[boost] Re: mpl::begin<mpl::vector<...> > performance problem

From: Arkadiy Vertleyb (vertleyb_at_[hidden])
Date: 2005-03-02 12:00:07

"David Abrahams" <dave_at_[hidden]> wrote

> vector template will be expensive.  That said, I see no reason why we
> need to be causing any instantiation.  Everything *could* be done by
> partial specialization matching, though it might be verbose to account
> for the numbered and unnumbered forms.

Just speculating:

Wouldn't implementing at<> exclusively by partial specialization matching
involve defining n * n / 2 specializations?

at<v1<>, 0>, at<v2<>, 0>, at<v3<>, 0>, ..., at(Vn<>, 0)
                      at<v2<>, 1>, at<v3<>, 1>, ..., at(Vn<>, 1)
                                           at<v3<>, 2>, ..., at(Vn<>, 2)

In my case, where n = 255, this would result in ~30,000 specializations of
at (or at_impl).

Maybe this is where the actual problem is?

Regards,
Arkadiy