }

  class Program
  {
    static void Main(string[] args)
    {
      EmployeeDetail employee = "Jackson.Bruce";
      Console.WriteLine("FirstName={0},MiddleNam={1},LastName={2}", employee.FirstName, employee.MiddleName, employee.LastName);
      Console.WriteLine("toString={0}", employee);
      Console.WriteLine();

      EmployeeCollection collection = "Michael.Jackson" + employee;

      collection += "Bruce.Lee";
      foreach (var e in collection)
      {
        Console.WriteLine(e);
      }
      Console.WriteLine();

      collection -= employee;

      foreach (var e in collection)
      {
        Console.WriteLine(e);
      }


      Console.WriteLine("===end===");
      Console.Read();
    }
  }
}

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