Question about Lamda Expression

[teguh123]

Sub Test()
    Dim y As Integer = 10
    Dim Lambda As Func(Of Integer, Integer) = Function(ByVal x) x + y
    y = 20
    Console.WriteLine(Lambda(5))
End Sub

So the method vb.net use to generate lamda expression is similar to C++ functor.

So far so good.

What value is displayed when you execute this function? If you said 25, you were spot on. Why 25? Well, the compiler captures and rewrites all of the free variables y to the closure's copy, like so:

Sub Test()
    Dim Closure As New $CLOSURE_Compiler_Generated_Name$
    Closure.y = 10
    Dim Lambda = AddressOf Closure.Lambda_1
    Closure.y = 20
    Console.WriteLine(Lambda(5))
End Function

I still do not understand why Microsoft decide to change the second y=20 into closure.y=20?

The first closure.y=10 make sense. In fact, if I were microsoft, a more normal way to generate the code will be to have a variable would be to do

Sub Test()
    Dim Closure As New $CLOSURE_Compiler_Generated_Name$
    y=10
    Closure.y = y
    Dim Lambda = AddressOf Closure.Lambda_1
    'Closure.y = 20 Remove this line.
    Console.WriteLine(Lambda(5))
End Function

Why Microsoft do it the microsoft way instead of the way that make more sense? The microsoft way is when y change value then the Lambda variable also change. It becomes a different function. Also what are the rules where microsoft will change y=10 into Closure.y=10?

Sub Test()
    For I = 1 To 5
        StartThread(Function() I + 10)
    Next
End Function

Won't work properly because I keeps changing. What I think would happen is that thread may actually be started sometimes latter, say during doevents or latter.

At that time I would have became 5 or 6 and all threads will simply print 15. Wouldn't happen if Microsoft do things the normal my way.

http://msdn.microsoft.com/en-us/magazine/cc163362.aspx

Sub Test()
    For I = 1 To 5
        Dim x = I
        StartThread(Function() x + 10)
    Next
End Function

How the hell doing Dim x=i change anything?

Microsoft compiler change all occurrence of I=1,2,3,4,5 into Closure.I=1,2,3,4,5

Why microsoft don't do the same for x?