Sorry, I don't understand. Dereferencing in that way would be a "useless use of exists". To make it not break, you'd simply write: my $bar = ${exists $foo{'bar'} or \undef }; But that is exactly the same as my $bar = $foo{'bar'}; Neither of them vivifies anything. Autovivification takes places only for multilevel deref: my $bar = $foo{'bar'}{'baz'}; Now there will be a bar key in %foo indexing an empty hashref, even if none was there before. A baz key, again, will not be vivified into this new %{$foo{'bar'}} hash. Note that, again, the same will happen if you try this: my $bar = ${exist $foo{'bar'}{'baz'} or \undef}; But the new exists semantic could be used to simplify writing a truly non-vivifying multilevel deref: 
my $qux = \%foo;
$qux = exists $qux->{$_} or (undef $qux, last)
    for qw(bar baz quux qux);

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Makeshifts last the longest.

In reply to Re^2: optimization - exists should return a reference by Aristotle
in thread optimization - exists should return a reference by John M. Dlugosz

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