[Resolved] C# to VB Adaption Problem with Lambda Expressions

[Sonhospa]

Hey Luc, thanks for the hint, I'm just about downloading SP1. Still I'm afraid it wouldn't solve the problem I have: As I wrote I put all the extensions into a DLL which I'm referencing from my main VB code as well as from VB and C# test procedures. It seems pretty clear that there must be something wrong with the Lambda expressions. Would you have a look at them, please?

[Luc Pattyn]

I seldom use lambda's, I probably can't help you. If they are in a separate DLL, why aren't you using C# for them? :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

[Sonhospa]

You misunderstood me. All the extension methods, which contain the C# 'yield' operator, are in a separate DLL. My application is in VB so I have to call the extensions from VB using adapted code... and the sample code (pls. see link in the initial message) is in C# where the Lambdas work.

[Lost User]

Cool - I never missed the statement in VB, until this question popped up :)

Bastard Programmer from Hell :suss:

[Simon_Whale]

VB2010 has introduced sub(parameter) into the lambda specification. I haven't tested it but wouldn't the following work?

items.WithProgressReporting(sub(progress) worker.ReportProgress(progress) end sub).forEach(function(item) thread.Sleep(10)))

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[User 7825588]

Try changing this line:

items.WithProgressReporting(Function(progress)
worker.ReportProgress(progress)).ForEach(Function(item) Thread.Sleep(10)) ' simulate some real work

To this:

items.WithProgressReporting(Function(progress) _
worker.ReportProgress(progress)).ToList.ForEach(Function(item) Thread.Sleep(10)) ' simulate some real work

The .ForEach extension method doesn't work with IEnumerables and since that's what WithProgressReporting returns, the resultset must first be cast as a Generic List. Also, I don't know for sure, but it looks like the converter inserted an extra line break. That's why I added the underscore to the end of the first line.

[Estys]

I always have trouble with anonymous delegates in VB so I factored them out :

Class Program
Shared worker As BackgroundWorker
Public Shared Sub Main() 'ByVal args As String())
worker = New BackgroundWorker()
worker.WorkerReportsProgress = True
AddHandler worker.DoWork, AddressOf DoWork
AddHandler worker.ProgressChanged, AddressOf ProgressChanged
worker.RunWorkerAsync()
Console.Read()
End Sub

Private Shared Sub DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
    Dim items = Enumerable.Range(1, 1000)
    items.WithProgressReporting(AddressOf ReportProgress).ForEach(AddressOf DoSleep)
End Sub
Private Shared Sub ReportProgress(ByVal progress As Integer)
    worker.ReportProgress(progress)
End Sub
Private Shared Sub DoSleep(ByVal item As Integer)
    Thread.Sleep(10)
End Sub
Private Shared Sub ProgressChanged(ByVal sender As Object, ByVal e As ProgressChangedEventArgs)
    Console.SetCursorPosition(1, 0)
    Console.Write(e.ProgressPercentage)
End Sub

End Class

Cheers

[Terence Wallace]

Hey just wanted to say thanks Luc that link got me to several other links on the subject and could prove quite useful to me in the very near future. Thanks again. This is now supported in VS 2010 SP1, with the Async CTP, see: http://msdn.microsoft.com/en-us/vstudio/gg497937[^] Also see: http://www.microsoft.com/downloads/en/details.aspx?FamilyID=4738205d-5682-47bf-b62e-641f6441735b&displaylang=en[^]

"If you think it's expensive to hire a professional to do the job, wait until you hire an amateur." - Red Adair

[DavidSherwood]

In VB, a function that returns void is a "Sub". This is true with lambda function as well. So your ForEach lambda should be

ForEach(Sub(item) Thread.Sleep(10))

[Simon_Whale]

Only true with 2010 though, as there is many time I would loved to of used it in my current project that is 3.5 framework

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[Sonhospa]

Hi Simon, sorry for the late response which was due to a short holiday of mine. Thanks for your hint which pushed me in the right direction: In the end, all I had to do was change "function" into "sub" in VB. It's finally solved now, and the line

items.WithProgressReporting(Sub(progress) worker.ReportProgress(progress)).ForEach(Sub(item) Thread.Sleep(10))

works, as well as Estys suggestion to factor out the subs. No "end" needed here. Regards - Mick

[Simon_Whale]

Glad it helped :thumbsup:

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[Sonhospa]

Hi Member... ;) , sorry for the late response which was due to a short holiday of mine. Thanks for your hint which unfortunately didn't work: In the end, all I had to do was change "function" into "sub" in VB. It's finally solved now, and the line

items.WithProgressReporting(Sub(progress) worker.ReportProgress(progress)).ForEach(Sub(item) Thread.Sleep(10))

works, as well as Estys suggestion to factor out the subs (no "end" or "ToList" constructions needed). Regards - Mick

[Sonhospa]

Hi Estys, sorry for the late response which was due to a short holiday of mine. Thanks for your hint which, together with the other guys' ideas, pushed me in the right direction: In the end, all I had to do was change "function" into "sub" in VB. It's finally solved now, and the line

items.WithProgressReporting(Sub(progress) worker.ReportProgress(progress)).ForEach(Sub(item) Thread.Sleep(10))

works, as well as your suggestion to factor out the subs. Just to complete: In your snippet I had to change the definition of 'items' to:

Dim items As IEnumerable(Of Integer) = Enumerable.Range(1, 1000)

in VB. But the most important thing: It works - and I hope I understand it a little better ;) Thanks again, regards - Mick

[Sonhospa]

Hi David, sorry for the late response which was due to a short holiday of mine. Thanks for your hint which pushed me in the right direction: In the end, all I had to do was simply change "function" into "sub" in VB. It's finally solved now, and the line

items.WithProgressReporting(Sub(progress) worker.ReportProgress(progress)).ForEach(Sub(item) Thread.Sleep(10))

works, as well as Estys suggestion to factor out the subs (slightly changed). Thanks again, regards - Mick

[Estys]

Michael Schäuble wrote:

I had to change the definition of 'items'

That's odd, with me it worked as I posted it. I'm on .NET 3.5, VB Express 2008 Cheers

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