遅延評価

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

namespace Linqメソッドで遊ぶ
{
	class Program
	{
		static void Main(string[] args)
		{
			List<intheritHoge1> hoge1List = new List<intheritHoge1>();
			hoge1List.Add(new intheritHoge1() { a = "hoge1" });

			List<intheritHoge2> hoge2List = new List<intheritHoge2>();
			hoge2List.Add(new intheritHoge2() { a = "hoge2" });
			hoge2List.Add(new intheritHoge2() { a = "hoge1" });

			var union = hoge1List.Select(x => (Hoge)x).Union(hoge2List);
			if (true)
			{
				union = union.Where(x => x.a == "hoge2");
			}

			foreach (var item in union)
			{
				Console.WriteLine(item.a);
			}
			Console.Read();

		}
	}

	class Hoge
	{
		public string a = string.Empty;
	}

	class intheritHoge1 : Hoge
	{
	}

	class intheritHoge2 : Hoge
	{
	}
}