Re: Putting an array into a hash gives an unexpected reference to the hash itself.

in reply to Putting an array into a hash gives an unexpected reference to the hash itself.

... I am still puzzled as to why I got a reference to the hash value 'email' => $services{'service1'}{'email'} rather than a reference to say 'email' => $maintainers[0];

The problem is that Dump() does not 'know' that the reference that is the value of both $services{service1}{email} and $services{service2}{email} derives from the @maintainers array, i.e., \@maintainers (not the $maintainers[0] array element). All Dump() 'knows' is that one reference in the data structure it is analyzing (by recursive traversal of a tree of references!) is the same as another, and it tries to let you know (without quotation marks) this because it's probably significant. (Perl has a great deal of introspective ability, so it might be possible (but probably not – see Update below) to make a function like Dump() smart enough figure out the name of the original referent (if it ever had and still has a name!), but if it is, the author of the module didn't know about the possibility or didn't care to make use of it.)

Update: OTOH, it's easy to imagine situations in which the original name of a variable is gone beyond even the ability of PadWalker to access it. In the example below (don't try this at home: bug: dependence on execution order), the name of the lexical @ra array is, I believe, absolutely gone upon exit from the scope in which it is defined, but the data lives on as long as there is a reference to it.

>perl -wMstrict -le
"use Data::Dumper;
 ;;
 {
 my @ra = qw/ worker@company.com manager@company.com /;
 sub AR { return \@ra; }
 }
 ;;
 my %services = (
   service1 => { email => AR() },
   service2 => { email => AR() },
   );
 ;;
 print Data::Dumper->Dump( [ \%services ], [qw/*services/] );
"
%services = (
              'service1' => {
                              'email' => [
                                           'worker@company.com',
                                           'manager@company.com'
                                         ]
                            },
              'service2' => {
                              'email' => $services{'service1'}{'email'
+}
                            }
            );
[download]

Comment on Re: Putting an array into a hash gives an unexpected reference to the hash itself. Select or Download Code

Replies are listed 'Best First'.
Re^2: Putting an array into a hash gives an unexpected reference to the hash itself. by choroba (Cardinal) on Nov 08, 2012 at 15:38 UTC
I doubt Data::Dumper inspects any variable names. It just uses what you give it - or VAR1, VAR2 if it gets nothing. لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply]
Re^3: Putting an array into a hash gives an unexpected reference to the hash itself. by AnomalousMonk (Archbishop) on Nov 08, 2012 at 19:49 UTC
I doubt Data::Dumper inspects any variable names. It doesn't (as far as I know), and my code example would have been clearer had I not supplied a variable name to `Dump()` in contrast to the OP. I just wanted to make the points that `Data::Dumper` tries to emphasize repeated references within the data structure it's dumping (as these are usually important), and that even if one could sometimes recover the name of a reference, it probably wouldn't be worth doing.	[reply] [d/l] [select]

In Section Seekers of Perl Wisdom