It means that this part of that line:  @{ $tree->{children} }[ 0 ], which is the first element of an array, pointed at by the value of the element of the hash, pointed to by $tree, and keyed by the string 'children'; is undefined -- ie. has not been set -- thus when the code tries to use that undefined value as a hash reference ->{label}, you get the error message.

All of which probably won't help you at all if you don't know Perl; even if you have some experience of other programming languages.

What you will need to determine is whether:

  1. the code that build the tree is in error and is failing to construct the tree correctly;
  2. Of if the calling code is in error; by unconditionally expecting that array element to contains a hash reference that contains a key: label.

And the first part of making that determination would be to inspect the source data from which the tree is constructed, and work out whether the undefined value should be set or not.

If, it should, then the code that constructs the tree will need correcting; if it shouldn't, the the attempt to access the undefined value should be made conditional.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority". I knew I was on the right track :)
In the absence of evidence, opinion is indistinguishable from prejudice.
I'm with torvalds on this Agile (and TDD) debunked I told'em LLVM was the way to go. But did they listen!

In reply to Re: Can't use an undefined value as a HASH reference by BrowserUk
in thread Can't use an undefined value as a HASH reference by Anonymous Monk

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