I was playing with XML::Simple recently, a nice module when you have small XML files. Read here for a review.

One of the options of XML::Simple is to insert an array on each hierarchy level, so it can distinguish between attributes and elements.

My first use was without that extra level, so I could access stuff just by dereferencing hashes: 

$template->{level1}->{level2}->{element1} = '1234';

[download]
It worked well until I realized, that I needed that extra level. The structure changed from something like: 
$template = {
              'level1' => {
                            'level2' => {
                                          'element1' => '1234'
                                        }
                          }
            };

[download]
to 
$template = {
              'level1' => 
                         [ 
                           {
                            'level2' => 
                                        [
                                          {
                                            'element1' => '1234'
                                          }
                                        ]
                           }
                         ]
            };

[download]
But I didn't change my program. :-(

print $template->{level1}->{level2}->{element1};

just printed nothing and

$template->{level1}->{level2}->{element1} = '1234';

gave me that wonderful error message, telling me just nothing about what happend:

Out of memory!

So when I access elements of a datastructure in the wrong way I just get undef, but when I assign to it in the wrong way Perl runs out of memory.

I think Perl should report an error, as it does when you try to use a normal hash reference as an array reference.

Is this behaviour documented somewhere?
Is it a bug?

In reply to datastructures and out of memory errors by busunsl

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