hash of objects inside an instance

Hi,

I have two classes : Employee and Department
every Employee works for at least one department. Sometimes the cost is distributed over 2 or more departments. So I'd want a hashref inside the Employee in which the keys are Department instances and the value a percentage to be attributed to that Department.

I tried as follow:

    package Employee;

    has 'departments' => (is=>'ro', isa=>'hashref[Department]', default=>{{}});

(I used traits also, but that doesn't really change the problem...)

so know I can use:

    $an_employee -> departments -> {$a_department} = 100;

and also use the same for retrieving the value, which works.

The content of the $an_employee -> departments is a hash containing keys like:
'Department=HASH(0x7fa823c87b48)'

What bothers me then is that I can't use this string as a Department object and i.e. send a message to a key object of the departments hashref of an Employee.

How can I achieve this ?
--
erik