So after many hours of downloading I’ve acquired the March CTP for Orcas and have
it running both at home and at work under Virtual PC 2007. I decided to jump
into LINQ as I’m entirely jazzed about this but one of my first few experiments with
it, while a little unorthodox, has me scratching my head a bit.
Consider if you will the following code, which retrieves a list of all files in the
root folder of the C drive and then, using LINQ, selects a set of them at random using
the FlipACoin method. Then I iterate through the list, outputing the contents
of the results of my query … or so I thought.
1:
using System;
2:
using System.Linq;
3:
using System.Collections.Generic;
4:
using System.Text;
5:
6:
namespace TestConsole07
7: {
8:
class Program
9: {
10:
static Random rnd = new Random();
11:
12:
static
void Main(string[]
args)
13: {
14: var myList =
15: from f in System.IO.Directory.GetFiles(@"C:\")
16: where FlipACoin()
17: select System.IO.Path.GetFileName(f);
18:
19: Console.WriteLine();
20: Console.WriteLine("First Loop");
21: Console.WriteLine("-----------");
22: foreach (string loopFile in myList)
23: {
24: Console.WriteLine(loopFile);
25: }
26:
27: Console.WriteLine();
28: Console.WriteLine("Second Loop");
29: Console.WriteLine("-----------");
30: foreach (string loopFile in myList)
31: {
32: Console.WriteLine(loopFile);
33: }
34:
35: Console.WriteLine();
36: Console.WriteLine("Press Enter To Exit");
37: Console.ReadLine();
38: }
39:
40:
static
bool FlipACoin()
41: {
42:
return rnd.Next() >
(int.MaxValue / 2);
43: }
44: }
45: }
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When this code is executed, what happens is very odd. Here is the output from
a sample run:
First Loop
———-
AUTOEXEC.BAT
eula.1033.txt
install.ini
install.res.1033.dll
MSDOS.SYS
NTDETECT.COM
ntldr
pagefile.sys
sde.bmp
SDE_VSD.MSI
unicows.dll
Second Loop
———–
boot.ini
CONFIG.SYS
install.exe
install.ini
install.res.1033.dll
NTDETECT.COM
SDE_VSD.MSI
unicows.dll
Press Enter To Exit
Notice that despite the fact that I’m iterating over the same list each time, the
files listed as different. This means that each time I begin to iterate over
the list the LINQ “query” is being executed again, and a new set of values are being
returned from FlipACoin.
I can undoubtedly say this wasn’t what I expected, but what I can’t seem to determine
is if this is a feature of LINQ or if this is a bug. My first response would
be bug, but that is because whenever I believe I’ve expressed my intent clearly and
don’t get the response I expect, I call that a bug.
What do you think? Is this just a cool feature that won’t come up very often?
Or is this a dent in the armor of LINQ?