使用迭代器 遍历文件信息的详解

        public static ienumerable<string> readlines(string filename)
        {
            using (textreader reader = file.opentext(filename))
            {
                string line;
                if ((line = reader.readline()) != null)
                {
                    yield return line;
                }
            }
        }
        static void main()
        {
            foreach (string line in iterator.readlines(""))
            {
                console.writeline(line);
            }
        }

       public static ienumerable<t> where<t>(ienumerable<t> source, predicate<t> predicate)
        {
            if (source == null || predicate == null)
            {
                throw new argumentnullexception();
            }
            return whereimplemeter(source, predicate);
        }
       private static ienumerable<t> whereimplemeter<t>(ienumerable<t> source, predicate<t> predicate)
        {
            foreach (t item in source)
            {
                if (predicate(item))
                {
                    yield return item;
                }
            }
        }
        static void main()
        {
            ienumerable<string> lines = file.readalllines(@"your file name");
            predicate<string> predicate = delegate(string line)
            {
                return line.startswith("using");
            };
            foreach (string str in where(lines, predicate))
            {
                console.writeline(str);
            }

        }