autovivification 

$ perl  -le " no autovivification qw/ strict fetch /; my $f; keys @$f;
Reference vivification forbidden at -e line 1.

$ perl  -le " no autovivification qw/ warn fetch /; my $f; keys @$f;
Reference was vivified at -e line 1.

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In reply to Re: When DOESN'T "Use of uninitialized value" show up? by Anonymous Monk
in thread When DOESN'T "Use of uninitialized value" show up? by Tim McDaniel

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