[PATCH] Replace __gnu_cxx::__ops::__negate with std::not_fn

[François Dumont]

On 22/05/2023 22:55, Jonathan Wakely wrote:
>
>
> On Mon, 22 May 2023 at 21:51, François Dumont via Libstdc++ 
> <libstdc++@gcc.gnu.org <mailto:libstdc%2B%2B@gcc.gnu.org>> wrote:
>
>     I was thinking that it might be nice to get rid of
>     predefined_ops.h content.
>
>     So here is a start with __negate. Drawback is that stl_algo.h has to
>     include <functional>.
>
>
> We definitely don't want that. std::not_fn could be move to its own 
> header.
>
> But I'm not sure this is a good change anyway, as we can't do it 
> unconditionally. Pre-C++17 code would still be using the 
> predefined_ops.h function objects, so we can't remove that code. And 
> we'll get template bloat from instantiating the algos twice, once with 
> the old function objects and once with std::not_fn.

True, what do you advise then ? Should I just forget about it ? 
Introduce a std::__not_fn for pre-C++17 ?

I am studying this last proposal, let me know if it is just impossible 
or a waste of time.

>
>     For now I just get rid of stl_algo.h include in
>     <functional> to rather use stl_algobase.h. But maybe it would be
>     better
>     to also isolate std::not_fn in a dedicated header file so that
>     stl_algo.h do not have to include all <functional>.
>
>          libstdc++: Replace __gnu_cxx::__ops::__negate with std::not_fn
>
>          Replace the internal __gnu_cxx::__ops::__negate function and
>     associated
>          __gnu_cxx::__ops::_Iter_negate by the C++17 std::not_fn.
>
>          libstdc++-v3/ChangeLog:
>
>                  * include/bits/predefined_ops.h: Include <version>.
>
>
> No, please don't include <version> anywhere. If you do that, it means 
> <functional> now defines every feature test macro in the entire 
> library, which makes it look like you can get smart pointers and 
> ranges and constexpr math all from <functional>.

Ok, I wasn't aware about the interest of <version>. I see now, limited 
to user code.

I'm testing only the move of std::search to stl_algobase.h to avoid 
stl_algo.h include in <functional>. I'll submit it later.