numbers as 'generics' parameters

C++ allows integers as template parameters, so, for example I can
define a vector of size N, and verify at compile time that, say, I
don't try the inner product of a 2D (N=2) and 3D (N=3) vectors. On the
other hand, I don't have to write separate versions of my code for
various vector sizes.

As far as I can tell, Ada does not allow anything but types as
generics parameters, so what would be the approach to use with it?

a. code duplication
b. keep vector size at runtime (and check)