Re: Potential project: Resolving boost::chrono conflicts with std::chrono

From: Alexander Grund (alexander.grund_at_[hidden])
Date: 2019-08-09 06:48:26

Am 09.08.19 um 08:23 schrieb degski via Boost:
> On Fri, 9 Aug 2019 at 04:01, Howard Hinnant via Boost <boost_at_[hidden]>
> wrote:
>
>> The pitch:  boost::chrono, and other boost::libs needs to defer to
>> std::chrono for C++11 and later.
>>
> This library by Edward achieves the above not only for boost::chrono, but
> Boost-wide: https://github.com/eldiener/cxx_dual . From the date of the
> last commit, one can deduce, though, that this does not cover C++17 [but
> that might not be so urgent/relevant].
>
> Docs: https://eldiener.github.io/cxx_dual/doc/html/index.html .

As it was often discussed for Boost to "switch to C++11", why burden the 
maintainers with the old cruft?

My proposal would be: Implement Boost.Chrono in terms of std::chrono. 
(Just seen Atharva said the same)
This requires:
- Identify differences
- Replace Boost.Chrono types with typedefs to same std::chrono types (or 
maybe just using namespace std::chrono inside boost::chrono?)
- Adapt functions only contained in Boost.Chrono

As to "dropping C++98 compatibility" I repeat previous arguments:
- People using latest Boost probably don't use pre-C++11 compilers
- No guarantee about C++98-compatibility was ever made, each library is 
free to drop such support at any point
- This support would trickle down to dependent libraries

On the proposed alternative via cxxd: This won't work. If Boost 
internals use CXXD they will end up using either std::chrono or 
boost::chrono which will result in API and/or ABI incompatibility. 
Compare this to scoped enum usage in Boost.Filesystem in the API which 
made the library compiled in pre-C++11 mode unusable to user code in 
post-C++11 code (and vice versa) and required subsequent fixes to 
work-around that.

Alex