# untested sample code
my $a = Foo->retrieve(999); # $a is CDBI object
&some_sub('' . $a); # cast object back to scalar, here 999

##</code><code>##

# untested sample code
my $mocka = Test::MockObject->new;
$mocka->set_isa('Foo');
# ??? how to overload stringification 
# such that I can mock the result of 
# '' . $mocka
# ???