.net 3.5 新功能重写ToInt()方法

public static class ExtensionString
{
public static int ToInt(this string str)
    {
        int ret = 0;
        if (str != null && str.Length > 0)
        {
            str = str.Replace(",", string.Empty);
            int.TryParse(str, out ret);
        }
        return ret;
    }
}

public static int ToInt(this string str) //this 关键字的作用.