C#的扩展方法

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Text.RegularExpressions;
using System.Linq;

namespace codeTest
{
class Program
{
static void Main(string[] args)
{
string str = "12312312 123123 123123";
Console.WriteLine(str.WordCount());
MyClass mylClass = new MyClass() { str = "123123123" };
Console.WriteLine(mylClass.WordCount());
Console.ReadLine();
}

}

/// <summary>
/// 扩展方法必须在静态类里面，扩展方法也必须是静态的，首参数为this
/// </summary>
public static class stringExtension
{
public static int WordCount(this string str)
{
return str.Count();
}

public static int WordCount(this MyClass mylClass)
{
return mylClass.str.Count();
}
}

public class MyClass
{
public string str;
}

}