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

From: Edward Diener (eldiener_at_[hidden])
Date: 2019-08-09 09:09:36

On 8/9/2019 2:48 AM, Alexander Grund via Boost wrote:
> 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:Â  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.

Unless a library uses different public/protected functionality based on 
the choice between boost::chrono or std::chrono there will be no API 
incompatibility for the library itself. As far as ABI incompatibility I 
discuss in the cxxd docs how a shared library can produce different 
versions based on the cxxd choice for a dual library. For header-only 
libraries, which is a good part of Boost, ABI incompatibility does not 
exist AFAICS, but maybe I am missing what you mean when you say that.

> 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
> 
> 
> 
> 
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