use strict;

use Tie::OneOff;

my($foo, $bar, $baz) = qw/ one two three /;

my %hash = (
  key1 => \$foo,
  key2 => \$bar,
  key3 => \$baz,
);

tie my %hash2, 'Tie::OneOff' => sub { ${ $hash{$_[0]} } };

print $hash2{key1}, "\n";

$foo = 'something else';

print $hash2{key1}, "\n";

__output__

one
something else