package Command;
    
    sub new {
        return (bless {}, shift);
    }
    
    sub execute {
    }
    
    package Get_normal;
    @ISA = qw( Command );
    
    sub execute {
        my ($O, $target, $key) = @_;
        $target->get_normal ($key);
        return;
    }
    
    package Data_holder;
    
    sub new {
        {...}
        
        my $g = new Get_normal;
        
        $O->{'get-funcs'} = {
            'key-1' =>  $g,
            {...}
        }
        {...}
    }
    
    sub get {
        {...}
        
        my $cmd = $O->{'get-funcs'}->{ $k } 
            || $O->{'get-funcs'}->{'get_error'}
        ;
        $result->{ $k } = $cmd->execute ( $k );
        
        {...}
    }