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Postings from April 2004
On Wed, Apr 14, 2004 at 10:00:25PM +0100 hv@crypt.org wrote:
> Tassilo von Parseval <tassilo.parseval@post.rwth-aachen.de> wrote:
> :That's what dualvars usually do. A variable has such a split personality
> :whenever
> :
> : $var+0 ne $var;
>
> It isn't quite as simple as that: I wouldn't call "00" a dualvar, even
> though it satisfies the above inequality.
You are right. It's trickier than that.
> Perhaps C< $var + 0 != "$var" + 0 > would be an adequate test?
That suffers from the same problem:
ethan@ethan:~$ perl -MScalar::Util=dualvar
$a = dualvar(0, "string");
print $a + 0 == "$a" + 0;
__END__
1
The problem seems to be that a string often enough evaluates to 0 when
used in numerical context.
> The canonical example of dualvars is of course $!.
>
> For Math::BigInt, if it is worth checking for such things at all, it
> would probably make most sense to prefer the numeric value. However,
> care needs to be taken not to end up getting perl's default coercion
> for some number to big for it to represent - that would rather defeat
> the point. However, default coercions never create a dualvar, so as
> long as there is a reliable (and efficient) way to check for them,
> no ambiguity should arise.
Which leads to the question what a reliable pure-Perl way of discovering
the dualvarness of a variable is. One probably needs to branch into XS
to do that and so there maybe should be a Scalar::Util::isdualvar()?
Tassilo
--
$_=q#",}])!JAPH!qq(tsuJ[{@"tnirp}3..0}_$;//::niam/s~=)]3[))_$-3(rellac(=_$({
pam{rekcahbus})(rekcah{lrePbus})(lreP{rehtonabus})!JAPH!qq(rehtona{tsuJbus#;
$_=reverse,s+(?<=sub).+q#q!'"qq.\t$&."'!#+sexisexiixesixeseg;y~\n~~dddd;eval
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