C#重载运算符详解

2020-01-24 02:29:36

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本文较为详细的描述了重载运算符的方法。一般来说，重载运算符在实际的项目开发中会经常的用到，但如果某些自定义类型通过简短几行代码重载一些常用的运算符（如：+-*/），就能让编程工作带来方便；重载运算符就是告诉编译器+-*/等运算符对于自定义类型进行什么样的操作，在代码中需要注意几点。

一、尽可能的不要改变运算符本身的含义

二、所有的运算符重载都必须声明为public和static

三、不同于扩展方法，所重载的方法必须是在被重载的类型内部，且用关键字operator

C#中的两个字符串相加，实际上是连接两个字符串，假如有两个EmployeeDetail类型相加得到一个EmployeeCollection集合，如：

EmployeeDetail a,b;....EmployeeCollection collection = a+b;

当编译器遇到上面的代码时就会自动调用EmployeeDetail类上标有operator +的静态方法，并将两个操作数a和b作为参数传递给对于的方法，该方法需要方法一个值赋给collection，假设EmployeeDetail类有三个属性分别是FirstName,MiddleName,LastName，还重写了ToString方法返回一个连接这三个名称的字符串，代码如：

[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();   } }

下面的代码为“+”运算符提供支持的运算符重载：

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

OK，给EmployeeDetail类加上这样的一个方法之后，我们就可以像下面那个写代码了：

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

但是这样还不够完美，假设a，b，c都是EmployeeDetail类型，下面的代码会抛出一个编译错误：

EmployeeCollection collection = a + b + c;

为什么编译不通过呢？大家都知道除了赋值运算符外表达式是从左到右执行的，a+b返回的是EmployeeCollection类型，EmployeeCollection类型并没有重载“+”运算符，编译器不知道要执行什么操作，所以我们还有下面的两个方法：

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

这看起来似乎已经很完美了，但我们还可以做得更好一些，比如要将字符串“Jackson.Bruce”直接隐式转换为EmployeeDetail类型，也就是说可以将“Jackson.Bruce"这种格式的字符串直接赋给EmployeeDetail类型的对象，如：EmployeeDetail employee= “Jackson.Bruce"，那么就需要重载隐式类型转换运算符了，代码如下：

/// <summary>/// 隐式类型转换/// </summary>/// <param name="name"></param>/// <returns></returns>public static implicit operator EmployeeDetail(string name){　　　　　　　/// 其实在这里可以写一个正则表达式检查name的字符串格式是否合法，如果不合法就抛出异常　　　　　　　///  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 };}

看到这里您是不是迫不及待地想试试看，OK写个控制台程序来测试一下：

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();}

运行结果如下图所示：

全部代码，里面还包含其他运算符的重载，这里就不再介绍了，赶紧动手测试一下吧：

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace 重载运算符{  [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>    /// 隐式类型转换    /// </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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