Re: [Describe] My review of Describe

From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2021-03-05 17:23:28

pt., 5 mar 2021 o 17:39 Peter Dimov via Boost <boost_at_[hidden]>
napisał(a):

> Julien Blanc wrote:
> > BOOST_DESCRIBE_STRUCT must be put outside the class definition.
> > BOOST_DESCRIBE_CLASS, on the other hand, must be put inside the class
> > definition. This is typically the "i will always get this wrong" case.
> > Since the library heavily relies on templating and macros, the error
> messages
> > are arcane to the final user. I would suggest, that, for consistency,
> > BOOST_DESCRIBE_STRUCT should be put inside the class definition as well.
>
> BOOST_DESCRIBE_CLASS goes inside the class definition for two reasons: one,
> to be able to access private members; two, to support class templates. You
> can
> do
>
> #include <boost/describe.hpp>
>
> template<class T> struct X
> {
>         T m;
>
>         BOOST_DESCRIBE_CLASS(X, (), (m), (), ())
> };
>
> int main()
> {
>         using namespace boost::describe;
>         using D = describe_members<X<int>, mod_public>;
> }
>
> (except it seems it doesn't work on MSVC 2017, which I currently use for
> unrelated reasons, but it does work on g++ and clang++ :-))
>
> In contrast, BOOST_DESCRIBE_STRUCT being put outside the struct allows
> you to describe structs whose definitions you don't control, such as
> structs
> defined in third party libraries and system headers.
>
> So there's a reason for both decisions.
>

It makes sense to support both cases. Maybe it is just the choice of names.
In C++ we are taught that struct is actually a class. Maybe a rename
BOOST_DESCRIBE_STRUCT -> BOOST_DESCRIBE_AGGREGATE (or similar) would make
the difference easier to spot.

Regards,
&rzej;