重載運算符

重載運算符在實際的工做中很用到，但若是某些自定義類型經過簡短几行代碼重載一些經常使用的運算符（如：+-*/），就能讓編程工做帶來方便；重載運算符就是告訴編譯器+-*/等運算符對於自定義類型進行什麼樣的操做，在代碼中須要注意幾點。

1、儘量的不要改變運算符自己的含義

2、全部的運算符重載都必須聲明爲public和static

3、不一樣於擴展方法，所重載的方法必須是在被重載的類型內部，且用關鍵 operator

C#中的兩個字符串相加，其實是鏈接兩個字符串，假若有兩個EmployeeDetail類型相加獲得一個EmployeeCollection集合，如：

EmployeeDetail a,b;

....

EmployeeCollection collection = a+b;

當編譯器遇到上面的代碼時就會自動調用EmployeeDetail類上標有operator +的靜態方法，並將兩個操做數a和b做爲參數傳遞給對於的方法，該方法須要方法一個值賦給collection，假設EmployeeDetail類有三個屬性分別是FirstName,MiddleName,LastName，還重寫了ToString方法返回一個鏈接這三個名稱的字符串，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();
        }
    }

 

下面的代碼爲「+」運算符提供支持的運算符重載：

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

OK，給EmployeeDetail類加上這樣的一個方法以後，咱們就能夠像下面那個寫代碼了：

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

可是這樣還不夠完美，假設a，b，c都是EmployeeDetail類型，下面的代碼會拋出一個編譯錯誤：

EmployeeCollection collection = a + b + c;

爲何編譯不經過呢？你們都知道除了賦值運算符外表達式是從左到右執行的，a+b返回的是EmployeeCollection類型，EmployeeCollection類型並無重載「+」運算符，編譯器不知道要執行什麼操做，因此咱們還有下面的兩個方法：

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

 

 

這看起來彷佛已經很完美了，但咱們還能夠作得更好一些，好比要將字符串「Jackson.Bruce」直接隱式轉換爲EmployeeDetail類型，也就是說能夠將「Jackson.Bruce"這種格式的字符串直接賦給EmployeeDetail類型的對象，如：EmployeeDetail employee= 「Jackson.Bruce"，那麼就須要重載隱式類型轉換運算符了，代碼以下：

/// <summary>
        /// 隱式類型轉換
        /// </summary>
        /// <param name="name"></param>
        /// <returns></returns>
        public static implicit operator EmployeeDetail(string name)
        {

　　　　　　　/// 其實在這裏能夠寫一個正則表達式檢查name的字符串格式是否合法，若是不合法就拋出異常
　　　　　　　///
            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 };
        }

 

 

看到這裏您是否是火燒眉毛地想試試看，OK寫個控制檯程序來測試一下：

        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();
        }

 

 

運行結果

 

 

所有代碼，裏面還包含其餘運算符的重載，這裏就再也不介紹了，趕忙試試吧：

 

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

namespace 重載運算符
{
    [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();
        }
    }
}