电话号码 马赛克*号 string类扩展

        /// <summary>

        /// 字符串马赛克

        /// </summary>

        /// <param name="source"></param>

        /// <param name="mask">马赛克</param>

        /// <param name="left">左边长度</param>

        /// <param name="length">打码长度</param>

        /// <returns></returns>

        public static string ToMask(this string source, char mask, int left, int length)

        {

            if (source.IsNullOrEmpty())

            {

                return source;

            }

            var pattern = string.Format(@"(?<=^.{{{0}}}).{{{1}}}", left, length);

            return Regex.Replace(source, pattern, mask.Pad(length));

        }

string类扩张 ，可运用于电话号码打* 号