Re: The new Boost 17.0.0

From: Edward Diener (eldiener_at_[hidden])
Date: 2020-12-02 14:20:32

On 12/2/2020 4:03 AM, Alexander Grund via Boost wrote:
> 
>> That's not what I have in mind. Macros don't solve the problem. What I 
>> have in mind is that there is a single library that, in its interface, 
>> can seamlessly take either boost::fs::path or std::fs::path, without 
>> the user having to define anything.
>>
>> Of course, when building the library, you probably would need to have 
>> Boost.Filesystem available.
> 
> This may work for simple types like string_view. But it won't work for 
> (non-header-only) libraries using e.g. fs::path. At some point you have 
> to convert to either type or to a third and that is gonna cost you
> 
> Additionally that interface may need includes to either or would require 
> the user to include that first introducing an include-order issue.
> 
> And finally once you return a type you have no way for "either" (again 
> except for simple types that could on-the-fly convert) and that too 
> requires an explicit choice for the include.
> 
> IMO it would be enough on a cost-benefit ratio to go to C++11 by 
> basically banning the use of MPL in Boost (the single-worst offender on 
> compile times) and reducing the use of type_traits to the absolute 
> minimum. Those 2 are (transitively) in the largest chunk of boost 
> libraries and hence hit hard on compiletimes. Then using the std 
> smart-pointers wherever possible would further untangle the libraries. 
> So basically a bottom-up approach to improvement instead of a fork to 
> whatever is the current greatest and latest. This could even be done 
> for/by GSoC, interns or similar. And in ~8 years one can check if C++17 
> would be a good base point.

Feel free to offer PRs to those C++98/C++03 libraries to transition them 
from MPL to mp11 and from Boost type traits to standard type traits so 
that they can become C++11 libraries. I do have the greatest admiration 
for mp11 so I am not being facetious. But "banning" MPL and Boost type 
traits is going to currently remove a great number of libraries from 
Boost. I do agree that a bottom up approach is necessary to transition 
Boost libraries to C++11 since a given Boost C++98/C++03 library has 
dependencies on other Boost C++98/C++03 which themselves use the Boost 
rather than the equivalent standard library.