Re: [boost] Is there any interest in a library for actor programming? [preliminary submission]

Subject: Re: [boost] Is there any interest in a library for actor programming? [preliminary submission]
From: Dominik Charousset (dominik.charousset_at_[hidden])
Date: 2014-05-14 01:53:01

> On 11 May 2014, at 09:36 pm, Larry Evans wrote
> 
> Hi Dominik,
> 
> On 05/08/14 12:30, Dominik Charousset wrote post
> http://article.gmane.org/gmane.comp.lib.boost.devel/250747
> including:
> [snip]
>> 
>> [3] https://github.com/Neverlord/boost.actor/blob/a0cab41e2946df7d751c59dfead0c2122da0fb77/boost/actor/detail/int_list.hpp
> 
> However, I have a question about the implementation.
> 
> https://github.com/Neverlord/boost.actor/blob/a0cab41e2946df7d751c59dfead0c2122da0fb77/boost/actor/detail/int_list.hpp#L83
> 
> uses a recursive call using a List<typename ...Ts> which is 1 shorter
> than the argument list, List<T0, Ts...>.
> Why not just pass sizeof...(T0, Ts...):
> 
> http://en.cppreference.com/w/cpp/language/sizeof...
> 
> and keep adding indices while decreasing this sizeof value,
> as done here:
> 
> http://svn.boost.org/svn/boost/sandbox/variadic_templates/boost/mpl/package_range_c.hpp
> 
> in the package_range_c template class where:
> 
>    Start value would be 0
> and Finish value would be sizeof...(T0, Ts...)
> 
> It achieves the same result, but without producing unneeded
> instantiations.  For example:
> 
>  package_range_c<std::size_t,0,sizeof...(mpl::vector<T0,T2,T3>>::type
>  package_range_c<std::size_t,0,sizeof...(mpl::vector<S0,S2,S3>>::type
> 
> would produce 1 instantiation of:
> 
>  package_range_c<std::size_t,0,3>
> 
> whereas the int_list.hpp code would, IIUC, produce the same
> number of instantiations for the T's and S's.
> 
> Wouldn't using the sizeof... method be easier to understand
> as well as produce few instantions?

Reviewing the code again, I think there's really no good reason to recurse over Ts. Doing the unrolling in il_indices recursively with only two specializations is a simple design, but the instantiations of type_list are indeed unnecessary. Also, the dependency to type_list could be dropped when unrolling based on sizeof....

> -regards,
> Larry
> 
> NOTE:  I tried to post to the newsgroup; however, apparently my
> post got lost :(

Let's hope the list is working again...