[tpm] dereferencing anonymous hashes

[Rob Janes]

you're a php guy, right?

$x = (); is a list assignment to a scalar.  scalar conversion results in the
scalar ($x that is) being assigned the count of the number of items in the
list.  0 or zero.

$x = {}; assigns a reference to an anonymous hash.

On 4/10/07, Fulko Hew <fulko.hew at gmail.com> wrote:
>
> On 4/10/07, Fulko Hew <fulko.hew at gmail.com> wrote:
> > I always seem to have a problem dereferencing anonymous hashes...
> > (a mental block, or I'm just mental!)
> >
> > In a subroutine I create the thing as such:
> >
> > sub foo {
> >   my $device = {};                           # create an anonymous hash
> >   $config{$cfg}{device} = \$device;    # And stick it into the major
> data structure
> >
> > $device{$devId}{status) = 'ok';         # and populate the anonymous
> hash
> > $device{$devId}{msgCnt}++;
> > }
> >
> > Then later on I want to extract the status:
> >
> > my %device = ${$config{$cfg}{device}};
> > $status = $device{$devId}{status};
> >
> > but this isn't quite right.  ;-(
>
> Answering my own question...
> I was close, but not cigar.  What I should have been using was:
>
> my $device = ();
> ...
> my %device = %{$config{$cfg}{device}};
>
> because the reference I was trying to retrieve was a reference to a hash,
> not a reference to a scalar as in my first 'n' tries.
>
> I'm sure I had the dereference correct a number of times, but without
> the anonymous hash creation correct at the same time, It didn't
> work.... Nope, I just tried it as: my $device = {}; and that still
> worked.  It makes me wonder then... whats the subtle difference
> between
> $x = () and $x = {} when dealing with hashes and their references?
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