Re: Interest for C++20 modules support of boost officially

From: Ruben Perez (rubenperez038_at_[hidden])
Date: 2024-12-19 14:49:26

On Thu, 19 Dec 2024, 15:43 Peter Dimov via Boost, <boost_at_[hidden]>
wrote:

> Ruben Perez wrote:
> > If I understood the CMake developers and Chuanqi correctly (please let me
> > know if I didn't), you do install a library with the generated object
> files, but
> > you do not install the BMIs, as they're like pre-compiled headers.
> >
> > Let me explain how I understood it with two concrete examples. Take
> > Boost.Url as an example of a compiled library, and Boost.Regex as an
> example
> > of a header-only library.
> >
> > 1. Boost.Url today installs:
> >    * libboost_url.a, containing function definitions.
> >    * Headers, containing declarations.
> > 2. Boost.Url in the module world would install:
> >    * libboost_url.a, containing the same function definitions as above.
> >    * A boost_url.cppm file, akin to what headers are today.
> >      CMake would build a BMI from this file when a user needs to import
> > boost.url.
> >      In practice, this cppm file will likely be implemented in terms of
> the
> >      header files that we have today.
>
> Since this .cppm file will include the header files, the header files
> should also be installed in the module case.
>

Yes. And some libraries also need to export macros. These need to be
provided by traditional headers. For example, Asio needs to provide
BOOST_ASIO_HAS_LOCAL_SOCKETS.

> Where does the .cppm file go by convention? In which directory?
>

I don't think there is a convention for it yet.