I have a hash tying package that works EXCEPT when references are returned (references as values -- not keys) and used in block dereferencing constructs like this: 

   my $h = {};
   tie %$h, "MyTie";
   $h->{KEY} = [];
   push(@{$h->{KEY}}, (qw/foo bar/));  # THIS FAILS

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The failure is: Can't use an undefined value as an ARRAY reference. Replacing the fetch line with one that does an assignment does work: 
   push(@{my $x = $h->{KEY}}, (qw/foo bar/));  # THIS WORKS!

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If I put a print statement in the Tie package's FETCH method the value is there, as expected, before it returns in all cases. That, along with it working if assigned locally first, leads me to believe this is a Perl bug. But I've found no references to any problems like this anywhere.

I've built about a half dozen similar hash ties without this problem. This tie, like some of the others, is a hash but it doesn't use itself as the data holder directly -- it refers to another anonymous hash that implements the hash being tied, kind of like this in TIEHASH: 

  sub TIEHASH
  {
      my $class = shift;

      my $self = bless({HASH_DATA => {}}, $class);

      return $self;
  }

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All the methods then use $self->{HASH_DATA} to get at the real data values being tied. The rest of the $self hash is used for housekeeping.

This Tie relies on lots of internal code so I can't post it. I also can't reproduce the problem with a smaller tie. The tie is just using other hashes behind the scenes for data normalization and validation -- no databases, files, shared memory or anything else unusual. The hash being tied is also a blessed (object) reference.

Everything else works. Nothing unusual from the debugger or using -w. It fails the same across all versions of Perl 5.5 and 5.6 I tried. I've looked at the Perl source and don't see anything there so far. I'm running on Solaris. I have not tried anywhere else yet (next on my list).

In reply to error dereferencing array in a tied hash by Anonymous Monk

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