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

Comments

# Hugo said on November 6, 2009 12:46 AM:

I didn't know “Nothing means: default value for this type”. Probably because in C# Nothing is null and in SQL "= null" always evaluates to null, I thought we would end in the else part.

Learnt something here, thanks!

# Jason Lind said on November 6, 2009 11:45 AM:

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

# Nivlok said on November 6, 2009 1:09 PM:

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.

# Steve said on November 6, 2009 5:22 PM:

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.

# Anthony D. Green said on November 6, 2009 5:33 PM:

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?

# Jonathan Aneja said on November 7, 2009 5:14 PM:

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.

# Steve said on November 8, 2009 11:18 AM:

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.

# Anthony D. Green said on November 9, 2009 2:41 PM:

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.

# MatthiasBroschk said on November 20, 2009 6:42 PM:

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

# yelinna said on November 24, 2009 6:49 AM:

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.

# Anonymous said on January 8, 2010 1:58 AM:

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#.

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