bless { hash => {} }, $class;
...
$object->{hash}->{key_inside_that};

##</code><code>##

$object->{hash}{key_inside_that},
$$object{hash}{key_inside_that},
${${$object}{hash}}{key_inside_that}

##</code><code>##

bless \{ hash => \{} }, $class;
...
${$$object->{hash}}->{key_inside_that};
${${${$object}}{hash}}{key_inside_that};
# etcetera...