On 29 Jan 2003 14:29:52 -0500, Aaron Sherman wrote (in part):
ajs> As for the argument that testing for true non-existentness is a
ajs> burden, check out the way Perl5 does this. Hint: there's a central
ajs> sv_undef, and that's not what array buckets are initialized to....
Either you're dead wrong, or you typo'd there. After
my @a;
$a[4] = 1;
The array buckets @a[0..3] most certainly ARE initialized to &PL_sv_undef
in p5. That's how C<exists $a[2]> knows to return false (&PL_sv_no)
instead of true (&PL_sv_yes). And, yes, C<delete $a[4]> re-sets that slot
to point to the one true central undef again. This is different from what
happens on C<undef $a[1];> -- that actually makes a new SV which is a
*copy* of the central undef and makes that the new value in that slot.
Thus, even with just the above sequence, C<exists $a[1]> would now be true
in p5.
Please, folks, this discussion's getting complicated enough without making
mistaken claims about what p5 currently does, even when that's by accident.
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