package Output_Strategy::HTML; package Output_Strategy::CSV; . . . my $output_strategy = $opt{'html'} ? 'Output_Strategy::HTML' : 'Output_Strategy::CSV'; $output_strategy->preamble; $output_strategy->render(@data); $output_strategy->postamble; # whatever #### package Foo; use base 'Output_Strategy'; # this is a 'strategy handle class' . . . # set the inheritance path at run time: @Output_Strategy::ISA = ( $opt{'html'} ? 'Output_Strategy::HTML' : 'Output_Strategy::CSV' );