No difference between exists and defined in this regard. In both cases, the *intermediate* levels will spring into existance. The last level isn't dereferenced as a hash.

If you have perl installed, you can try it out yourself:

$ perl -e 'use Data::Dump; exists $a->{foo}{bar}; dd $a;'
{ foo => {} }
$ perl -e 'use Data::Dump; defined $a->{foo}{bar}; dd $a;'
{ foo => {} }
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I guess that I'm still confused. When I look at Huck's solution, I see that short-circuit conditional expression optimization will stop the evaluation at the first "false" result. Therefore, as far as I can see, no auto-vivification would occur. My question was therefore whether it actually mattered which function-call Huck used.

Yes that is true, the function used does not matter. The solution from huck is fine. I updated my original post with a similar example.