const correctness about blasfeo HOT 2 OPEN

Thanks for the suggestion.
In general, I am against adding the const qualifier to the interfaces, for these reasons:

• in the BLAS API, there are not, since this was coded 30 years ago or so in fortran
• in the BLASFEO API, there is the possibility to alias arguments. For example dgemm_nn is defined as
  D <- alpha*A*B + beta*C
  and C and D can alias (i.e. be the same matrix), so there is not a clear distinction between inputs (A, B, C) and outputs (D). In such cases, in my opinion having no const qualifier at all is better than having something half-way (only in A and B) or 'wrong' (as it would be to add it to C in case of alias with D)

from blasfeo.

Not sure what you mean with the first point, Fortran doesn't have a notion of const and the C API definitely has const (see link in original post).

About the second point: having const in that case is a feature, not an error. const only means that you can not (and will not) alter the argument with that name. So even though C would be pointer to const and D would be a regular pointer, they can still point to the same object underneath. It provides a nice check that you are not changing the array through C but only through D. I did not think about this example before, but it is an additional argument for putting const everywhere.

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