Re^3: When DOESN'T "Use of uninitialized value" show up?

Actually that was exactly the case I had in mind when I made the statement. "b => {}" is required so that the presence of {c} can be checked. In fact I updated the OP's sample to include exists $x->{notdef}{notdeftoo} to demonstrate this case.

True laziness is hard work

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Re^4: When DOESN'T "Use of uninitialized value" show up? by moritz (Cardinal) on Dec 17, 2011 at 08:36 UTC
"b => {}" is required so that the presence of {c} can be checked. And that's the part where I disagree. If `$a->{b}` doesn't exist, we know that `$a->{b}{c}` cannot exist, and perl could know too. The fact that such reads autovivify are really only due to a quirk in the implementation, and not deducible from a general rule like "autovivification happens only when it needs to". Perl 6 - second systems done right	[reply] [d/l] [select]
Re^5: When DOESN'T "Use of uninitialized value" show up? by ikegami (Patriarch) on Dec 17, 2011 at 09:12 UTC
And that's the part where I disagree. If $a->{b} doesn't exist, we know that $a->{b}{c} cannot exist, But he isn't checking if `$a->{b}` exists, so it's possible that `$a->{b}{c}` can exist. Perl is being asked if `$a->{b}{c}` exists, and it's being done a few steps after autovivifying `$a->{b}`.	[reply] [d/l] [select]