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

[Jonathan Wakely <jwakely@redhat.com>]

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On Mon, 22 May 2023 at 21:51, François Dumont via Libstdc++ <
libstdc++@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.



> 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>.



>              [__cpp_lib_not_fn](__gnu_cxx::__ops::_Iter_negate): Remove.
>              [__cpp_lib_not_fn](__gnu_cxx::__ops::__negate): Remove.
>              * include/bits/stl_algo.h: Include <functional> for C++17
> and later.
>              [__cpp_lib_not_fn](__find_if_not): Use std::not_fn.
>              (std::__search, std::search(_FwdIt1, _FwdIt1, _FwdIt2,
> _FwdIt2, _BinPred)): Move...
>              * include/bits/stl_algobase.h: ...here.
>              * include/std/functional: Replace <stl_algo.h> include by
> <stl_algobase.h>.
>
> Tests still running.
>
> François
>
>