Thanks, but that's not what I'm after. As I said originally:

if I receive this warning in a non-trivial program, I can go back and insert some debugging code to check which one of $bar{'one'} or $foo{'one'} is unitialized.

What I want (as I said), is to have Perl automatically tell me which of the two were uninitialized within the warning, without resorting to inserting additional debug code (as is the case of using Data::Dumper)