my $session = My::Session->new();
  my $foo = Foo->new( session => $session );
  # and foo creates Bar passing session, which creates
  # Baz passing session

##</code><code>##

  my $session = My::Session->new();
  my $foo = Foo->new();

  ...
 
  package Baz;

  sub new {
   ...
   $self->{session} = My::Session->new();
  }