using System;
using System.Linq;
using System.Collections.Generic;
 
public class Test
{
        private static bool veryExpensiveMethod(int number)
        {
            Console.WriteLine("veryExpensiveMethod called");
            return true;
        }
 
	public static void Main()
	{
	 var numbers = new []{1,2,3,4,5};
	 IEnumerable<int> nums = numbers.Where(i=> veryExpensiveMethod(i));
	 // deferred
	 int count = nums.Count();
	 Console.WriteLine("Numbers: {0}", count);
	 // following will execute veryExpensiveMethod again 5 times(because 5 elements are in the "filtered" sequence)
	 nums = nums.ToList();
	 // not deferred, using the Count property of List<T>
	 count = nums.Count();
	 Console.WriteLine("Numbers: {0}", count);
	 // following Count() will not call 'veryExpensiveMethod' implicitely because nums is now a List<T>
	 count = nums.Count();
	 count = nums.Count();
	 count = nums.Count();
	}
}

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