Am Montag, 2. Mai 2005 21.27 schrieb Matthew Sacks:
Hi Matthew,
it seems indeed strange...
> I am reading somebody else's code, always a good learning process. The code
> is about a telephone contact list. The intent of this line of code is
> clear: 'does the logged in person have a cell phone, and does the cell
> phone have the attribute line=dc'
>
> There is one confusing step in the syntax:
>
> if ((@{$info{$loggedin}}{cell}) and
> (@{$info{$loggedin}}{line} eq 'dc'))
> {stuff to
> execute}
We have two similar data structures, one of it is
@{$info{$loggedin}}{line} eq 'dc'
> When I read the condition, this is what I se
> a) $loggedin is scalar
> b) $loggedin is used as a hash key
> c) info is a hash
> d) since we retrieve on thing from the hash, there is a '$' in front of
> info
> e) $info{$loggedin} is enclosed inside @{}
> f) @{} is a way of derefencing an array reference.
> g) $info{$loggedin} is inside @{}, so we have @{$info{$loggedin}}
> h) does @{$info{$loggedin}} evaluate to an array? That would confuse me
> because {cell} imposes {} on an array?
> i) does @{$info{$loggedin}}{cell} retrieve something from a hash? Also a
> confusion, because of the @
This point confused me too, so I did:
use strict; use warnings;
use Data::Dumper;
my %hash=(a=>'b');
my %info;
my $loggedin=99; # :-)
@{$info{$loggedin}}{line}='ec';
@{$info{$loggedin}}{cell}=1;
print Dumper %hash;
print Dumper %info;
# this prints:
$VAR1 = 'a';
$VAR2 = 'b';
$VAR1 = '99';
$VAR2 = {
'cell' => 1,
'line' => 'ec'
};
The conclusion of this: The top level data structure is a hash with one
key/value pair.
But I can't see/explain _how_ the key is exactly coming from $loggedin...
The gurus on the list will have the obvious answer.
> j) Where am I going wrong????
My feeling is that the coder was somehow wrong, maybe he did not want this
data structure, it's just the result of a typo. But it seems that it is
functional because the right values are tested in the condition.
I think the coder wanted a simple
$info{$loggedin}->{line} = 'dc'
(build a hash of hashes, but also with just one pair at the top level)
Also and still confused, joe
P.S. Just read Paul Kraus's Confusion - we're not alone :-)
[...]
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