I don't quite understand what you want. Should each class have its own %types hash, but somehow fall back to the parent's hash if something is not found? If yes, that can be implemented with methods and SUPER:: calls.

Or do you want one hash in the base class, and populate it along the way? That might look like this:

use strict;
use warnings;

{
    package Base;
    our %types = qw/BASE_TYPE Some::Class/;
    sub get_type { $types{$_[0]} }
}

{
    package Foo;
    our @ISA = qw/Base/;
    $Base::types{FOO_TYPE} =  q/Another::Class/;
}

{
    package Bar;
    our @ISA = qw/Base/;
    $Base::types{BAR_TYPE} =  q/Yet::Another::Class/;
}
use Data::Dumper;
print Dumper \%Base::types;

print Base::get_type('BAR_TYPE'), $/;
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