def cook_append(self, test, refs):
        '''called by constructor and __iadd__ to avoid creating new instances.'''

        if refs is not None:
            self.crefs.append(cook_refs(refs))
            if test is not None:
                self.ctest.append(cook_test(test)) ## N.B.: -1
            else:
                self.ctest.append(None) # lens of crefs and ctest have to match
called by constructor and __iadd__ to avoid creating new instances.
torchmm/metrics/caption/cider/cider_scorer.py