use Blah;
sub new{...}
sub doSomething{ 
    my $foobar = shift;
    $foobar->someMethod(); 
    ...
}
...

##</code><code>##

use Blah;
use FooBar;

my $f = FooBar->new();
my $b = Blah->new();

$b->doSomthing( $f );