Friday, July 25, 2008

MyClass in VB.Net

It's always a bit of a shock when you find something you've missed in a language you've used for years. I'm mostly a C# person, but I thought I knew pretty much all of VB.Net's quirks by now. But I totally missed 'MyClass'.

'MyClass' allows a class to access methods and properties as declared on itself, irrespective of them being overridden further down the inheritance heirachy. It's like using 'Me' if all the 'overridable's were removed.

Since there's no C# equivilent this was a big surprise to me, but it shouldn't have been - it's only doing the same as 'MyBase' does (against a type's ancestor): executing properties / methods by specific type address, not via virtual dispatch. As the IL for this sample shows:

Public Class Class1
Public Overridable ReadOnly Property Name()
Return "Class1"
End Get
End Property
End Class

Public Class Class2
Inherits Class1
Public Overrides ReadOnly Property Name()
Return "Class2"
End Get
End Property

Public Function GetNames() As String
Dim lines(3) As String
lines(0) = MyBase.Name
lines(1) = MyClass.Name
lines(2) = Me.Name
Return String.Join(",", lines)
End Function
End Class

Public Class Class3
Inherits Class2
Public Overrides ReadOnly Property Name()
Return "Class3"
End Get
End Property
End Class
Calling new Class3().GetNames() produces the following (edited for brevity)

     // mybase - explicit dispatch to class1
L_000b: call instance object ConsoleApplication1.Class1::get_Name()

// myclass - explicit dispatch to class2
L_001a: call instance object ConsoleApplication1.Class2::get_Name()

// me - virtual dispatch, will resove to class3's implementation
L_0029: callvirt instance object ConsoleApplication1.Class2::get_Name()
So the output eventually is 'Class1, Class2, Class3'. Nifty. That being said, I can't honestly say I've ever really needed this, so it might go back into the 'curios' collection. Useful in a pinch maybe, but surely it's a smell? As if designing-for-subclassing wasn't hard enough as it is...

PS: Interestingly the Reflector disassembler doesn't understand this either, so it wasn't just me that missed it: Reflector thinks the VB was:

Public Function GetNames() As String
Dim lines As String() = New String(4 - 1) {}
lines(0) = Conversions.ToString(MyBase.Name)
lines(1) = Conversions.ToString(Me.Name) ' got this wrong
lines(2) = Conversions.ToString(Me.Name)
Return String.Join(",", lines)
End Function

Thursday, July 17, 2008

Using Extension Methods in .Net 2.0 from VB.Net

So despite what ScottGu originally said, Extension Methods don't 'just work' for VS 2008 projects targeting .Net 2.0.

There's no end of blog posts describing the workaround - add your own ExtensionAttribute class to get it working - but all the samples are in C# (which is interesting in of itself). So here's the VB.Net version:

Namespace System.Runtime.CompilerServices
<AttributeUsage(AttributeTargets.Method Or AttributeTargets.Assembly Or AttributeTargets.Class)> _
Public Class ExtensionAttribute
Inherits Attribute
End Class
End Namespace

...and why am I bothering to blog about this rather trivial conversion? Because of the key gotcha: make sure you put this in a project with no root namespace set:

That had me banging my head on the table for too long.

As did the next one: extension methods only show up under the 'All' tab in IntelliSense - obviously too advanced for mere Morts. I gotta remember to turn that off: using VB is bad enough without the IDE patronising you as well.

Interestingly, if you get the AttributeUsage declaration wrong on the attribute, you get this error:

"The custom-designed version of System.Runtime.CompilerServices.ExtensionAttribute ... is not valid"

Fascinating. So this hackery works by design, it's just not really supported as such.

More reading: MSDN documentation on Extension Methods in VB

Tuesday, July 15, 2008

Continuous Integration in TFS 2008: Part 1

Many people now accept the benefits of a regular / continuous integration cycle (even if they don't actually practice it themselves). Picking up the pieces after someone's broken the checked-in source code, especially if it's not picked up for a few days, can be a real time waster.

Like many agile practices, however, the cost / benefit is hard to quantitatively analyse. It's far easier to justify therefore if it's really easy to setup: as the costs tend to zero the benefits become essentially 'free'. And you could argue that tools like CruiseControl.Net have made it pretty easy.

Personally, having spent significant sections of the last 3 years getting CCNet / Nant build cycles going on various projects, I'd beg to differ. Sure, it's really easy to setup CCNet / Nant (or CCNet / MSBuild) to build your solution, but that's only the first step in the process. Typically you also want to do things like:
  • Import the latest built version of external dependencies (ie components maintained outside of the solution being built)
  • Execute unit tests
  • Execute integration tests (so config files pointing at databases etc... have to be in the right place)
  • Package the build outputs nicely ('xcopy ready')
  • Deploy and install into test environments
CCNet and NAnt don't really give you this stuff 'out of the box'. You spend time gluing bits together, inventing your own build process and so on, and maintaining this stuff seems to get out of control very easily. Deploy and install is a particular minefield, because somewhere in there you have to start doing configuration file substitution (put your test server settings in the web.config etc...). And doing all this in XML just rubs salt into the wound.

You can handle most of this by hand on small projects, but the last app I worked on had five or six deployable parts to it (webservices, windows services, Winforms with ClickOnce manifests and the like), each of which had 20 or so settings to change for each of 7 different environments and the differing systems it integrated with. That's 100's of settings to keep track off, without even getting into the Biztalk artefacts, and that was only one of several projects of similar complexity. Automation's a no brainer at that point.

My solution to try and scale back the per-project cost of managing this was my own open source project SNAK. This attempted to commoditize a standard build / test / package / deploy process that you could implement on your side by pretty much setting a single variable at the top of a build script. And I think it works reasonably well: but it's clearly not the answer, not least because it took a fair amount of my (and others) time, of which I have very little.

So I was very, very hopeful when I started looking at the CI support in TFS 2008. Microsoft were really bashed over CI (lack of) in 2005, but this time round it looks like they've delivered:

You pretty much pick your solution file:

...your output directory...

...and your build frequency, and off you go:

Given how hard it was to deal with VSTS tests under CI in 2005 (because the test file was always in the wrong place), this screen will be a real pleasure to some:

And if you've tried to implement a build output retention policy in NAnt, you'll really appreciate this:

So up until now, absolutely fantastic. But then I had a few issues, which I'll deal with in Part 2 (so as not to take the gloss off the good bits above).

[I was due to present on this topic at the Perth .Net user group the other week, but a failing laptop saw to that (not the way I was expecting the demo to fail!). Since there's now no slots till Xmas, I've recycled some of the content into this post. The laptop was lobotomized and is recovering well...]

[Readify are doing a Dev Day in Perth on the 29th, with TFS as one of the tracks, so I'd be surprised if they didn't cover this there]

Monday, July 07, 2008

Recycling old posts?

Sorry about that. I re-tagged a few articles over the weekend, and I think Blogger has got confused and bounced them into my feed as if they were new posts. Unfortunately some of them were, so it's all a bit of a mess.

New posts were actually:
* Finally: PowerShell as build language
* Using PowerShell to export the Windows Feeds list

Normal service will resume shortly...

Friday, July 04, 2008

Using PowerShell to export the Windows Feeds list

Moved computers recently, and one of the things I realised I lost was my RSS feeds list. It was probably a blessing (I just tend to accumulate subscriptions otherwise), and maybe I should be using a reading service of some nature, but there you are.

Anyway given I'm all Mesh'd up, I though I'd copy my feeds list into my Mesh folder (like my bookmarks), so I'd have a backup and this wouldn't happen again. Only I couldn't find where the feeds list actually lives. Instead there's a whole API for dealing with it...

...which is surprisingly easy to use, and works like a treat in PowerShell (I'm always amazed at it's ability to 'just work' with things like COM objects). So I just exported the list instead:

# Dump the contents of the Windows Feeds store to an XML file

[xml]$feedsListDocument = "<feeds/>"
$feedsList = $feedsListDocument.get_DocumentElement();
$feedManager = new-object -com "Microsoft.FeedsManager"

$feedManager.RootFolder.Feeds | % {
$feed = $_;
$feedXml = $feed.Xml(-1, 0, 0, 0, 0)
'<feed Name="{0}">{1}</feed>' -f $feed.Name,$feedXml

Easy as. The XML it spits out is overly large (since it includes all the article contents from the cache), but for the MB involved it barely seems worth refining it.

Update 2008-07-17: So like the very next day I realised I could have just sync'd the feed list into Outlook, and asked it to export it as OPML. But syncing into Outlook blew my tiny mailbox quota (these feeds are suprisingly large) so I ended up back doing this again anyway. Then it turned out that IE can export the feed list as OPML too (File \ Import and Export - you'd think I'd have noticed originally) - but I still like having a script because I can schedule it.

Note to self: It is definitely time to find a blog that can cope with XML a bit better

Finally: PowerShell as build language

I've never really got into MSBuild, which surprised some people given how much time in the last four years I've spend mucking about with CCNet / NAnt. It was partly that we did a bit of investigation when MSBuild came out, and saw a couple of things we didn't really like about it and decided to wait for v2 (ie Team Build in TFS 2008). Partly.

More fundamentally however the problem is that MSBuild is just too similar to NAnt, and my considered opinion after years of usage is that NAnt sucks, or to be more specific, XML is a terrible 'language' for writing executable code. Fowler puts it pretty well:
"After all until we tried it I thought XML would be a good syntax for build files"
Sure it's fine for the IDE to write that stuff out (though even then you have to look at it and wince, right), but for humans who want to customise their build process? Jesus wept. Variable scope: gone. Explicit parameters for subroutines (targets): gone. Its fine when it's simple, but once you start looping and branching and using temporary variables it's just a great big mess of angle brackets that even it's mother pities. And debugging? Now there's a story...

There's a time and a place for the angle bracket tax, and this isn't it. Square peg, round hole.

So given how amenable for DSLs PowerShell has proven to be, I've been holding my breath for some kinda PowerShell rake-alike.

And here it is: Introducing PSake

(Also Microsoft themselves are thinking about it, and canvassing for opinions about whether it's a good idea or not.)

Sadly (actually quite the opposite) I'm not actually having to deal with the build process on my current project, so I don't really have much excuse to play with it. But I dream of a future in which the TFS Team Build project wizard kicks out a PS1 file instead. It'd certainly make fixing some of it's shortcomings a whole heap easier (that's a subject for a future post)

Edit [14/7/08]: Most requested feature for MSBuild? Debugging. Obviously this'll be interpreted by the MSBuild team as a need for a debugger, but maybe they should have used a language that already had one.

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