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重载运算符

时间:2014-06-25 11:37:32      阅读:214      评论:0      收藏:0      [点我收藏+]

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重载运算符在实际的工作中很用到,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 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

 

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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,赶紧试试吧:

 

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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重载运算符

标签:des   style   class   blog   code   ext   

原文地址:http://www.cnblogs.com/Jackson-Bruce/p/3807246.html

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