Glenn Linderman <[EMAIL PROTECTED]> writes:
> Russ Allbery wrote:
>> I agree with Tom; I think it's pretty self-evident that they're the
>> same thing. undef means exactly the same thing as null; that's not the
>> problem. The problem is that Perl doesn't implement the tri-state
>> logic semantics that most users of null are used to, which is a
>> different issue.
> So, to paraphrase your statement a bit:
> It is self-evident that they're the same, the problem is that they work
> differently.
No, that's not a paraphrase. That's saying something completely different
which is wrong.
If undef functioned differently than null, that would be a bug. What's
missing is a way to say "I want tri-state logic" as a pragma. When that
pragma is enabled, undef would be the null-like state.
Perl already has exactly the data value that you're looking for. This RFC
is proposing to fix the wrong problem; the things that need to be changed
(conditionally) are the logical operators, not the data value.
> Nota Bene: IEEE floating point defines two different concepts that are
> not numbers, but can be mixed with numbers in expressions: Inf and NaN.
> And actually, there are positive and negative varieties of both Inf and
> NaN. So I guess you might say that they are the same; but the problem
> is that they work differently.
There are positive and negative infinities, but that's a different
situation entirely; infinity is a degenerate value, not an undefined
value. This is the first time I've ever heard of -NaN; are you sure about
that? (There are, in fact, different types of NaN, such as signalling vs.
non-signalling, but that's due to floating point traps and exceptions,
issues that don't crop up in the situations where you want undef/null.)
--
Russ Allbery ([EMAIL PROTECTED]) <http://www.eyrie.org/~eagle/>
