Which suggests two further points.
1. (More important) The reference manual should point out that {...} is the best way, overall, to deal with variadic arguments, and select is deprecated. This brings us back to the original topic.
2. (Less important) It would be nice to have a way to determine the number of variadic arguments without calling any function, something like #... as already suggested. Then a variadic function could, in principle, choose an optimal way to handle any number of arguments.
Cheers,
V.