| Message ID | 20230414194512.2569383-1-ppalka@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] libstdc++: Convert _RangeAdaptorClosure into a CRTP class [PR108827] | expand |
On Fri, 14 Apr 2023, Patrick Palka wrote: > Using the CRTP idiom for this base class avoids bloating the size of a > pipeline when adding distinct empty range adaptor closure objects to it, > as detailed in section 4.1 of P2387R3. > > But it means we can no longer define its operator| overloads as hidden > friends, since each instantiation of _RangeAdaptorClosure would then > introduce its own logically different hidden friends. So for example > during overload resolution for the outer pipe operator in > > :x | (views::reverse | views::join) > > we'd have to consider 6 different hidden operator| friends: > > 2 from _RangeAdaptorClosure<_Reverse> > 2 from _RangeAdaptorClosure<_Join> > 2 from _RangeAdaptorClosure<_Pipe<_Reverse, _Join>> > > which is wasteful and can even cause hard errors in some cases. So we > instead define the operator| overloads at namespace scope in an isolated > namespace. On second thought, since this doesn't fix a bug or add new functionality it seems more like GCC 14 material. The size reduction is nice but it's probably not a big deal in practice since adaptor pipelines are usually very transient objects that don't get passed around as function arguments etc. But perhaps the second patch implementing range_adaptor_closure would be desirable for GCC 13? I'll post an updated standalone version of that patch for separate consideration. > > PR libstdc++/108827 > > libstdc++-v3/ChangeLog: > > * include/std/ranges (__adaptor::_RangeAdaptorClosure): Move ... > (__adaptor::__closure::_RangeAdaptorClosure): ... here and turn > it into a CRTP class template. Move hidden operator| friends > into namespace scope and adjust their constraints. Add a > using-declaration for this at __adaptor::_RangeAdaptorClosure. > (__closure::__is_range_adaptor_closure_fn): Define. > (__closure::__is_range_adaptor_closure): Define. > (__adaptor::_Partial): Adjust use of _RangeAdaptorClosure. > (__adaptor::_Pipe): Likewise. > (views::_All): Likewise. > (views::_Join): Likewise. > (views::_Common): Likewise. > (views::_Reverse): Likewise. > (views::_Elements): Likewise. > (views::_Adjacent): Likewise. > (views::_AsRvalue): Likewise. > (views::_Enumerate): Likewise. > (views::_AsConst): Likewise. > * testsuite/std/ranges/adaptors/all.cc: Reintroduce > static_assert expecting that adding empty range adaptor > closure objects to a pipeline doesn't increase the size of a > pipeline. > --- > libstdc++-v3/include/std/ranges | 69 +++++++++++-------- > .../testsuite/std/ranges/adaptors/all.cc | 7 -- > 2 files changed, 42 insertions(+), 34 deletions(-) > > diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges > index 283d757faa4..531ec6f68b3 100644 > --- a/libstdc++-v3/include/std/ranges > +++ b/libstdc++-v3/include/std/ranges > @@ -872,30 +872,45 @@ namespace views::__adaptor > template<typename _Lhs, typename _Rhs> > struct _Pipe; > > - // The base class of every range adaptor closure. > - // > - // The derived class should define the optional static data member > - // _S_has_simple_call_op to true if the behavior of this adaptor is > - // independent of the constness/value category of the adaptor object. > - struct _RangeAdaptorClosure > + namespace __closure > { > + // The base class of every range adaptor closure. > + // > + // The derived class should define the optional static data member > + // _S_has_simple_call_op to true if the behavior of this adaptor is > + // independent of the constness/value category of the adaptor object. > + template<typename _Derived> > + struct _RangeAdaptorClosure > + { }; > + > + template<typename _Tp, typename _Up> > + requires (!same_as<_Tp, _RangeAdaptorClosure<_Up>>) > + void __is_range_adaptor_closure_fn > + (const _Tp&, const _RangeAdaptorClosure<_Up>&); // not defined > + > + template<typename _Tp> > + concept __is_range_adaptor_closure > + = requires (_Tp __t) { __closure::__is_range_adaptor_closure_fn(__t, __t); }; > + > // range | adaptor is equivalent to adaptor(range). > template<typename _Self, typename _Range> > - requires derived_from<remove_cvref_t<_Self>, _RangeAdaptorClosure> > + requires __is_range_adaptor_closure<_Self> > && __adaptor_invocable<_Self, _Range> > - friend constexpr auto > + constexpr auto > operator|(_Range&& __r, _Self&& __self) > { return std::forward<_Self>(__self)(std::forward<_Range>(__r)); } > > // Compose the adaptors __lhs and __rhs into a pipeline, returning > // another range adaptor closure object. > template<typename _Lhs, typename _Rhs> > - requires derived_from<_Lhs, _RangeAdaptorClosure> > - && derived_from<_Rhs, _RangeAdaptorClosure> > - friend constexpr auto > + requires __is_range_adaptor_closure<_Lhs> > + && __is_range_adaptor_closure<_Rhs> > + constexpr auto > operator|(_Lhs __lhs, _Rhs __rhs) > { return _Pipe<_Lhs, _Rhs>{std::move(__lhs), std::move(__rhs)}; } > - }; > + } // namespace __closure > + > + using __closure::_RangeAdaptorClosure; > > // The base class of every range adaptor non-closure. > // > @@ -937,7 +952,7 @@ namespace views::__adaptor > // A range adaptor closure that represents partial application of > // the range adaptor _Adaptor with arguments _Args. > template<typename _Adaptor, typename... _Args> > - struct _Partial : _RangeAdaptorClosure > + struct _Partial : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>> > { > tuple<_Args...> _M_args; > > @@ -978,7 +993,7 @@ namespace views::__adaptor > // A lightweight specialization of the above primary template for > // the common case where _Adaptor accepts a single extra argument. > template<typename _Adaptor, typename _Arg> > - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure > + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>> > { > _Arg _M_arg; > > @@ -1011,7 +1026,7 @@ namespace views::__adaptor > template<typename _Adaptor, typename... _Args> > requires __adaptor_has_simple_extra_args<_Adaptor, _Args...> > && (is_trivially_copyable_v<_Args> && ...) > - struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure > + struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>> > { > tuple<_Args...> _M_args; > > @@ -1041,7 +1056,7 @@ namespace views::__adaptor > template<typename _Adaptor, typename _Arg> > requires __adaptor_has_simple_extra_args<_Adaptor, _Arg> > && is_trivially_copyable_v<_Arg> > - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure > + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>> > { > _Arg _M_arg; > > @@ -1066,7 +1081,7 @@ namespace views::__adaptor > // A range adaptor closure that represents composition of the range > // adaptor closures _Lhs and _Rhs. > template<typename _Lhs, typename _Rhs> > - struct _Pipe : _RangeAdaptorClosure > + struct _Pipe : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>> > { > [[no_unique_address]] _Lhs _M_lhs; > [[no_unique_address]] _Rhs _M_rhs; > @@ -1102,7 +1117,7 @@ namespace views::__adaptor > template<typename _Lhs, typename _Rhs> > requires __closure_has_simple_call_op<_Lhs> > && __closure_has_simple_call_op<_Rhs> > - struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure > + struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>> > { > [[no_unique_address]] _Lhs _M_lhs; > [[no_unique_address]] _Rhs _M_rhs; > @@ -1264,7 +1279,7 @@ namespace views::__adaptor > concept __can_owning_view = requires { owning_view{std::declval<_Range>()}; }; > } // namespace __detail > > - struct _All : __adaptor::_RangeAdaptorClosure > + struct _All : __adaptor::_RangeAdaptorClosure<_All> > { > template<typename _Range> > static constexpr bool > @@ -3048,7 +3063,7 @@ namespace views::__adaptor > = requires { join_view<all_t<_Range>>{std::declval<_Range>()}; }; > } // namespace __detail > > - struct _Join : __adaptor::_RangeAdaptorClosure > + struct _Join : __adaptor::_RangeAdaptorClosure<_Join> > { > template<viewable_range _Range> > requires __detail::__can_join_view<_Range> > @@ -3842,7 +3857,7 @@ namespace views::__adaptor > = requires { common_view{std::declval<_Range>()}; }; > } // namespace __detail > > - struct _Common : __adaptor::_RangeAdaptorClosure > + struct _Common : __adaptor::_RangeAdaptorClosure<_Common> > { > template<viewable_range _Range> > requires __detail::__already_common<_Range> > @@ -3963,7 +3978,7 @@ namespace views::__adaptor > = requires { reverse_view{std::declval<_Range>()}; }; > } // namespace __detail > > - struct _Reverse : __adaptor::_RangeAdaptorClosure > + struct _Reverse : __adaptor::_RangeAdaptorClosure<_Reverse> > { > template<viewable_range _Range> > requires __detail::__is_reverse_view<remove_cvref_t<_Range>> > @@ -4363,7 +4378,7 @@ namespace views::__adaptor > } // namespace __detail > > template<size_t _Nm> > - struct _Elements : __adaptor::_RangeAdaptorClosure > + struct _Elements : __adaptor::_RangeAdaptorClosure<_Elements<_Nm>> > { > template<viewable_range _Range> > requires __detail::__can_elements_view<_Nm, _Range> > @@ -5484,7 +5499,7 @@ namespace views::__adaptor > } > > template<size_t _Nm> > - struct _Adjacent : __adaptor::_RangeAdaptorClosure > + struct _Adjacent : __adaptor::_RangeAdaptorClosure<_Adjacent<_Nm>> > { > template<viewable_range _Range> > requires (_Nm == 0) || __detail::__can_adjacent_view<_Nm, _Range> > @@ -8609,7 +8624,7 @@ namespace views::__adaptor > concept __can_as_rvalue_view = requires { as_rvalue_view(std::declval<_Tp>()); }; > } > > - struct _AsRvalue : __adaptor::_RangeAdaptorClosure > + struct _AsRvalue : __adaptor::_RangeAdaptorClosure<_AsRvalue> > { > template<viewable_range _Range> > requires __detail::__can_as_rvalue_view<_Range> > @@ -8918,7 +8933,7 @@ namespace views::__adaptor > = requires { enumerate_view<all_t<_Tp>>(std::declval<_Tp>()); }; > } > > - struct _Enumerate : __adaptor::_RangeAdaptorClosure > + struct _Enumerate : __adaptor::_RangeAdaptorClosure<_Enumerate> > { > template<viewable_range _Range> > requires __detail::__can_enumerate_view<_Range> > @@ -9004,7 +9019,7 @@ namespace views::__adaptor > concept __can_as_const_view = requires { as_const_view(std::declval<_Range>()); }; > } > > - struct _AsConst : __adaptor::_RangeAdaptorClosure > + struct _AsConst : __adaptor::_RangeAdaptorClosure<_AsConst> > { > template<viewable_range _Range> > constexpr auto > diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc > index 57cb542174b..6bbaf73a20a 100644 > --- a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc > +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc > @@ -105,12 +105,6 @@ static_assert(std::is_empty_v<decltype(views::common > | views::common > | views::keys > | views::reverse)>); > -#if 0 > -// Adding empty range adaptor closure objects to a pipeline used to not > -// increase the size of the pipeline, but now that our range adaptor closure > -// objects derive from a common empty base class, [[no_unique_address]] can no > -// longer make two empty adjacent range adaptor closure objects occupy the same > -// data member address. > static_assert(sizeof(decltype(views::take(5) | views::drop(5))) > == sizeof(decltype(views::take(5) > | views::join > @@ -119,7 +113,6 @@ static_assert(sizeof(decltype(views::take(5) | views::drop(5))) > | views::keys > | views::drop(5) > | views::reverse))); > -#endif > > template<auto all = views::all> > void > -- > 2.40.0.335.g9857273be0 > >
On Sun, Apr 16, 2023 at 11:24 PM Patrick Palka <ppalka@redhat.com> wrote: > > On Fri, 14 Apr 2023, Patrick Palka wrote: > > > Using the CRTP idiom for this base class avoids bloating the size of a > > pipeline when adding distinct empty range adaptor closure objects to it, > > as detailed in section 4.1 of P2387R3. > > > > But it means we can no longer define its operator| overloads as hidden > > friends, since each instantiation of _RangeAdaptorClosure would then > > introduce its own logically different hidden friends. So for example > > during overload resolution for the outer pipe operator in > > > > :x | (views::reverse | views::join) > > > > we'd have to consider 6 different hidden operator| friends: > > > > 2 from _RangeAdaptorClosure<_Reverse> > > 2 from _RangeAdaptorClosure<_Join> > > 2 from _RangeAdaptorClosure<_Pipe<_Reverse, _Join>> > > > > which is wasteful and can even cause hard errors in some cases. So we > > instead define the operator| overloads at namespace scope in an isolated > > namespace. > > On second thought, since this doesn't fix a bug or add new functionality > it seems more like GCC 14 material. The size reduction is nice but it's > probably not a big deal in practice since adaptor pipelines are usually > very transient objects that don't get passed around as function > arguments etc. Ping, does this look OK for trunk? > > But perhaps the second patch implementing range_adaptor_closure would be > desirable for GCC 13? I'll post an updated standalone version of that > patch for separate consideration. > > > > > PR libstdc++/108827 > > > > libstdc++-v3/ChangeLog: > > > > * include/std/ranges (__adaptor::_RangeAdaptorClosure): Move ... > > (__adaptor::__closure::_RangeAdaptorClosure): ... here and turn > > it into a CRTP class template. Move hidden operator| friends > > into namespace scope and adjust their constraints. Add a > > using-declaration for this at __adaptor::_RangeAdaptorClosure. > > (__closure::__is_range_adaptor_closure_fn): Define. > > (__closure::__is_range_adaptor_closure): Define. > > (__adaptor::_Partial): Adjust use of _RangeAdaptorClosure. > > (__adaptor::_Pipe): Likewise. > > (views::_All): Likewise. > > (views::_Join): Likewise. > > (views::_Common): Likewise. > > (views::_Reverse): Likewise. > > (views::_Elements): Likewise. > > (views::_Adjacent): Likewise. > > (views::_AsRvalue): Likewise. > > (views::_Enumerate): Likewise. > > (views::_AsConst): Likewise. > > * testsuite/std/ranges/adaptors/all.cc: Reintroduce > > static_assert expecting that adding empty range adaptor > > closure objects to a pipeline doesn't increase the size of a > > pipeline. > > --- > > libstdc++-v3/include/std/ranges | 69 +++++++++++-------- > > .../testsuite/std/ranges/adaptors/all.cc | 7 -- > > 2 files changed, 42 insertions(+), 34 deletions(-) > > > > diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges > > index 283d757faa4..531ec6f68b3 100644 > > --- a/libstdc++-v3/include/std/ranges > > +++ b/libstdc++-v3/include/std/ranges > > @@ -872,30 +872,45 @@ namespace views::__adaptor > > template<typename _Lhs, typename _Rhs> > > struct _Pipe; > > > > - // The base class of every range adaptor closure. > > - // > > - // The derived class should define the optional static data member > > - // _S_has_simple_call_op to true if the behavior of this adaptor is > > - // independent of the constness/value category of the adaptor object. > > - struct _RangeAdaptorClosure > > + namespace __closure > > { > > + // The base class of every range adaptor closure. > > + // > > + // The derived class should define the optional static data member > > + // _S_has_simple_call_op to true if the behavior of this adaptor is > > + // independent of the constness/value category of the adaptor object. > > + template<typename _Derived> > > + struct _RangeAdaptorClosure > > + { }; > > + > > + template<typename _Tp, typename _Up> > > + requires (!same_as<_Tp, _RangeAdaptorClosure<_Up>>) > > + void __is_range_adaptor_closure_fn > > + (const _Tp&, const _RangeAdaptorClosure<_Up>&); // not defined > > + > > + template<typename _Tp> > > + concept __is_range_adaptor_closure > > + = requires (_Tp __t) { __closure::__is_range_adaptor_closure_fn(__t, __t); }; > > + > > // range | adaptor is equivalent to adaptor(range). > > template<typename _Self, typename _Range> > > - requires derived_from<remove_cvref_t<_Self>, _RangeAdaptorClosure> > > + requires __is_range_adaptor_closure<_Self> > > && __adaptor_invocable<_Self, _Range> > > - friend constexpr auto > > + constexpr auto > > operator|(_Range&& __r, _Self&& __self) > > { return std::forward<_Self>(__self)(std::forward<_Range>(__r)); } > > > > // Compose the adaptors __lhs and __rhs into a pipeline, returning > > // another range adaptor closure object. > > template<typename _Lhs, typename _Rhs> > > - requires derived_from<_Lhs, _RangeAdaptorClosure> > > - && derived_from<_Rhs, _RangeAdaptorClosure> > > - friend constexpr auto > > + requires __is_range_adaptor_closure<_Lhs> > > + && __is_range_adaptor_closure<_Rhs> > > + constexpr auto > > operator|(_Lhs __lhs, _Rhs __rhs) > > { return _Pipe<_Lhs, _Rhs>{std::move(__lhs), std::move(__rhs)}; } > > - }; > > + } // namespace __closure > > + > > + using __closure::_RangeAdaptorClosure; > > > > // The base class of every range adaptor non-closure. > > // > > @@ -937,7 +952,7 @@ namespace views::__adaptor > > // A range adaptor closure that represents partial application of > > // the range adaptor _Adaptor with arguments _Args. > > template<typename _Adaptor, typename... _Args> > > - struct _Partial : _RangeAdaptorClosure > > + struct _Partial : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>> > > { > > tuple<_Args...> _M_args; > > > > @@ -978,7 +993,7 @@ namespace views::__adaptor > > // A lightweight specialization of the above primary template for > > // the common case where _Adaptor accepts a single extra argument. > > template<typename _Adaptor, typename _Arg> > > - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure > > + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>> > > { > > _Arg _M_arg; > > > > @@ -1011,7 +1026,7 @@ namespace views::__adaptor > > template<typename _Adaptor, typename... _Args> > > requires __adaptor_has_simple_extra_args<_Adaptor, _Args...> > > && (is_trivially_copyable_v<_Args> && ...) > > - struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure > > + struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>> > > { > > tuple<_Args...> _M_args; > > > > @@ -1041,7 +1056,7 @@ namespace views::__adaptor > > template<typename _Adaptor, typename _Arg> > > requires __adaptor_has_simple_extra_args<_Adaptor, _Arg> > > && is_trivially_copyable_v<_Arg> > > - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure > > + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>> > > { > > _Arg _M_arg; > > > > @@ -1066,7 +1081,7 @@ namespace views::__adaptor > > // A range adaptor closure that represents composition of the range > > // adaptor closures _Lhs and _Rhs. > > template<typename _Lhs, typename _Rhs> > > - struct _Pipe : _RangeAdaptorClosure > > + struct _Pipe : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>> > > { > > [[no_unique_address]] _Lhs _M_lhs; > > [[no_unique_address]] _Rhs _M_rhs; > > @@ -1102,7 +1117,7 @@ namespace views::__adaptor > > template<typename _Lhs, typename _Rhs> > > requires __closure_has_simple_call_op<_Lhs> > > && __closure_has_simple_call_op<_Rhs> > > - struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure > > + struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>> > > { > > [[no_unique_address]] _Lhs _M_lhs; > > [[no_unique_address]] _Rhs _M_rhs; > > @@ -1264,7 +1279,7 @@ namespace views::__adaptor > > concept __can_owning_view = requires { owning_view{std::declval<_Range>()}; }; > > } // namespace __detail > > > > - struct _All : __adaptor::_RangeAdaptorClosure > > + struct _All : __adaptor::_RangeAdaptorClosure<_All> > > { > > template<typename _Range> > > static constexpr bool > > @@ -3048,7 +3063,7 @@ namespace views::__adaptor > > = requires { join_view<all_t<_Range>>{std::declval<_Range>()}; }; > > } // namespace __detail > > > > - struct _Join : __adaptor::_RangeAdaptorClosure > > + struct _Join : __adaptor::_RangeAdaptorClosure<_Join> > > { > > template<viewable_range _Range> > > requires __detail::__can_join_view<_Range> > > @@ -3842,7 +3857,7 @@ namespace views::__adaptor > > = requires { common_view{std::declval<_Range>()}; }; > > } // namespace __detail > > > > - struct _Common : __adaptor::_RangeAdaptorClosure > > + struct _Common : __adaptor::_RangeAdaptorClosure<_Common> > > { > > template<viewable_range _Range> > > requires __detail::__already_common<_Range> > > @@ -3963,7 +3978,7 @@ namespace views::__adaptor > > = requires { reverse_view{std::declval<_Range>()}; }; > > } // namespace __detail > > > > - struct _Reverse : __adaptor::_RangeAdaptorClosure > > + struct _Reverse : __adaptor::_RangeAdaptorClosure<_Reverse> > > { > > template<viewable_range _Range> > > requires __detail::__is_reverse_view<remove_cvref_t<_Range>> > > @@ -4363,7 +4378,7 @@ namespace views::__adaptor > > } // namespace __detail > > > > template<size_t _Nm> > > - struct _Elements : __adaptor::_RangeAdaptorClosure > > + struct _Elements : __adaptor::_RangeAdaptorClosure<_Elements<_Nm>> > > { > > template<viewable_range _Range> > > requires __detail::__can_elements_view<_Nm, _Range> > > @@ -5484,7 +5499,7 @@ namespace views::__adaptor > > } > > > > template<size_t _Nm> > > - struct _Adjacent : __adaptor::_RangeAdaptorClosure > > + struct _Adjacent : __adaptor::_RangeAdaptorClosure<_Adjacent<_Nm>> > > { > > template<viewable_range _Range> > > requires (_Nm == 0) || __detail::__can_adjacent_view<_Nm, _Range> > > @@ -8609,7 +8624,7 @@ namespace views::__adaptor > > concept __can_as_rvalue_view = requires { as_rvalue_view(std::declval<_Tp>()); }; > > } > > > > - struct _AsRvalue : __adaptor::_RangeAdaptorClosure > > + struct _AsRvalue : __adaptor::_RangeAdaptorClosure<_AsRvalue> > > { > > template<viewable_range _Range> > > requires __detail::__can_as_rvalue_view<_Range> > > @@ -8918,7 +8933,7 @@ namespace views::__adaptor > > = requires { enumerate_view<all_t<_Tp>>(std::declval<_Tp>()); }; > > } > > > > - struct _Enumerate : __adaptor::_RangeAdaptorClosure > > + struct _Enumerate : __adaptor::_RangeAdaptorClosure<_Enumerate> > > { > > template<viewable_range _Range> > > requires __detail::__can_enumerate_view<_Range> > > @@ -9004,7 +9019,7 @@ namespace views::__adaptor > > concept __can_as_const_view = requires { as_const_view(std::declval<_Range>()); }; > > } > > > > - struct _AsConst : __adaptor::_RangeAdaptorClosure > > + struct _AsConst : __adaptor::_RangeAdaptorClosure<_AsConst> > > { > > template<viewable_range _Range> > > constexpr auto > > diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc > > index 57cb542174b..6bbaf73a20a 100644 > > --- a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc > > +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc > > @@ -105,12 +105,6 @@ static_assert(std::is_empty_v<decltype(views::common > > | views::common > > | views::keys > > | views::reverse)>); > > -#if 0 > > -// Adding empty range adaptor closure objects to a pipeline used to not > > -// increase the size of the pipeline, but now that our range adaptor closure > > -// objects derive from a common empty base class, [[no_unique_address]] can no > > -// longer make two empty adjacent range adaptor closure objects occupy the same > > -// data member address. > > static_assert(sizeof(decltype(views::take(5) | views::drop(5))) > > == sizeof(decltype(views::take(5) > > | views::join > > @@ -119,7 +113,6 @@ static_assert(sizeof(decltype(views::take(5) | views::drop(5))) > > | views::keys > > | views::drop(5) > > | views::reverse))); > > -#endif > > > > template<auto all = views::all> > > void > > -- > > 2.40.0.335.g9857273be0 > > > >
On Wed, 16 Aug 2023 at 17:06, Patrick Palka via Libstdc++ <libstdc++@gcc.gnu.org> wrote: > > On Sun, Apr 16, 2023 at 11:24 PM Patrick Palka <ppalka@redhat.com> wrote: > > > > On Fri, 14 Apr 2023, Patrick Palka wrote: > > > > > Using the CRTP idiom for this base class avoids bloating the size of a > > > pipeline when adding distinct empty range adaptor closure objects to it, > > > as detailed in section 4.1 of P2387R3. > > > > > > But it means we can no longer define its operator| overloads as hidden > > > friends, since each instantiation of _RangeAdaptorClosure would then > > > introduce its own logically different hidden friends. So for example > > > during overload resolution for the outer pipe operator in > > > > > > :x | (views::reverse | views::join) > > > > > > we'd have to consider 6 different hidden operator| friends: > > > > > > 2 from _RangeAdaptorClosure<_Reverse> > > > 2 from _RangeAdaptorClosure<_Join> > > > 2 from _RangeAdaptorClosure<_Pipe<_Reverse, _Join>> > > > > > > which is wasteful and can even cause hard errors in some cases. So we > > > instead define the operator| overloads at namespace scope in an isolated > > > namespace. > > > > On second thought, since this doesn't fix a bug or add new functionality > > it seems more like GCC 14 material. The size reduction is nice but it's > > probably not a big deal in practice since adaptor pipelines are usually > > very transient objects that don't get passed around as function > > arguments etc. > > Ping, does this look OK for trunk? OK for trunk, thanks. > > > > > But perhaps the second patch implementing range_adaptor_closure would be > > desirable for GCC 13? I'll post an updated standalone version of that > > patch for separate consideration. > > > > > > > > PR libstdc++/108827 > > > > > > libstdc++-v3/ChangeLog: > > > > > > * include/std/ranges (__adaptor::_RangeAdaptorClosure): Move ... > > > (__adaptor::__closure::_RangeAdaptorClosure): ... here and turn > > > it into a CRTP class template. Move hidden operator| friends > > > into namespace scope and adjust their constraints. Add a > > > using-declaration for this at __adaptor::_RangeAdaptorClosure. > > > (__closure::__is_range_adaptor_closure_fn): Define. > > > (__closure::__is_range_adaptor_closure): Define. > > > (__adaptor::_Partial): Adjust use of _RangeAdaptorClosure. > > > (__adaptor::_Pipe): Likewise. > > > (views::_All): Likewise. > > > (views::_Join): Likewise. > > > (views::_Common): Likewise. > > > (views::_Reverse): Likewise. > > > (views::_Elements): Likewise. > > > (views::_Adjacent): Likewise. > > > (views::_AsRvalue): Likewise. > > > (views::_Enumerate): Likewise. > > > (views::_AsConst): Likewise. > > > * testsuite/std/ranges/adaptors/all.cc: Reintroduce > > > static_assert expecting that adding empty range adaptor > > > closure objects to a pipeline doesn't increase the size of a > > > pipeline. > > > --- > > > libstdc++-v3/include/std/ranges | 69 +++++++++++-------- > > > .../testsuite/std/ranges/adaptors/all.cc | 7 -- > > > 2 files changed, 42 insertions(+), 34 deletions(-) > > > > > > diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges > > > index 283d757faa4..531ec6f68b3 100644 > > > --- a/libstdc++-v3/include/std/ranges > > > +++ b/libstdc++-v3/include/std/ranges > > > @@ -872,30 +872,45 @@ namespace views::__adaptor > > > template<typename _Lhs, typename _Rhs> > > > struct _Pipe; > > > > > > - // The base class of every range adaptor closure. > > > - // > > > - // The derived class should define the optional static data member > > > - // _S_has_simple_call_op to true if the behavior of this adaptor is > > > - // independent of the constness/value category of the adaptor object. > > > - struct _RangeAdaptorClosure > > > + namespace __closure > > > { > > > + // The base class of every range adaptor closure. > > > + // > > > + // The derived class should define the optional static data member > > > + // _S_has_simple_call_op to true if the behavior of this adaptor is > > > + // independent of the constness/value category of the adaptor object. > > > + template<typename _Derived> > > > + struct _RangeAdaptorClosure > > > + { }; > > > + > > > + template<typename _Tp, typename _Up> > > > + requires (!same_as<_Tp, _RangeAdaptorClosure<_Up>>) > > > + void __is_range_adaptor_closure_fn > > > + (const _Tp&, const _RangeAdaptorClosure<_Up>&); // not defined > > > + > > > + template<typename _Tp> > > > + concept __is_range_adaptor_closure > > > + = requires (_Tp __t) { __closure::__is_range_adaptor_closure_fn(__t, __t); }; > > > + > > > // range | adaptor is equivalent to adaptor(range). > > > template<typename _Self, typename _Range> > > > - requires derived_from<remove_cvref_t<_Self>, _RangeAdaptorClosure> > > > + requires __is_range_adaptor_closure<_Self> > > > && __adaptor_invocable<_Self, _Range> > > > - friend constexpr auto > > > + constexpr auto > > > operator|(_Range&& __r, _Self&& __self) > > > { return std::forward<_Self>(__self)(std::forward<_Range>(__r)); } > > > > > > // Compose the adaptors __lhs and __rhs into a pipeline, returning > > > // another range adaptor closure object. > > > template<typename _Lhs, typename _Rhs> > > > - requires derived_from<_Lhs, _RangeAdaptorClosure> > > > - && derived_from<_Rhs, _RangeAdaptorClosure> > > > - friend constexpr auto > > > + requires __is_range_adaptor_closure<_Lhs> > > > + && __is_range_adaptor_closure<_Rhs> > > > + constexpr auto > > > operator|(_Lhs __lhs, _Rhs __rhs) > > > { return _Pipe<_Lhs, _Rhs>{std::move(__lhs), std::move(__rhs)}; } > > > - }; > > > + } // namespace __closure > > > + > > > + using __closure::_RangeAdaptorClosure; > > > > > > // The base class of every range adaptor non-closure. > > > // > > > @@ -937,7 +952,7 @@ namespace views::__adaptor > > > // A range adaptor closure that represents partial application of > > > // the range adaptor _Adaptor with arguments _Args. > > > template<typename _Adaptor, typename... _Args> > > > - struct _Partial : _RangeAdaptorClosure > > > + struct _Partial : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>> > > > { > > > tuple<_Args...> _M_args; > > > > > > @@ -978,7 +993,7 @@ namespace views::__adaptor > > > // A lightweight specialization of the above primary template for > > > // the common case where _Adaptor accepts a single extra argument. > > > template<typename _Adaptor, typename _Arg> > > > - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure > > > + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>> > > > { > > > _Arg _M_arg; > > > > > > @@ -1011,7 +1026,7 @@ namespace views::__adaptor > > > template<typename _Adaptor, typename... _Args> > > > requires __adaptor_has_simple_extra_args<_Adaptor, _Args...> > > > && (is_trivially_copyable_v<_Args> && ...) > > > - struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure > > > + struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>> > > > { > > > tuple<_Args...> _M_args; > > > > > > @@ -1041,7 +1056,7 @@ namespace views::__adaptor > > > template<typename _Adaptor, typename _Arg> > > > requires __adaptor_has_simple_extra_args<_Adaptor, _Arg> > > > && is_trivially_copyable_v<_Arg> > > > - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure > > > + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>> > > > { > > > _Arg _M_arg; > > > > > > @@ -1066,7 +1081,7 @@ namespace views::__adaptor > > > // A range adaptor closure that represents composition of the range > > > // adaptor closures _Lhs and _Rhs. > > > template<typename _Lhs, typename _Rhs> > > > - struct _Pipe : _RangeAdaptorClosure > > > + struct _Pipe : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>> > > > { > > > [[no_unique_address]] _Lhs _M_lhs; > > > [[no_unique_address]] _Rhs _M_rhs; > > > @@ -1102,7 +1117,7 @@ namespace views::__adaptor > > > template<typename _Lhs, typename _Rhs> > > > requires __closure_has_simple_call_op<_Lhs> > > > && __closure_has_simple_call_op<_Rhs> > > > - struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure > > > + struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>> > > > { > > > [[no_unique_address]] _Lhs _M_lhs; > > > [[no_unique_address]] _Rhs _M_rhs; > > > @@ -1264,7 +1279,7 @@ namespace views::__adaptor > > > concept __can_owning_view = requires { owning_view{std::declval<_Range>()}; }; > > > } // namespace __detail > > > > > > - struct _All : __adaptor::_RangeAdaptorClosure > > > + struct _All : __adaptor::_RangeAdaptorClosure<_All> > > > { > > > template<typename _Range> > > > static constexpr bool > > > @@ -3048,7 +3063,7 @@ namespace views::__adaptor > > > = requires { join_view<all_t<_Range>>{std::declval<_Range>()}; }; > > > } // namespace __detail > > > > > > - struct _Join : __adaptor::_RangeAdaptorClosure > > > + struct _Join : __adaptor::_RangeAdaptorClosure<_Join> > > > { > > > template<viewable_range _Range> > > > requires __detail::__can_join_view<_Range> > > > @@ -3842,7 +3857,7 @@ namespace views::__adaptor > > > = requires { common_view{std::declval<_Range>()}; }; > > > } // namespace __detail > > > > > > - struct _Common : __adaptor::_RangeAdaptorClosure > > > + struct _Common : __adaptor::_RangeAdaptorClosure<_Common> > > > { > > > template<viewable_range _Range> > > > requires __detail::__already_common<_Range> > > > @@ -3963,7 +3978,7 @@ namespace views::__adaptor > > > = requires { reverse_view{std::declval<_Range>()}; }; > > > } // namespace __detail > > > > > > - struct _Reverse : __adaptor::_RangeAdaptorClosure > > > + struct _Reverse : __adaptor::_RangeAdaptorClosure<_Reverse> > > > { > > > template<viewable_range _Range> > > > requires __detail::__is_reverse_view<remove_cvref_t<_Range>> > > > @@ -4363,7 +4378,7 @@ namespace views::__adaptor > > > } // namespace __detail > > > > > > template<size_t _Nm> > > > - struct _Elements : __adaptor::_RangeAdaptorClosure > > > + struct _Elements : __adaptor::_RangeAdaptorClosure<_Elements<_Nm>> > > > { > > > template<viewable_range _Range> > > > requires __detail::__can_elements_view<_Nm, _Range> > > > @@ -5484,7 +5499,7 @@ namespace views::__adaptor > > > } > > > > > > template<size_t _Nm> > > > - struct _Adjacent : __adaptor::_RangeAdaptorClosure > > > + struct _Adjacent : __adaptor::_RangeAdaptorClosure<_Adjacent<_Nm>> > > > { > > > template<viewable_range _Range> > > > requires (_Nm == 0) || __detail::__can_adjacent_view<_Nm, _Range> > > > @@ -8609,7 +8624,7 @@ namespace views::__adaptor > > > concept __can_as_rvalue_view = requires { as_rvalue_view(std::declval<_Tp>()); }; > > > } > > > > > > - struct _AsRvalue : __adaptor::_RangeAdaptorClosure > > > + struct _AsRvalue : __adaptor::_RangeAdaptorClosure<_AsRvalue> > > > { > > > template<viewable_range _Range> > > > requires __detail::__can_as_rvalue_view<_Range> > > > @@ -8918,7 +8933,7 @@ namespace views::__adaptor > > > = requires { enumerate_view<all_t<_Tp>>(std::declval<_Tp>()); }; > > > } > > > > > > - struct _Enumerate : __adaptor::_RangeAdaptorClosure > > > + struct _Enumerate : __adaptor::_RangeAdaptorClosure<_Enumerate> > > > { > > > template<viewable_range _Range> > > > requires __detail::__can_enumerate_view<_Range> > > > @@ -9004,7 +9019,7 @@ namespace views::__adaptor > > > concept __can_as_const_view = requires { as_const_view(std::declval<_Range>()); }; > > > } > > > > > > - struct _AsConst : __adaptor::_RangeAdaptorClosure > > > + struct _AsConst : __adaptor::_RangeAdaptorClosure<_AsConst> > > > { > > > template<viewable_range _Range> > > > constexpr auto > > > diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc > > > index 57cb542174b..6bbaf73a20a 100644 > > > --- a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc > > > +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc > > > @@ -105,12 +105,6 @@ static_assert(std::is_empty_v<decltype(views::common > > > | views::common > > > | views::keys > > > | views::reverse)>); > > > -#if 0 > > > -// Adding empty range adaptor closure objects to a pipeline used to not > > > -// increase the size of the pipeline, but now that our range adaptor closure > > > -// objects derive from a common empty base class, [[no_unique_address]] can no > > > -// longer make two empty adjacent range adaptor closure objects occupy the same > > > -// data member address. > > > static_assert(sizeof(decltype(views::take(5) | views::drop(5))) > > > == sizeof(decltype(views::take(5) > > > | views::join > > > @@ -119,7 +113,6 @@ static_assert(sizeof(decltype(views::take(5) | views::drop(5))) > > > | views::keys > > > | views::drop(5) > > > | views::reverse))); > > > -#endif > > > > > > template<auto all = views::all> > > > void > > > -- > > > 2.40.0.335.g9857273be0 > > > > > > >
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges index 283d757faa4..531ec6f68b3 100644 --- a/libstdc++-v3/include/std/ranges +++ b/libstdc++-v3/include/std/ranges @@ -872,30 +872,45 @@ namespace views::__adaptor template<typename _Lhs, typename _Rhs> struct _Pipe; - // The base class of every range adaptor closure. - // - // The derived class should define the optional static data member - // _S_has_simple_call_op to true if the behavior of this adaptor is - // independent of the constness/value category of the adaptor object. - struct _RangeAdaptorClosure + namespace __closure { + // The base class of every range adaptor closure. + // + // The derived class should define the optional static data member + // _S_has_simple_call_op to true if the behavior of this adaptor is + // independent of the constness/value category of the adaptor object. + template<typename _Derived> + struct _RangeAdaptorClosure + { }; + + template<typename _Tp, typename _Up> + requires (!same_as<_Tp, _RangeAdaptorClosure<_Up>>) + void __is_range_adaptor_closure_fn + (const _Tp&, const _RangeAdaptorClosure<_Up>&); // not defined + + template<typename _Tp> + concept __is_range_adaptor_closure + = requires (_Tp __t) { __closure::__is_range_adaptor_closure_fn(__t, __t); }; + // range | adaptor is equivalent to adaptor(range). template<typename _Self, typename _Range> - requires derived_from<remove_cvref_t<_Self>, _RangeAdaptorClosure> + requires __is_range_adaptor_closure<_Self> && __adaptor_invocable<_Self, _Range> - friend constexpr auto + constexpr auto operator|(_Range&& __r, _Self&& __self) { return std::forward<_Self>(__self)(std::forward<_Range>(__r)); } // Compose the adaptors __lhs and __rhs into a pipeline, returning // another range adaptor closure object. template<typename _Lhs, typename _Rhs> - requires derived_from<_Lhs, _RangeAdaptorClosure> - && derived_from<_Rhs, _RangeAdaptorClosure> - friend constexpr auto + requires __is_range_adaptor_closure<_Lhs> + && __is_range_adaptor_closure<_Rhs> + constexpr auto operator|(_Lhs __lhs, _Rhs __rhs) { return _Pipe<_Lhs, _Rhs>{std::move(__lhs), std::move(__rhs)}; } - }; + } // namespace __closure + + using __closure::_RangeAdaptorClosure; // The base class of every range adaptor non-closure. // @@ -937,7 +952,7 @@ namespace views::__adaptor // A range adaptor closure that represents partial application of // the range adaptor _Adaptor with arguments _Args. template<typename _Adaptor, typename... _Args> - struct _Partial : _RangeAdaptorClosure + struct _Partial : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>> { tuple<_Args...> _M_args; @@ -978,7 +993,7 @@ namespace views::__adaptor // A lightweight specialization of the above primary template for // the common case where _Adaptor accepts a single extra argument. template<typename _Adaptor, typename _Arg> - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>> { _Arg _M_arg; @@ -1011,7 +1026,7 @@ namespace views::__adaptor template<typename _Adaptor, typename... _Args> requires __adaptor_has_simple_extra_args<_Adaptor, _Args...> && (is_trivially_copyable_v<_Args> && ...) - struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure + struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>> { tuple<_Args...> _M_args; @@ -1041,7 +1056,7 @@ namespace views::__adaptor template<typename _Adaptor, typename _Arg> requires __adaptor_has_simple_extra_args<_Adaptor, _Arg> && is_trivially_copyable_v<_Arg> - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>> { _Arg _M_arg; @@ -1066,7 +1081,7 @@ namespace views::__adaptor // A range adaptor closure that represents composition of the range // adaptor closures _Lhs and _Rhs. template<typename _Lhs, typename _Rhs> - struct _Pipe : _RangeAdaptorClosure + struct _Pipe : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>> { [[no_unique_address]] _Lhs _M_lhs; [[no_unique_address]] _Rhs _M_rhs; @@ -1102,7 +1117,7 @@ namespace views::__adaptor template<typename _Lhs, typename _Rhs> requires __closure_has_simple_call_op<_Lhs> && __closure_has_simple_call_op<_Rhs> - struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure + struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>> { [[no_unique_address]] _Lhs _M_lhs; [[no_unique_address]] _Rhs _M_rhs; @@ -1264,7 +1279,7 @@ namespace views::__adaptor concept __can_owning_view = requires { owning_view{std::declval<_Range>()}; }; } // namespace __detail - struct _All : __adaptor::_RangeAdaptorClosure + struct _All : __adaptor::_RangeAdaptorClosure<_All> { template<typename _Range> static constexpr bool @@ -3048,7 +3063,7 @@ namespace views::__adaptor = requires { join_view<all_t<_Range>>{std::declval<_Range>()}; }; } // namespace __detail - struct _Join : __adaptor::_RangeAdaptorClosure + struct _Join : __adaptor::_RangeAdaptorClosure<_Join> { template<viewable_range _Range> requires __detail::__can_join_view<_Range> @@ -3842,7 +3857,7 @@ namespace views::__adaptor = requires { common_view{std::declval<_Range>()}; }; } // namespace __detail - struct _Common : __adaptor::_RangeAdaptorClosure + struct _Common : __adaptor::_RangeAdaptorClosure<_Common> { template<viewable_range _Range> requires __detail::__already_common<_Range> @@ -3963,7 +3978,7 @@ namespace views::__adaptor = requires { reverse_view{std::declval<_Range>()}; }; } // namespace __detail - struct _Reverse : __adaptor::_RangeAdaptorClosure + struct _Reverse : __adaptor::_RangeAdaptorClosure<_Reverse> { template<viewable_range _Range> requires __detail::__is_reverse_view<remove_cvref_t<_Range>> @@ -4363,7 +4378,7 @@ namespace views::__adaptor } // namespace __detail template<size_t _Nm> - struct _Elements : __adaptor::_RangeAdaptorClosure + struct _Elements : __adaptor::_RangeAdaptorClosure<_Elements<_Nm>> { template<viewable_range _Range> requires __detail::__can_elements_view<_Nm, _Range> @@ -5484,7 +5499,7 @@ namespace views::__adaptor } template<size_t _Nm> - struct _Adjacent : __adaptor::_RangeAdaptorClosure + struct _Adjacent : __adaptor::_RangeAdaptorClosure<_Adjacent<_Nm>> { template<viewable_range _Range> requires (_Nm == 0) || __detail::__can_adjacent_view<_Nm, _Range> @@ -8609,7 +8624,7 @@ namespace views::__adaptor concept __can_as_rvalue_view = requires { as_rvalue_view(std::declval<_Tp>()); }; } - struct _AsRvalue : __adaptor::_RangeAdaptorClosure + struct _AsRvalue : __adaptor::_RangeAdaptorClosure<_AsRvalue> { template<viewable_range _Range> requires __detail::__can_as_rvalue_view<_Range> @@ -8918,7 +8933,7 @@ namespace views::__adaptor = requires { enumerate_view<all_t<_Tp>>(std::declval<_Tp>()); }; } - struct _Enumerate : __adaptor::_RangeAdaptorClosure + struct _Enumerate : __adaptor::_RangeAdaptorClosure<_Enumerate> { template<viewable_range _Range> requires __detail::__can_enumerate_view<_Range> @@ -9004,7 +9019,7 @@ namespace views::__adaptor concept __can_as_const_view = requires { as_const_view(std::declval<_Range>()); }; } - struct _AsConst : __adaptor::_RangeAdaptorClosure + struct _AsConst : __adaptor::_RangeAdaptorClosure<_AsConst> { template<viewable_range _Range> constexpr auto diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc index 57cb542174b..6bbaf73a20a 100644 --- a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc @@ -105,12 +105,6 @@ static_assert(std::is_empty_v<decltype(views::common | views::common | views::keys | views::reverse)>); -#if 0 -// Adding empty range adaptor closure objects to a pipeline used to not -// increase the size of the pipeline, but now that our range adaptor closure -// objects derive from a common empty base class, [[no_unique_address]] can no -// longer make two empty adjacent range adaptor closure objects occupy the same -// data member address. static_assert(sizeof(decltype(views::take(5) | views::drop(5))) == sizeof(decltype(views::take(5) | views::join @@ -119,7 +113,6 @@ static_assert(sizeof(decltype(views::take(5) | views::drop(5))) | views::keys | views::drop(5) | views::reverse))); -#endif template<auto all = views::all> void