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.
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
