In yesterday’s post we saw that the use of the wrong comparison operator with Nothing in an If block can lead to surprising results.  Let’s look at a slightly different case today:

        Dim x As Integer = Nothing

        If x = Nothing Then

            MsgBox(“A true statement – we land here”)

        Else

            MsgBox(“The statement is a lie – we land here”)

        End If

What gets printed?  If the code is intended to print “A true statement…”, is there actually a bug in this code?

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Answer:  The code is correct according to its “specification” (I’m using the term loosely here J), so from a technical point of view there is no bug here.   However, from a code readability and maintenance point of view, I’d argue that there is a bug.

The Nothing literal in VB means “default value for this type”, and for an Integer that would be 0.  So the code above is exactly equivalent to this:

    Dim x As Integer = 0

    If x = 0 Then

        MsgBox(“A true statement – we land here”)

    Else

         MsgBox(“The statement is a lie – we land here”)

    End If

Now that’s way more readable than the version above, and dramatically reduces the potential for confusion.  In general*, if you ever find yourself writing “= Nothing” in a conditional expression, you should either be changing the = to “Is” (as we saw yesterday), or you should change Nothing to the actual default value if possible.