Re: The new Boost 17.0.0

From: Antony Polukhin (antoshkka_at_[hidden])
Date: 2020-12-01 19:44:46

On Fri, Nov 27, 2020, 15:54 Edward Diener via Boost <boost_at_[hidden]>
wrote:

> On 11/27/2020 3:58 AM, Antony Polukhin via Boost wrote:
> > Hi,
> >
> > == The problem.
> > TL;DR: we are having huge troubles with usability and popularity!
> >
> > Quite a lot of companies forbid using Boost because:
> > * it provides vocabulary types, that should be the same across the
> > whole project (like shared_ptr, filesystem::path or optional).
> > Otherwise it's hard to combine different APIs
> > * it is huge, in consists of legacy on more than a half, with a lot of
> > dependencies between libraries. This is extremely painful for big
> > companies, because there's no efficient distributed build system. Each
> > company invents it's own and/or tries to minimize headers by all
> > means.
> >
> > New companies (startups) also avoid Boost:
> > * "We are using C++17, we do not want legacy libraries with C++98
> support"
>
> If a library provides support for C++98/2003 but also works perfectly
> fine using C++17, please explain to me what is wrong with using that
> library when compiling for C++17 ? Thank you !
>

For example, that library may use boost/type_traits.hpp and boost/mpl/*.
Those headers include a bunch of text and variadic templates emulation, and
compile times getting drastically worse.

Another example: library that uses boost/optional.hpp includes ~500kB of
code. To make things funnier, ln some standard libraries inclusion of
boost/optional.hpp
leads to inclusion of <optiknal>, so removing the dependency drops 500kb of
text from each translation unit.

Final example: library work in c++98 and it almost does not depend on other
Boost libraries. Great! It's a perfect candidate for Boost17.

Nothing wrong in c++98 support, the problem is in the dependencies and huge
translation units to compile.

> * hard to upgrade, because symbols are not versioned
>

> Versioned symbols ?
>

If you are using a system package that relies on Boost, then you can not
upgrade Boost. For example mongo library uses Boost 1.45 and you wish to
use Boost 1.74 => you've got problems. Linker may merge not ABI
compatible Boost
symbols, leading to breakages. More specifically, the layout of
Boost.Variant changed multiple times since 1.45, but the signature of the
boost::apply_visitor function did not change. As a result you get
ODR-violation.

>