I don't want to put it in an eval because that could potentially execute bottom.

Do you have a problem executing top?
$object->top->bottom
is the same as
( $object->top() )->bottom
and that executes top.

---

If the problem is that you are dealing with multiple classes, and some don't implement top and bottom, using a role/trait might make more sense (Class::Role, Class::Trait)

If the problem is that an object might not have a bottom or top sibling and returns false/undefined in those cases, the following would be better:

if ($object->top && $object->top->bottom) {
   ...
}
[download]

or

if (defined($object->top) && defined($object->top->bottom)) {
   ...
}
[download]