problems dereferencing an array of arrays as a hash value

jasonl has asked for the wisdom of the Perl Monks concerning the following question:

Using Net::LDAP, I'm running into a problem trying to deal with multiple instances of an attribute. It appears that they get stored in a hash as an array of arrays; in the initial hash ($valref), I can dump the values like this:

@pktClassList = @$valref{packetclassifierlist};
print "class = ";
foreach my $i (@pktClassList) {
  foreach my $j (@$i) {
    print "$j\n";
  }
}
[download]

Unfortunately I need to get @pktClassList to another sub as a member of a different hash. I'm assigning it to the hash in a switch statement like this:

...
case /packetclassifierlist/    { $tlvHash{pktClassList} = "@pktClassLi
+st" }
...
[download]

I then pass $tlvHash to my new sub as "newSub($tlv,%tlvHash);". In newSub I'm doing this:

...
my ($tlv, %tlvHash) = @_;
...
my $classArray = $tlvHash{pktClassList};

foreach my $i (@$classArray) {
  print "i = $i\n";
  foreach my $j (@$i) {
    print "j = $j\n";
  }
}
[download]

I've tried various permutations of @, $, and @$ around classArray and tlvHash, but if the code executes at all, the best I get is "Can't use string ("ARRAY(0xa3f6e4)") as an ARRAY ref while "strict refs" in use...." I'm really trying to stick with packing this into %tlvHash instead of passing it as a separate arg, because multiple functions are calling newSub and they won't all have this attribute.

Comment on problems dereferencing an array of arrays as a hash value Select or Download Code

Replies are listed 'Best First'.
Re: problems dereferencing an array of arrays as a hash value by gmargo (Hermit) on Nov 23, 2009 at 16:54 UTC
How about a new array reference, like this? `case /packetclassifierlist/ { $tlvHash{pktClassList} = [ @pktClassL +ist ] }` [download]	[reply] [d/l]
Re^2: problems dereferencing an array of arrays as a hash value by jasonl (Acolyte) on Nov 23, 2009 at 17:14 UTC
Thanks! That did it, but I'm not quite clear why. Can you explain a little what's going on there?	[reply]
Re^3: problems dereferencing an array of arrays as a hash value by gmargo (Hermit) on Nov 23, 2009 at 17:42 UTC
The brackets `[]` create a reference to an anonymous array. With an array inside the brackets like `[ @pktClassList ]`, the contents of the `@pktClassList` array are copied into the new anonymous array. There is a different way to get the same effect, but which avoids the second copy. If the `@pktClassList` array is a local variable in a subroutine, which gets used only once before going out of scope, then you could have used the `@pktClassList` array directly like this: `case /packetclassifierlist/ { $tlvHash{pktClassList} = \@pktClassLi +st }` [download] The key is the scope of the original `@pktClassList` array - when the variable goes out of scope, it becomes an anonymous array by virtue of being referenced by the `%tlvHash` hash. Quite unlike the C language. See perlref for more info on references. Anonymous arrays are addressed early in the document.	[reply] [d/l] [select]
Re: problems dereferencing an array of arrays as a hash value by toolic (Bishop) on Nov 23, 2009 at 16:54 UTC
I'm having a hard time understanding your question, but a few things look suspicious: `{ $tlvHash{pktClassList} = "@pktClassList" }` [download] Do you really want to inject spaces between array elements here? If not, get rid of the quotes. Try to eliminate the switch/case statement for debugging purposes, as Switch has many unusual side-effects. Show your data using Data::Dumper. That might clarify things: `use Data::Dumper; print Dumper(\%tlvHash);` [download]	[reply] [d/l] [select]
Re^2: problems dereferencing an array of arrays as a hash value by Anonymous Monk on Nov 24, 2009 at 10:23 UTC
If he gets rid of quotes, he gets number of elements :)	[reply]