Nothing big, just a small LINQ query [modified]

[0x3c0]

I've recently been working on a small application which tells me which user groups I'm in. After tossing WMI aside in this case due to slowness, I discovered the System.Security.Principal namespace:

IEnumerable<string> groups = from IdentityReference irc in currentPrinciple.Groups
let value = irc.Translate(typeof(NTAccount)).Value
let index = value.IndexOf('\\')
select value.Substring(index + 1);

modified on Monday, May 18, 2009 3:49 AM

[Robert Rohde]

I've not really worked with .Net 3.5 and Linq but shouldn't the last line be select arr[count - 1]?

[0x3c0]

No, the format of the output is ComputerName\UserGroup. If you're sharing across a network it'd be useful, but it looks messy IMHO Edit: My mistake. I refactored it to add null-checking and made a mistake

modified on Sunday, May 17, 2009 11:55 AM

[PIEBALDconsult]

Yeah, that seems right, just tried it myself, needs -1.

[0x3c0]

After a quick check, that's right. I've just updated the snippet

[PIEBALDconsult]

I don't see why you feel a need to check for null here; have you experienced any nulls? Plus the Split is needless (and costly). I wrote it as:

public static System.Collections.Generic.IEnumerable
GetGroups1
(
System.Security.Principal.WindowsIdentity Identity
)
{
foreach
(
System.Security.Principal.IdentityReference grp
in
Identity.Groups
)
{
string temp = grp.Translate ( typeof(System.Security.Principal.NTAccount) ).Value ;
int offs = temp.IndexOf ( '\\' ) ;

    yield return ( offs == -1 ? temp : temp.Substring ( offs + 1 ) ) ;
}

yield break ;

}

Which appears to be about 3% quicker than yours. Here's yours without the Split:

public static System.Collections.Generic.IEnumerable
GetGroups3
(
System.Security.Principal.WindowsIdentity Identity
)
{
return
(
(from System.Security.Principal.IdentityReference irc in Identity.Groups
let value = irc.Translate(typeof(System.Security.Principal.NTAccount)).Value
let offs = value.IndexOf ( '\\' )
select offs == -1 ? value : value.Substring ( offs + 1 ) )
) ;
}

It's about 2.6% quicker than yours.

[0x3c0]

I really hadn't thought about it like that. Thanks for the tips, and I've changed the snippets accordingly. FWIW, there may not be any need to use offs == -1 ? value : value.Substring ( offs + 1 ) ). If offset is -1, then value.Substring(0) will just return value, so there's no need for the conditional (unless you're counting string sizes in memory) As for the nulls, I did indeed experience some, but couldn't reproduce them. Having looked in Reflector, I can't find anything like that; I may have just imagined them

[PIEBALDconsult]

:doh: Of course! That eliminates the offs variable. yield return ( temp.Substring ( temp.IndexOf ( '\\' ) + 1 ) ) ;

[0x3c0]

Probably my coding style, but I would personally prefer to keep the offs variable. If I ever step through a piece of code, I want to be able to have every input where I can see it

[PIEBALDconsult]

I'll occasionally have to add such things to debug, but then I remove them again.