On Tue, 12 Sept 2023 at 13:46, Patrick Palka via Libstdc++ <libstd...@gcc.gnu.org> wrote: > > On Mon, 11 Sep 2023, Patrick Palka wrote: > > > This specialization for the case of no bound args, added by > > r13-4214-gcbd05ca5ab1231, seems to be mostly obsoleted by > > r13-5033-ge2eab3c4edb6aa which added [[no_unique_address]] to the > > main template's data members. And the compile time advantage of > > avoiding an empty tuple and index_sequence seems minimal. Removing this > > specialization also means we don't have to fix the PR111327 bug in > > another place. > > FWIW I don't feel strongly about removing this specialization. If we > keep it We'd at least be able to reuse it for std::bind_back, and it > wouldn't be hard to fix the PR111327 bug in its implementation.
Yeah, I'm ambivalent. But since you've got a patch to fix 111327 ready which doesn't include this specialization, let's remove it. The empty std::tuple is at least already explicitly specialized, so I agree its overhead probably isn't very significant. OK for trunk. I'm not sure if we should change it in gcc-13 now though. > > > > > PR libstdc++/111327 > > > > libstdc++-v3/ChangeLog: > > > > * include/std/functional (_Bind_front0): Remove. > > (_Bind_front_t): Adjust. > > --- > > libstdc++-v3/include/std/functional | 63 +---------------------------- > > 1 file changed, 1 insertion(+), 62 deletions(-) > > > > diff --git a/libstdc++-v3/include/std/functional > > b/libstdc++-v3/include/std/functional > > index 60d4d1f3dd2..7d1b890bb4e 100644 > > --- a/libstdc++-v3/include/std/functional > > +++ b/libstdc++-v3/include/std/functional > > @@ -996,69 +996,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > [[no_unique_address]] std::tuple<_BoundArgs...> _M_bound_args; > > }; > > > > - // Avoid the overhead of an empty tuple<> if there are no bound args. > > - template<typename _Fd> > > - struct _Bind_front0 > > - { > > - static_assert(is_move_constructible_v<_Fd>); > > - > > - // First parameter is to ensure this constructor is never used > > - // instead of the copy/move constructor. > > - template<typename _Fn> > > - explicit constexpr > > - _Bind_front0(int, _Fn&& __fn) > > - noexcept(is_nothrow_constructible_v<_Fd, _Fn>) > > - : _M_fd(std::forward<_Fn>(__fn)) > > - { } > > - > > - _Bind_front0(const _Bind_front0&) = default; > > - _Bind_front0(_Bind_front0&&) = default; > > - _Bind_front0& operator=(const _Bind_front0&) = default; > > - _Bind_front0& operator=(_Bind_front0&&) = default; > > - ~_Bind_front0() = default; > > - > > - template<typename... _CallArgs> > > - constexpr > > - invoke_result_t<_Fd&, _CallArgs...> > > - operator()(_CallArgs&&... __call_args) & > > - noexcept(is_nothrow_invocable_v<_Fd&, _CallArgs...>) > > - { return std::invoke(_M_fd, std::forward<_CallArgs>(__call_args)...); > > } > > - > > - template<typename... _CallArgs> > > - constexpr > > - invoke_result_t<const _Fd&, _CallArgs...> > > - operator()(_CallArgs&&... __call_args) const & > > - noexcept(is_nothrow_invocable_v<const _Fd&, _CallArgs...>) > > - { return std::invoke(_M_fd, std::forward<_CallArgs>(__call_args)...); > > } > > - > > - template<typename... _CallArgs> > > - constexpr > > - invoke_result_t<_Fd, _CallArgs...> > > - operator()(_CallArgs&&... __call_args) && > > - noexcept(is_nothrow_invocable_v<_Fd, _CallArgs...>) > > - { > > - return std::invoke(std::move(_M_fd), > > - std::forward<_CallArgs>(__call_args)...); > > - } > > - > > - template<typename... _CallArgs> > > - constexpr > > - invoke_result_t<const _Fd, _CallArgs...> > > - operator()(_CallArgs&&... __call_args) const && > > - noexcept(is_nothrow_invocable_v<const _Fd, _CallArgs...>) > > - { > > - return std::invoke(std::move(_M_fd), > > - std::forward<_CallArgs>(__call_args)...); > > - } > > - > > - private: > > - [[no_unique_address]] _Fd _M_fd; > > - }; > > - > > template<typename _Fn, typename... _Args> > > - using _Bind_front_t > > - = __conditional_t<sizeof...(_Args) == 0, _Bind_front0<decay_t<_Fn>>, > > - _Bind_front<decay_t<_Fn>, decay_t<_Args>...>>; > > + using _Bind_front_t = _Bind_front<decay_t<_Fn>, decay_t<_Args>...>; > > > > /** Create call wrapper by partial application of arguments to function. > > * > > -- > > 2.42.0.158.g94e83dcf5b > > > > >