(dropping the boost-users list...) On 10/23/2012 7:27 AM, Thorsten Ottosen wrote:
On 23-10-2012 15:05, Larry Evans wrote:
However, using variadic templates may cause a slowdown in the compile times. IIRC, a variadic template version of proto was developed but was abandoned in favor of using:
http://www.boost.org/doc/libs/1_51_0/libs/preprocessor/doc/index.html
because of large compile times.
Hm.
This is really sad if variadic templates can't be used for the thing they were created for. Is this an inherent problem for large-scale use of variadic templates?
I don't want the results of my early experimentation with variadic templates to be used to draw conclusions about the feature. What Larry says is true, but in part it was due to my own naivete. Variadic templates are very good for *some* things, like perfect forwarding. Other things can be done in very tricky ways of which I was not aware at the time, like getting O(1) access to the back of a template parameter pack. And yeah, sometimes preprocessing can still improve compile-times. Without random access into a parameter pack, a data structure like std::tuple is a massive, bloated TMP hog. A fully variadic Proto *is* possible, and would probably compile faster than the non-variadic one. Creating such a library is a non-trivial undertaking, but you can see my progress thus far at: https://github.com/ericniebler/proto-0x I have only needed preprocessing to partly unroll proto::expr, which is a tuple-like data structure. I imagine that a fully variadic mpl::vector will also be problematic. -- Eric Niebler BoostPro Computing http://www.boostpro.com