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

From: Peter Dimov (pdimov_at_[hidden])
Date: 2025-01-13 13:01:01

Ruben Perez wrote:
> 	In the general case (when a header also defines macros), the public
> 	header will contain both
> 
> 	import boost.mp11;
> 
> 	and the part that defines the macros, which in Mp11's case is
> 
> 	#include <boost/mp11/version.hpp>
> 
> 	User code wouldn't need to know that in addition to the import,
> 	it also needs to include a separate macro header.
> 
> 
> 
> This assumes that macros are "standalone" and don't require including any
> stdlib headers. This is the case for mp11/version.hpp and lightweight test, but
> is not for Boost.Config or Boost.Charconv headers, for instance. These may
> require including <cstddef> or <cstdint> for macros, which need to happen
> before any import std. Wouldn't this cause trouble with your scheme?

Possibly, yes. If we want to keep the public headers usable in a module unit,
we can't include <cstddef> there because it will introduce declarations.

Although whether we need to keep the headers usable in a module unit
is up for debate.

Fixing this properly can only be done on the stdlib/implementation side.