One of our users is facing the migration of a large VB6 application and found that the coders often declared local variables using this "concise" syntax:

    Dim x1, x2, y1, y2 As Integer

It is evident that the original intention was to declare four Integer variables. The truth is, this statement declares only y2 as an integer variable, whereas the type of x1, x2, and y1 variables is affected by Defxxx statements (e.g. DefInt or DefDbl). If the current file contains no Defxxx statement, then the type of these variable is Variant. This was a common misconception among less experienced VB6 developers or developers that grew up with C or C++.

Both the Upgrade Wizard and VB Migration Partner convert the first three Variant variables into VB.NET "As Object" variables, which is formally correct but isn't what the original developer meant. Our user asked whether there was anything he could do about it. Quite surprisingly, VB Migration Partner offers a neat and elengant solution to this issue.

In fact, if you are migrating a VB6 application written by developers who consistently applied this sloppy coding practice, you can help VB Migration Partner to restore the intended data type by means of one or more PreProcess pragmas. More precisely, you need one pragma to account for Dim statements with two variables, another pragma to account for Dim statements with three variables, and so forth:

'## PreProcess "\b(?<kw>Private|Public|Dim|Static)\b\s+(?<v1>\w+)\s*,
"${kw} ${v1} As ${type}, ${v2} As ${type}", true

'## PreProcess "\b(?<kw>Private|Public|Dim|Static)\b\s+(?<v1>\w+)\s*,
"${kw} ${v1} As ${type}, ${v2} As ${type}, ${v3} As ${type}", true

'## PreProcess "\b(?<kw>Private|Public|Dim|Static)\b\s+(?<v1>\w+)\s*,
"${kw} ${v1} As ${type}, ${v2} As ${type}, ${v3} As ${type}, ${v4} As ${type}", true

'## PreProcess "\b(?<kw>Private|Public|Dim|Static)\b\s+(?<v1>\w+)\s*,
"${kw} ${v1} As ${type}, ${v2} As ${type}, ${v3} As ${type},
 ${v4} As ${type}, ${v5} As ${type}", true

Notice that these pragmas account for variables and class fields declared with Dim, Static, Public, and Private keywords. You can easily create similar PreProcess to account for more than five variables in a single line.

When these pragmas are used, the above Dim statement is expanded into the following VB6 code immediately before the migration begins:
    Dim x1 As Integer, x2 As Integer, y1 As Integer, y2 As Integer
which, of course, is translated to VB.NET as:
    Dim x1 As Short, x2 As Short, y1 As Short, y2 As Short

Important Note: Keep in mind that these pragmas affect may mistakenly affect the type of variables that SHOULD remain Object variables. Always double check that the resulting VB.NET code works as intended.

Problem solved! 

Update (October 3, 2008): Marco Giampetruzzi (from the VB Migration Partner Team) found a simpler and better way to solve the same problem, as you can read here.