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

namespace LinqDemo.AIndex
{
    internal class AIndex
    {
        public static void Start()
        {
            foreach (var str in GetStrings())
                Console.WriteLine(str);

            Console.WriteLine("\n");
            var res = GetStrings().CWhere(c => c.Length < 4);
            foreach (var item in res)
                Console.WriteLine(item);

            Console.WriteLine("\n");
            var secRes = GetStrings().CWhere<string>(c => c.Length > 4);
            foreach (var item in secRes)
                Console.WriteLine(item);
        }

        static IEnumerable<string> GetStrings()
        {
            yield return "hello";
            yield return "mxl";
            yield return "atman.wiki";
        }
    }

    internal static class Extend{
        internal static IEnumerable<string> CWhere(this IEnumerable<string> enums, Func<string, bool> func)
        {
            foreach (var item in enums)
            {
                if (func(item))
                    yield return item;
            }
        }

        internal static IEnumerable<T> CWhere<T>(this IEnumerable<T> enums, Func<T, bool> func)
        {
            foreach (var item in enums)
            {
                if (func(item))
                    yield return item;
            }
        }
    }
}