Thomas Sandla� skribis 2005-05-04 17:30 (+0200):
> > my ($x, $y); $x = \$y; $y = \$x; $x[0] = 1;
> Hmm, after the my both $x and $y store an undef.
> Then $x stores a ref to undef. Then $y stores
> a ref to ref of undef. I see no circle.
No, again, please do not make the mistake of thinking VALUES have
identity. VARIABLES (containers) do. A reference points to a container,
never to a value directly. The undef in question is the undef value, not
the undef variable (which exists too).
This is something that doesn't change from Perl 5 to Perl 6.
Try in perl (5) the following code:
my ($x, $y);
my ($xx, $yy) = \($x, $y);
They're both undef, but their references are different.
There are names, containers and values.
Declaration and := bind names to containers.
Assignment copies values.
Containers aren't copied.
A reference points to a container.
A name points to a container.
A reference is a value.
The reference isn't to $y's container's value, but to the container.
Regardless of its value. It is also not to the name $y.
> So I think even $x = \$x should just do the right thing.
"The right thing" is the most vague way to describe semantics.
> And that is not in any way different from $x = $x + 5.
> The RHS is evaluated and the resulting value is stored
> in $x.
"$x = $x + 5" overwrites the value of $x's container with the old value
plus five. \$x is the same before and after. The value isn't stored in
$x, but in its container, to which $x is merely a name (implicit
reference).
Juerd
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