CGAL users discussion list

[Marc Glisse <>]

On Fri, 28 Feb 2020, Ahmed Essam wrote:

> Hi all,
>
> I'm Ahmed Essam, and I'm interested in applying for GSoC with you this year.
>
> Regarding PR #3846 <https://github.com/CGAL/cgal/pull/3846>. As I
> understand it, the main blocker is the deprecation of `std::result_of` from
> C++20 in favor of `std::invoke_result`. I think there is a workaround that
> would work with both C++11 and C++20 when the removal happens. The main
> idea comes from this blogpost
> https://devblogs.microsoft.com/oldnewthing/20190710-00/?p=102678.
> We will use SFINAE to choose `std::invoke_of` if available, otherwise,
> choose `std::result_of`. I'm not sure is the mapping of the functionalities
> here covers all cases, but I think it's worth trying. Please find the code
> snippet below:
>
> https://gist.github.com/theartful/3dd554239743b4489b2356058f12a432
>
> If you think this might work, I can make a PR for it.

The PR you mention mostly solves the issue by using neither result_of nor 
invoke_result. CGAL only started using result_of because decltype(auto) 
didn't exist at the time.

I don't think sfinae code to detect result_of/invoke_of would help much, 
we can use __cpp_lib_is_invocable. But we should first remove most uses of 
result_of, and only then see if it makes sense to keep the few remaining 
ones as is, with a version of result_of that forwards to invoke_result, or 
if using decltype or some other constructs to remove result_of would be 
better.

(of course this is just my opinion, others may see things differently)

--
Marc Glisse