Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

Anonymous — Fri, 08 Jan 2010 09:58:19 GMT

I have to be anonymous here in case it's a breach of NDA, but "= Nothing" came up in a recent MCP exam as part of the code sample. I also think it was a bug, but I'm not sure as obviously I wasn't allowed to take a copy out of the room with me. I believe it's a case of mistranslation from C#.

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

yelinna — Tue, 24 Nov 2009 14:49:54 GMT

I prefer not to use "nulls" or "Nothings" for numeric variables (I prefer 0 or -1 for detecting errors or invalid values). You're right, "Nothing" is confusing.

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

MatthiasBroschk — Sat, 21 Nov 2009 02:42:09 GMT

I really doubt that I will ever use something like this, but it can't hurt to know how it works.

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

Anthony D. Green — Mon, 09 Nov 2009 22:41:31 GMT

Steve,

I'm not sure I follow. The example is meant to show that for comparison puposes over non-nullable Integers Nothing and 0 are equivalent. Could you explain how you are noticing this difference in your code? Please be detailed.

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

Steve — Sun, 08 Nov 2009 19:18:11 GMT

Anthony, you miss understod what I was trying to say.

AS the example shows if you do dim x as int = nothing then x=0 if you don't intialize the variable dim x as int then X<>0 it does equal nothing.

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

Jonathan Aneja — Sun, 08 Nov 2009 01:14:21 GMT

Re: "The fact that nothing can be legally assigned to a value type is a serious problem"

and

"To avoid confusion, value types should not even be able to be used with the nothing keyword."

The logical implication of both those statements is that "it should be illegal to initialize a value type to its default value", which I'm sure we'd all agree is not a good idea :)

Consider the following code in C#:

int x = default(int);

IntPtr y = default(IntPtr);

Process p = default(Process);

The following VB is *exactly* equivalent to those lines:

Dim x as Integer = Nothing

Dim y As IntPtr = Nothing

Dim p As Process = Nothing

Nothing just means "default value for type", not necessarily null.

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

Anthony D. Green — Sat, 07 Nov 2009 01:33:10 GMT

Jason, Novlok;

I don't know if such a restriction is necessary.

Whether equating Nothing with defaultness is logically valid I might argue is contextual.

From a language (English) perspective would we not say that a free item costs Nothing (it doesn't cost anything) or would you say it cost $0.00?

In the case of strings "" and Nothing compare as equal to the VB comparison operator and Len("") = Len(Nothing), And Len(Nothing) = Len(<empty array>).

Furthermore System.Char is a value type (structure) and its default value is ChrW(0) - commonly called the null character. The only way to represent this as a literal in Visual Basic (other than the above function) is to assign it Nothing. In this context assigning Nothing to a value type sets it to the "null" character so it makes sense, no?

Conceptually a glass doesn't contain 0 liters of water - it's empty - there's Nothing in the glass.

So from another angle Emptiness, Nullness, and Nothingness are sufficiently synonymous that I wouldn't say the usage is inherently unsensible or "not good" though I would generally avoid this usage when a more meaningful default value (or literal, such as 0) can be used instead.

-------------

Steve,

What's strange about a variable taking on its default value unless otherwise assigned? That's the entire meaning of a *default* value. What's strange is that other languages make you initialize redundantly, no?

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

Steve — Sat, 07 Nov 2009 01:22:24 GMT

I always thought it strange that VB.net does not acctually initialize value types until they are assigned. For example in the above example if you do not assign the int to nothing then it does treat the int as nothing.

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

Nivlok — Fri, 06 Nov 2009 21:09:26 GMT

I agree with jason. Having a value type evalute to nothing is not good. It is not a dynamic variable that just gets created on the heap. I gets created on the stack and will always evaluate to something even if that something for and int is the number 0. To avoid confusion, value types should not even be able to be used with the nothing keyword.

re: Spot the Bug! – Much ado about Nothing… Part 2! (Jonathan Aneja)

Jason Lind — Fri, 06 Nov 2009 19:45:14 GMT

The fact that nothing can be legally assigned to a value type is a serious problem.