I've used my subclass package name as a key to a child hash. So while my parent may say $self->{ 'key' } internally, I say $self->{ +__PACKAGE__ }{ 'key' } which works as long as my parent doesn't name their hash keys things like Foo::Bar.

# A "dumping" of such a structure.
$self = {
    bar => ...,
    foo => ...,
    'Foo::Bar' => {
        bar => ...,
        foo => ... } }
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