[ apologies for the duplicate email message from my last post--mail
client problems... ]

On Jan 6, 2004, at 11:50 AM, Simon Cozens wrote:

But here what I'm copying is the _contents_ of the hash slot--so I'm
copying a PerlString PMC, for instance.

And here I'm not making a copy, but also the thing I'm taking a
reference to is not the same thing I copied above. Here, it's a
reference to a hash slot.

So maybe the way to think about it is:

$a = $hash{bar};
#This finds the hash slot, pulls out its contents, and copies that
contents into $a.

$b = \$hash{bar};
#This finds the hash slot, takes a reference to it, and places that
reference in $b.

So the first case involves copying a string, and the second involves
creating a reference to a hash slot. In particular, if the hash is
initially empty, the first case should end up with undef in $a (so
nothing actually copied, if undef is a singleton), but $b would
(presumably) still contain a real reference (to a hash slot which
doesn't contain anything yet), which would create a hash entry if you
"$$b = 'goo'". And that reference-to-a-hash-slot is probably a separate
special PMC (it needs to keep track of the hash and key, and work even
if the hash is empty).

JEff