Most query operators is executed not when constructed, but when enumerated.
Consider the following query:
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
class Program
{
static void Main()
{
var numbers = new List();
numbers.Add(1);
IEnumerable query = numbers.Select(n => n * 10);
numbers.Add(2);
foreach (int n in query)
Console.Write(n + "|"); // 10|20|
}
}
The output:
10|20|