Return the address of the specified modifiable basicAllocator or, if basicAllocator is 0, the process-wide unique (see singleton) object of this class. Note that the behavior of this function is equivalent to the following expression: ` basicAllocator ? basicAllocator : &NewDeleteAllocator::singleton() ` Also note that if a NewDeleteAllocator object is supplied, it is owned by the class and must NOT be deleted. Finally note that this method should generally not be called directly by typical clients (see bslma_default for more information).