copying array from a hash reference

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

I'm trying to write various messages across multiple lines based on the current state of my subroutine. These messages need to be placed into an array to be returned to the calling program (it has to be an array due to restrictions of the calling program). I'm using hashes of arrays to define the possible message types and want to copy one of the arrays based on a hash reference into a local array variable. The below code snippet is a generic version of what I'm trying to do:

%AniType = (cats => ["I", "like", "cats"],
            dogs => ["I", "like", "dogs"],
            none => ["I", "like", "neither"],
            both => ["I", "like", "both"],
            );

  if    ($likecats) {@AniAry = $AniType{cats} }
  elsif ($likedogs) {@AniAry = $AniType{dogs} }
  elsif ($likeboth) {@AniAry = $AniType{both} }
  else              {@AniAry = $AniType{none} }

foreach $line (0..2) {
  print "$AniAry[$line] MiscArya[$line] MiscAryb[$line] \n";
}
[download]

The problem is that @AniAry = $AniType{cats} does not result in a copy of the array. I've tried the following as well:

@AniAry = @{ $AniType{cats} };
$AniAry = $AniType{cats};
[download]

The 2nd option works if I use $AniAry->[0] but that's a reference, not an actual copy like I require. Any help is appreciated, thanks! Greg

Comment on copying array from a hash reference Select or Download Code

Replies are listed 'Best First'.
Re: copying array from a hash reference by ikegami (Patriarch) on Sep 28, 2011 at 03:13 UTC
If it's `@a` [download] with an array, it's `@{ $ar }` [download] with an array reference, so it's `@{ $AniType{cats} }` [download] in this case. Dereferencing Syntax Reference Quick Reference	[reply] [d/l] [select]
Re: copying array from a hash reference by davido (Cardinal) on Sep 28, 2011 at 02:37 UTC
You need to dereference the array-ref if you're going to copy it to a new array: `@AniAry = @{$AniType{cats}}` ...for example. perlref, perlreftut, perldsc are good sources of information. If you plan to use Perl, they're worth investing the time reading. Dave	[reply] [d/l]
Re: copying array from a hash reference by AnomalousMonk (Archbishop) on Sep 28, 2011 at 01:19 UTC
The problem is that @AniAry = $AniType{cats} does not result in a copy of the array. I've tried the following as well: `@AniAry = @{ $AniType{cats} };` `...` I don't understand what you mean in the second code example above. This works (i.e., copies the referenced array) for me: `>perl -wMstrict -le "my %AniType = ( cats => ['I', 'like', 'cats'], dogs => ['I', 'like', 'dogs'], none => ['I', 'like', 'neither'], both => ['I', 'like', 'both'], ); ;; my @AniAry = @{ $AniType{cats} }; printf qq{'$_' } for @AniAry; " 'I' 'like' 'cats'` [download]	[reply] [d/l] [select]
Re^2: copying array from a hash reference by Greg_R (Novice) on Sep 28, 2011 at 22:28 UTC
You experienced the same confusion that I did! I thought I was copying the array correctly (based on some perldocs examples). I added some additional debug code and determined that the program calling my subroutine is extremely picky in terms of the format that I return. In fact, my best option was to create and return a long string for each display line from the referenced hashes. Thanks for everyone's help; knowing I was copying / referencing correctly allowed me to focus on other areas of the code and catch the real problem.	[reply]
Re: copying array from a hash reference by onelesd (Pilgrim) on Sep 28, 2011 at 00:50 UTC
You will save yourself a lot of grief by putting `use strict; use warnings;` at the top of your script and then fixing the errors. What output are you expecting?	[reply] [d/l]