Re: Heisenberg Uncertainty Hash

You're being bitten by "autovivification". When you check to see if $hash{d}{value} exists, Perl will autovivify $hash{d} if it doesn't already exist.

Your best solution is to do if ($hash{d} and !$hash{d}{value}) { ... }.

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Re^2: Heisenberg Uncertainty Hash by DrHyde (Prior) on Apr 27, 2005 at 08:50 UTC
Instead of just checking the truth or otherwise of `$hash{d}{value}`, check for existence using the `exists()` function. That way you won't get weird bugs when the value is (eg) zero or the empty string. You might also want to check that `$hash{d}` is a reference to a hash before trying to access it.	[reply] [d/l] [select]
Re^3: Heisenberg Uncertainty Hash by Anonymous Monk on Apr 27, 2005 at 09:04 UTC
Putting an exists there, (`exists $hash{'d'}->{'value'}`) still autovivificates `$hash{'d'}`. This might be surprising, but it is logical. After all, you are enquiring about the hash `%{$hash{'d'}}` (asking whether it contains the key 'd'). Since that hash doesn't exists yet, Perl does what it always does in that case: it creates it. If you want to cover all your bases, and make sure no hash gets created as a side effect, be more explicite: `if (exists $hash{'d'} && ref $hash{'d'} eq "HASH" && exists $hash{ +'d'}->{value}) { ... }` [download]	[reply] [d/l] [select]
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