c# – 扩展方法(类)或访问者模式

哪个更容易设计,什么时候应该使用扩展方法而不是访问者模式和反面？

除了语法糖以帮助程序可读性之外,是否有任何合理的理由在访问者类上使用扩展方法？

您将如何设计包含扩展方法的系统,您会将它们分类为UML图吗？

namespace ExtensionMethods
{
    public static class MyExtensions
    {
        public static int WordCount(this String str)
        {
            return str.Split(new char[] { ' ','.','?' },StringSplitOptions.RemoveEmptyEntries).Length;
        }
    }   
}

我可能有错误的模式,它看起来像上面代码中的访问者模式.所以我认为我的比较成立了.

有些代码,我会说扩展方法看起来像访问者模式.

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

namespace ConsoleApplication1
{
    #region Interfaces

    public interface IFred
    {
        string Data
        {
            get;
            set;
        }        

        string doSomething();
    }


    public interface IBob
    {
        string Data
        {
            get;
            set;
        }
    }

    #endregion

    #region fred stuff

    public partial class Fred : IFred
    {

        public string doSomething()
        {
            return this.Data + " is really cool";
        }

        public string Value()
        {
            throw new NotImplementedException();
        }

    }

    public partial class Fred
    {
        public string Data
        {
            get;
            set;
        }
    }

    #endregion


    #region bob stuff

    public class BobData : IBob
    {
        public string Data
        {
            get;
            set;
        }
    }

    public class BobData2 : IBob
    {
        private string pData;
        public string Data
        {

            get
            {
                return pData + " and then some!";
            }
            set
            {
                pData = value;
            }
        }
    }

    public class BobVisitor
    {
        public string dosomething(IBob bobData)
        {
            Console.WriteLine(bobData.Data);
            return "ok";
        }

        public string dosomethingOnlyToBob(BobData bobData)
        {
            Console.WriteLine("hello bob version 1");
            return "ok";
        }


        public string dosomethingOnlyToBob2(BobData2 bobData)
        {
            Console.WriteLine("hello bob version 2");
            return "ok";
        }

    }

    #endregion


    public static class Visitor
    {
        public static string visit(this IBob bobObj)
        {
            Console.WriteLine(bobObj.Data);
            return "ok";

        }

        public static string visit(this IFred fredObj)
        {
            Console.WriteLine(fredObj.Data);
            return "ok";
        }
    }


    class Program
    {
        static void Main(string[] args)
        {

            //Another way of abstracting methods from data,using Partial Classes.
            var fredObj = new Fred();
            fredObj.Data = "fred data";
            fredObj.doSomething();


            //Create the bob classes version 1 and 2
            var bobObj = new BobData();
            bobObj.Data = "bob data";

            var bob2Obj = new BobData2();
            bob2Obj.Data = "bob 2 data";


            //using the bobVisitor Class
            var bobVisitor = new BobVisitor();

            bobVisitor.dosomething(bobObj);
            bobVisitor.dosomething(bob2Obj);

            bobVisitor.dosomethingOnlyToBob(bobObj);
            bobVisitor.dosomethingOnlyToBob2(bob2Obj);


            //using the extension methods in the extension class
            bobObj.visit();
            fredObj.visit();

            Console.Read();
        }
    }
}