What if languages had a .= operator? What would it do?

To me, this operator looks analogous to other assignment operators like +=, -=, *=, /=, etc. So instead of

person = person.withAge(42);

you could write

person .= withAge(42);

But how often does this situation really happen? About as often as you need to use +=, -= or any of the other existing operation/assignment operators, in my opinion.