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Today I investigated a logical bug in our software and figured out that this is related to the way VB.NET thread variables inside a loop. Let's say I have the following code: Dim numbers As New List(Of Integer) From {1, 2, 3, 4, 5} For Each number As Integer In numbers Dim isEven As Boolean If number Mod 2 = 0 Then isEven = True End If If isEven Then Console.WriteLine(number.ToString() & " is Even") Else Console.WriteLine(number.ToString() & " is Odd") End If Next produces the following output 1 is Odd 2 is Even 3 is Even 4 is Even 5 is Even The problem is that isEven is declared but not assigned. In this specific case, it would be correct to write dim isEven as Boolean = false but I haven't done this. In VB.NET, a variable that is declared inside a for loop keeps its value for the next itaration. This is by design: http://social.msdn.microsoft.com/Forums/en/vblanguage/thread/c9cb4c22-d40b-49ff-b535-19d47e4db38d but this is also dangerous pitfall for programmers. However, until now, I haven't been aware of this problem/behaviour. Until now. Most of our code base is C# anyway, which doesn't allow the use of an uninitialized variable, so there is no problem. But we have some legacy code that is written in VB.NET that we have to support. I don't think that anyone of our dev team has ever used this with purpose. If I explicitly want to share a variable over iterations inside a for loop, I declare it outside the scope. So the best thing would be to generate a warning or even an error in this specific case. But even with Option Explicit / Option Strict this does not generate a warning / an error. Is there

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