using System.Collections.Generic;

using System;

using System.Linq;

​

​

class Something

{

    public bool OkState()

    {

        Console.WriteLine("heavy state calculation");

        return true;

    }

}

​

public class Program

{

    public static void Main()

    {

        var something = new Something();

        var oriList = new List<Something>();

        oriList.Add(something);

        oriList.Add(something);

        var enumerable = oriList.Where(o => o.OkState());

        foreach(var s in enumerable){

        }

        foreach(var s in enumerable){

        }               

    }

}