Could you possibly be misremembering? I think creating e.g. template<F> F MyComputation(const F& x) would be allowed e.g. for supporting both float and double.

Could you possibly be misremembering? I think creating e.g. template<F> F MyComputation(const F& x) would be allowed e.g. for supporting both float and double. It would also be required when using the Ceres optimization library.