Class::Factory allows you to decouple these things -- you can map a name/type to a class name and initialize a factory with them, then call 'new' on the factory and pass it the name/type and get back an object of the right type.

Here's an example, untested. (See the docs for more.)

package InvoiceCalculatorFactory;

use base qw( Class::Factory );

__PACKAGE__->add_factory_type(
         old_school => 'InvoiceCalculator::OldSchool' );
__PACKAGE__->add_factory_type(
         new_school => 'InvoiceCalculator::NewSchool' );
__PACKAGE__->add_factory_type(
        delinquent => 'InvoiceCalculator::Delinquent' );
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And then, assuming your client object has a field 'type' or something, you can do:

my $calculator = InvoiceCalculatorFactory->new( $client->type );
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Good luck!