Does this linq query run on every iteration of the for-each loop?

Question

In another question on SO I answered with code like the one below and got a comment that the LINQ-query probably was evaluated in every iteration of the for/each. Is that true?

I know that LINQ-querys does not executes before its items is evaluated so it seems possible that this way to iterate the result can make it run on every iteration?

Dim d = New Dictionary(Of String, String)()    
d.Add("Teststring", "Hello")    
d.Add("1TestString1", "World")    
d.Add("2TestString2", "Test")    

For Each i As String In From e In d Where e.Value.StartsWith("W") Select e.Key
    MsgBox("This key has a matching value:" & i)    
Next

Answer 1

NO... in a foreach, the "GetEnumerator" is called only once (ever), and that is used going forward.

EDIT: I put a statement here about the result set being stored temporarily... that's only true for some cases... not this one, so I took it out.

EDIT: Please forgive this for being overly verbose... but I wanted to show you what is happening... so here's a Console app :)

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            foreach (string item in MyCustomEnumerator()
                .Where(item => item.StartsWith("abc")))
            {
            Console.WriteLine(item);
            }
        }

        static IEnumerable<string> MyCustomEnumerator()
        {
            Console.WriteLine(DateTime.Now);

            yield return "abc1";

            Console.WriteLine(DateTime.Now);

            yield return "abc2";

            Console.WriteLine(DateTime.Now);

            yield return "abc3";

            Console.WriteLine(DateTime.Now);

            yield return "xxx";
        }
    }
}

EDIT: This will result in a DateTime, then abc1, then a DateTime, then abc2, then a DateTime, then abc3, then a DateTime.