[PATCH 1/2] libstdc++: Convert _RangeAdaptorClosure into a CRTP class [PR108827]

[PATCH 1/2] libstdc++: Convert _RangeAdaptorClosure into a CRTP class [PR108827]

[Patrick Palka]

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

[PATCH 2/2] libstdc++: Implement range_adaptor_closure from P2387R3 [PR108827]

[Patrick Palka]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

	PR libstdc++/108827

libstdc++-v3/ChangeLog:

	* include/bits/ranges_cmp.h (__cpp_lib_ranges): Bump value
	for C++23.
	* include/std/ranges (range_adaptor_closure): Define for C++23.
	* include/std/version (__cpp_lib_ranges): Bump value for
	C++23.
	* testsuite/std/ranges/version_c++23.cc: Bump expected value
	of __cpp_lib_ranges.
	* testsuite/std/ranges/range_adaptor_closure.cc: New test.
---
 libstdc++-v3/include/bits/ranges_cmp.h        |  4 ++
 libstdc++-v3/include/std/ranges               |  8 ++++
 libstdc++-v3/include/std/version              |  3 ++
 .../std/ranges/range_adaptor_closure.cc       | 42 +++++++++++++++++++
 .../testsuite/std/ranges/version_c++23.cc     |  2 +-
 5 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc

diff --git a/libstdc++-v3/include/bits/ranges_cmp.h b/libstdc++-v3/include/bits/ranges_cmp.h
index 85c1a77ccf7..6710d829a37 100644
--- a/libstdc++-v3/include/bits/ranges_cmp.h
+++ b/libstdc++-v3/include/bits/ranges_cmp.h
@@ -57,7 +57,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #ifdef __cpp_lib_concepts
 // Define this here, included by all the headers that need to define it.
+#if __cplusplus > 202002L
+#define __cpp_lib_ranges 202202L
+#else
 #define __cpp_lib_ranges 202110L
+#endif
 
 namespace ranges
 {
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 531ec6f68b3..bf3c246f95d 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1137,6 +1137,14 @@ namespace views::__adaptor
     };
 } // namespace views::__adaptor
 
+#if __cplusplus > 20202L
+  template<typename _Derived>
+    requires is_class_v<_Derived> && same_as<_Derived, remove_cv_t<_Derived>>
+    class range_adaptor_closure
+    : public views::__adaptor::_RangeAdaptorClosure<_Derived>
+    { };
+#endif
+
   template<range _Range> requires is_object_v<_Range>
     class ref_view : public view_interface<ref_view<_Range>>
     {
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 9f31f25f1e9..ad928a225ef 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -265,8 +265,10 @@
 #define __cpp_lib_interpolate 201902L
 #if __cpp_lib_concepts
 # define __cpp_lib_move_iterator_concept 202207L
+#if __cplusplus <= 202002L // N.B. updated value in C++23
 # define __cpp_lib_ranges 202110L
 #endif
+#endif
 #define __cpp_lib_shift 201806L
 
 #if _GLIBCXX_HOSTED
@@ -330,6 +332,7 @@
 #define __cpp_lib_reference_from_temporary 202202L
 #define __cpp_lib_to_underlying 202102L
 #define __cpp_lib_unreachable 202202L
+#define __cpp_lib_ranges 202202L
 #define __cpp_lib_ranges_zip 202110L
 #define __cpp_lib_ranges_chunk 202202L
 #define __cpp_lib_ranges_slide 202202L
diff --git a/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc b/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
new file mode 100644
index 00000000000..c642712ed9e
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
@@ -0,0 +1,42 @@
+// { dg-options "-std=gnu++23" }
+// { dg-do run { target c++23 } }
+
+#include <ranges>
+#include <algorithm>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+namespace views = std::views;
+
+struct _Negate : ranges::range_adaptor_closure<_Negate>
+{
+  template<ranges::viewable_range _Range>
+  constexpr auto
+  operator()(_Range&& __r) const
+  requires requires { views::transform(std::declval<_Range>(), std::negate{}); }
+  { return views::transform(std::forward<_Range>(__r), std::negate{}); }
+};
+
+constexpr _Negate negate;
+
+constexpr bool
+test01()
+{
+  int x[] = {1, 2, 3};
+  VERIFY( ranges::equal(x | negate, (int[]){-1, -2, -3}) );
+  VERIFY( ranges::equal(x | negate | negate, x) );
+  VERIFY( ranges::equal(x | (negate | negate), x) );
+  VERIFY( ranges::equal(x | views::reverse | negate, x | negate | views::reverse) );
+  VERIFY( ranges::equal(x | (views::reverse | negate), x | (negate | views::reverse)) );
+  static_assert( sizeof(negate | views::reverse | views::join) == 1 );
+  static_assert( sizeof(views::reverse | negate | views::join) == 1 );
+  static_assert( sizeof(views::reverse | views::join | negate) == 1 );
+
+  return true;
+}
+
+int
+main()
+{
+  static_assert(test01());
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
index e2c14edc8ef..90cfceb626c 100644
--- a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
+++ b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
@@ -4,7 +4,7 @@
 #include <version>
 
 #if __STDC_HOSTED__
-# if __cpp_lib_ranges != 202110L
+# if __cpp_lib_ranges != 202202L
 #  error "Feature-test macro __cpp_lib_ranges has wrong value in <version>"
 # endif
 #endif
-- 
2.40.0.335.g9857273be0

Re: [PATCH 2/2] libstdc++: Implement range_adaptor_closure from P2387R3 [PR108827]

[Patrick Palka]

On Fri, 14 Apr 2023, Patrick Palka wrote:

> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> 
> 	PR libstdc++/108827
> 
> libstdc++-v3/ChangeLog:
> 
> 	* include/bits/ranges_cmp.h (__cpp_lib_ranges): Bump value
> 	for C++23.
> 	* include/std/ranges (range_adaptor_closure): Define for C++23.
> 	* include/std/version (__cpp_lib_ranges): Bump value for
> 	C++23.
> 	* testsuite/std/ranges/version_c++23.cc: Bump expected value
> 	of __cpp_lib_ranges.
> 	* testsuite/std/ranges/range_adaptor_closure.cc: New test.

Here's a standalone version of this patch (not dependent on the first
patch in the series) it terms of the current non-CRTP representation
of _RangeAdaptorClosure:

-- >8 --

Subject: [PATCH] libstdc++: Implement range_adaptor_closure from P2387R3
 [PR108827]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

	PR libstdc++/108827

libstdc++-v3/ChangeLog:

	* include/bits/ranges_cmp.h (__cpp_lib_ranges): Bump value
	for C++23.
	* include/std/ranges (range_adaptor_closure): Define for C++23.
	* include/std/version (__cpp_lib_ranges): Bump value for
	C++23.
	* testsuite/std/ranges/version_c++23.cc: Bump expected value
	of __cpp_lib_ranges.
	* testsuite/std/ranges/range_adaptor_closure.cc: New test.
---
 libstdc++-v3/include/bits/ranges_cmp.h        |  4 ++
 libstdc++-v3/include/std/ranges               |  8 ++++
 libstdc++-v3/include/std/version              |  3 ++
 .../std/ranges/range_adaptor_closure.cc       | 46 +++++++++++++++++++
 .../testsuite/std/ranges/version_c++23.cc     |  2 +-
 5 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc

diff --git a/libstdc++-v3/include/bits/ranges_cmp.h b/libstdc++-v3/include/bits/ranges_cmp.h
index 85c1a77ccf7..6710d829a37 100644
--- a/libstdc++-v3/include/bits/ranges_cmp.h
+++ b/libstdc++-v3/include/bits/ranges_cmp.h
@@ -57,7 +57,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #ifdef __cpp_lib_concepts
 // Define this here, included by all the headers that need to define it.
+#if __cplusplus > 202002L
+#define __cpp_lib_ranges 202202L
+#else
 #define __cpp_lib_ranges 202110L
+#endif
 
 namespace ranges
 {
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 1714f3fb16c..c4d4d85bf90 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1122,6 +1122,14 @@ namespace views::__adaptor
     };
 } // namespace views::__adaptor
 
+#if __cplusplus > 202002L
+  template<typename _Derived>
+    requires is_class_v<_Derived> && same_as<_Derived, remove_cv_t<_Derived>>
+    class range_adaptor_closure
+    : public views::__adaptor::_RangeAdaptorClosure
+    { };
+#endif
+
   template<range _Range> requires is_object_v<_Range>
     class ref_view : public view_interface<ref_view<_Range>>
     {
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 027e5711ec5..02ead8f1443 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -265,8 +265,10 @@
 #define __cpp_lib_interpolate 201902L
 #if __cpp_lib_concepts
 # define __cpp_lib_move_iterator_concept 202207L
+#if __cplusplus <= 202002L // N.B. updated value in C++23
 # define __cpp_lib_ranges 202110L
 #endif
+#endif
 #define __cpp_lib_shift 201806L
 
 #if _GLIBCXX_HOSTED
@@ -330,6 +332,7 @@
 #define __cpp_lib_reference_from_temporary 202202L
 #define __cpp_lib_to_underlying 202102L
 #define __cpp_lib_unreachable 202202L
+#define __cpp_lib_ranges 202202L
 #define __cpp_lib_ranges_zip 202110L
 #define __cpp_lib_ranges_chunk 202202L
 #define __cpp_lib_ranges_slide 202202L
diff --git a/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc b/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
new file mode 100644
index 00000000000..6221f071331
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
@@ -0,0 +1,46 @@
+// { dg-options "-std=gnu++23" }
+// { dg-do run { target c++23 } }
+
+#include <ranges>
+#include <algorithm>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+namespace views = std::views;
+
+struct _Negate : ranges::range_adaptor_closure<_Negate>
+{
+  template<ranges::viewable_range _Range>
+  constexpr auto
+  operator()(_Range&& __r) const
+  requires requires { views::transform(std::declval<_Range>(), std::negate{}); }
+  { return views::transform(std::forward<_Range>(__r), std::negate{}); }
+};
+
+constexpr _Negate negate;
+
+constexpr bool
+test01()
+{
+  int x[] = {1, 2, 3};
+  VERIFY( ranges::equal(x | negate, (int[]){-1, -2, -3}) );
+  VERIFY( ranges::equal(x | negate | negate, x) );
+  VERIFY( ranges::equal(x | (negate | negate), x) );
+  VERIFY( ranges::equal(x | views::reverse | negate, x | negate | views::reverse) );
+  VERIFY( ranges::equal(x | (views::reverse | negate), x | (negate | views::reverse)) );
+#if 0
+  // These asserts currently fail for the same reason as the disabled asserts
+  // in std/ranges/adaptors/all.cc.
+  static_assert( sizeof(negate | views::reverse | views::join) == 1 );
+  static_assert( sizeof(views::reverse | negate | views::join) == 1 );
+  static_assert( sizeof(views::reverse | views::join | negate) == 1 );
+#endif
+
+  return true;
+}
+
+int
+main()
+{
+  static_assert(test01());
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
index 04609bb602c..e8342fa986a 100644
--- a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
+++ b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
@@ -4,7 +4,7 @@
 #include <version>
 
 #if __STDC_HOSTED__
-# if __cpp_lib_ranges != 202110L
+# if __cpp_lib_ranges != 202202L
 #  error "Feature-test macro __cpp_lib_ranges has wrong value in <version>"
 # endif
 #endif
-- 
2.40.0.335.g9857273be0

Re: [PATCH 2/2] libstdc++: Implement range_adaptor_closure from P2387R3 [PR108827]

[Jonathan Wakely]

[-- Attachment #1: Type: text/plain, Size: 6409 bytes --]

On Mon, 17 Apr 2023, 05:28 Patrick Palka via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> On Fri, 14 Apr 2023, Patrick Palka wrote:
>
> > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> >
> >       PR libstdc++/108827
> >
> > libstdc++-v3/ChangeLog:
> >
> >       * include/bits/ranges_cmp.h (__cpp_lib_ranges): Bump value
> >       for C++23.
> >       * include/std/ranges (range_adaptor_closure): Define for C++23.
> >       * include/std/version (__cpp_lib_ranges): Bump value for
> >       C++23.
> >       * testsuite/std/ranges/version_c++23.cc: Bump expected value
> >       of __cpp_lib_ranges.
> >       * testsuite/std/ranges/range_adaptor_closure.cc: New test.
>
> Here's a standalone version of this patch (not dependent on the first
> patch in the series) it terms of the current non-CRTP representation
> of _RangeAdaptorClosure:
>

OK, thanks for separating this from the other change.



> -- >8 --
>
> Subject: [PATCH] libstdc++: Implement range_adaptor_closure from P2387R3
>  [PR108827]
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
>
>         PR libstdc++/108827
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/ranges_cmp.h (__cpp_lib_ranges): Bump value
>         for C++23.
>         * include/std/ranges (range_adaptor_closure): Define for C++23.
>         * include/std/version (__cpp_lib_ranges): Bump value for
>         C++23.
>         * testsuite/std/ranges/version_c++23.cc: Bump expected value
>         of __cpp_lib_ranges.
>         * testsuite/std/ranges/range_adaptor_closure.cc: New test.
> ---
>  libstdc++-v3/include/bits/ranges_cmp.h        |  4 ++
>  libstdc++-v3/include/std/ranges               |  8 ++++
>  libstdc++-v3/include/std/version              |  3 ++
>  .../std/ranges/range_adaptor_closure.cc       | 46 +++++++++++++++++++
>  .../testsuite/std/ranges/version_c++23.cc     |  2 +-
>  5 files changed, 62 insertions(+), 1 deletion(-)
>  create mode 100644
> libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
>
> diff --git a/libstdc++-v3/include/bits/ranges_cmp.h
> b/libstdc++-v3/include/bits/ranges_cmp.h
> index 85c1a77ccf7..6710d829a37 100644
> --- a/libstdc++-v3/include/bits/ranges_cmp.h
> +++ b/libstdc++-v3/include/bits/ranges_cmp.h
> @@ -57,7 +57,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
>  #ifdef __cpp_lib_concepts
>  // Define this here, included by all the headers that need to define it.
> +#if __cplusplus > 202002L
> +#define __cpp_lib_ranges 202202L
> +#else
>  #define __cpp_lib_ranges 202110L
> +#endif
>
>  namespace ranges
>  {
> diff --git a/libstdc++-v3/include/std/ranges
> b/libstdc++-v3/include/std/ranges
> index 1714f3fb16c..c4d4d85bf90 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -1122,6 +1122,14 @@ namespace views::__adaptor
>      };
>  } // namespace views::__adaptor
>
> +#if __cplusplus > 202002L
> +  template<typename _Derived>
> +    requires is_class_v<_Derived> && same_as<_Derived,
> remove_cv_t<_Derived>>
> +    class range_adaptor_closure
> +    : public views::__adaptor::_RangeAdaptorClosure
> +    { };
> +#endif
> +
>    template<range _Range> requires is_object_v<_Range>
>      class ref_view : public view_interface<ref_view<_Range>>
>      {
> diff --git a/libstdc++-v3/include/std/version
> b/libstdc++-v3/include/std/version
> index 027e5711ec5..02ead8f1443 100644
> --- a/libstdc++-v3/include/std/version
> +++ b/libstdc++-v3/include/std/version
> @@ -265,8 +265,10 @@
>  #define __cpp_lib_interpolate 201902L
>  #if __cpp_lib_concepts
>  # define __cpp_lib_move_iterator_concept 202207L
> +#if __cplusplus <= 202002L // N.B. updated value in C++23
>  # define __cpp_lib_ranges 202110L
>  #endif
> +#endif
>  #define __cpp_lib_shift 201806L
>
>  #if _GLIBCXX_HOSTED
> @@ -330,6 +332,7 @@
>  #define __cpp_lib_reference_from_temporary 202202L
>  #define __cpp_lib_to_underlying 202102L
>  #define __cpp_lib_unreachable 202202L
> +#define __cpp_lib_ranges 202202L
>  #define __cpp_lib_ranges_zip 202110L
>  #define __cpp_lib_ranges_chunk 202202L
>  #define __cpp_lib_ranges_slide 202202L
> diff --git a/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
> b/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
> new file mode 100644
> index 00000000000..6221f071331
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
> @@ -0,0 +1,46 @@
> +// { dg-options "-std=gnu++23" }
> +// { dg-do run { target c++23 } }
> +
> +#include <ranges>
> +#include <algorithm>
> +#include <testsuite_hooks.h>
> +
> +namespace ranges = std::ranges;
> +namespace views = std::views;
> +
> +struct _Negate : ranges::range_adaptor_closure<_Negate>
> +{
> +  template<ranges::viewable_range _Range>
> +  constexpr auto
> +  operator()(_Range&& __r) const
> +  requires requires { views::transform(std::declval<_Range>(),
> std::negate{}); }
> +  { return views::transform(std::forward<_Range>(__r), std::negate{}); }
> +};
> +
> +constexpr _Negate negate;
> +
> +constexpr bool
> +test01()
> +{
> +  int x[] = {1, 2, 3};
> +  VERIFY( ranges::equal(x | negate, (int[]){-1, -2, -3}) );
> +  VERIFY( ranges::equal(x | negate | negate, x) );
> +  VERIFY( ranges::equal(x | (negate | negate), x) );
> +  VERIFY( ranges::equal(x | views::reverse | negate, x | negate |
> views::reverse) );
> +  VERIFY( ranges::equal(x | (views::reverse | negate), x | (negate |
> views::reverse)) );
> +#if 0
> +  // These asserts currently fail for the same reason as the disabled
> asserts
> +  // in std/ranges/adaptors/all.cc.
> +  static_assert( sizeof(negate | views::reverse | views::join) == 1 );
> +  static_assert( sizeof(views::reverse | negate | views::join) == 1 );
> +  static_assert( sizeof(views::reverse | views::join | negate) == 1 );
> +#endif
> +
> +  return true;
> +}
> +
> +int
> +main()
> +{
> +  static_assert(test01());
> +}
> diff --git a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
> b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
> index 04609bb602c..e8342fa986a 100644
> --- a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
> @@ -4,7 +4,7 @@
>  #include <version>
>
>  #if __STDC_HOSTED__
> -# if __cpp_lib_ranges != 202110L
> +# if __cpp_lib_ranges != 202202L
>  #  error "Feature-test macro __cpp_lib_ranges has wrong value in
> <version>"
>  # endif
>  #endif
> --
> 2.40.0.335.g9857273be0
>
>

Re: [PATCH 2/2] libstdc++: Implement range_adaptor_closure from P2387R3 [PR108827]

[Jonathan Wakely]

On Mon, 17 Apr 2023 at 08:26, Jonathan Wakely via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> On Mon, 17 Apr 2023, 05:28 Patrick Palka via Libstdc++, <
> libstdc++@gcc.gnu.org> wrote:
>
> > On Fri, 14 Apr 2023, Patrick Palka wrote:
> >
> > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> > >
> > >       PR libstdc++/108827
> > >
> > > libstdc++-v3/ChangeLog:
> > >
> > >       * include/bits/ranges_cmp.h (__cpp_lib_ranges): Bump value
> > >       for C++23.
> > >       * include/std/ranges (range_adaptor_closure): Define for C++23.
> > >       * include/std/version (__cpp_lib_ranges): Bump value for
> > >       C++23.
> > >       * testsuite/std/ranges/version_c++23.cc: Bump expected value
> > >       of __cpp_lib_ranges.
> > >       * testsuite/std/ranges/range_adaptor_closure.cc: New test.
> >
> > Here's a standalone version of this patch (not dependent on the first
> > patch in the series) it terms of the current non-CRTP representation
> > of _RangeAdaptorClosure:
> >
>
> OK, thanks for separating this from the other change.

I'd like RM approval to push this C++23-only change to gcc-13 as well as trunk.

>
>
>
> > -- >8 --
> >
> > Subject: [PATCH] libstdc++: Implement range_adaptor_closure from P2387R3
> >  [PR108827]
> >
> > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> >
> >         PR libstdc++/108827
> >
> > libstdc++-v3/ChangeLog:
> >
> >         * include/bits/ranges_cmp.h (__cpp_lib_ranges): Bump value
> >         for C++23.
> >         * include/std/ranges (range_adaptor_closure): Define for C++23.
> >         * include/std/version (__cpp_lib_ranges): Bump value for
> >         C++23.
> >         * testsuite/std/ranges/version_c++23.cc: Bump expected value
> >         of __cpp_lib_ranges.
> >         * testsuite/std/ranges/range_adaptor_closure.cc: New test.
> > ---
> >  libstdc++-v3/include/bits/ranges_cmp.h        |  4 ++
> >  libstdc++-v3/include/std/ranges               |  8 ++++
> >  libstdc++-v3/include/std/version              |  3 ++
> >  .../std/ranges/range_adaptor_closure.cc       | 46 +++++++++++++++++++
> >  .../testsuite/std/ranges/version_c++23.cc     |  2 +-
> >  5 files changed, 62 insertions(+), 1 deletion(-)
> >  create mode 100644
> > libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
> >
> > diff --git a/libstdc++-v3/include/bits/ranges_cmp.h
> > b/libstdc++-v3/include/bits/ranges_cmp.h
> > index 85c1a77ccf7..6710d829a37 100644
> > --- a/libstdc++-v3/include/bits/ranges_cmp.h
> > +++ b/libstdc++-v3/include/bits/ranges_cmp.h
> > @@ -57,7 +57,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >
> >  #ifdef __cpp_lib_concepts
> >  // Define this here, included by all the headers that need to define it.
> > +#if __cplusplus > 202002L
> > +#define __cpp_lib_ranges 202202L
> > +#else
> >  #define __cpp_lib_ranges 202110L
> > +#endif
> >
> >  namespace ranges
> >  {
> > diff --git a/libstdc++-v3/include/std/ranges
> > b/libstdc++-v3/include/std/ranges
> > index 1714f3fb16c..c4d4d85bf90 100644
> > --- a/libstdc++-v3/include/std/ranges
> > +++ b/libstdc++-v3/include/std/ranges
> > @@ -1122,6 +1122,14 @@ namespace views::__adaptor
> >      };
> >  } // namespace views::__adaptor
> >
> > +#if __cplusplus > 202002L
> > +  template<typename _Derived>
> > +    requires is_class_v<_Derived> && same_as<_Derived,
> > remove_cv_t<_Derived>>
> > +    class range_adaptor_closure
> > +    : public views::__adaptor::_RangeAdaptorClosure
> > +    { };
> > +#endif
> > +
> >    template<range _Range> requires is_object_v<_Range>
> >      class ref_view : public view_interface<ref_view<_Range>>
> >      {
> > diff --git a/libstdc++-v3/include/std/version
> > b/libstdc++-v3/include/std/version
> > index 027e5711ec5..02ead8f1443 100644
> > --- a/libstdc++-v3/include/std/version
> > +++ b/libstdc++-v3/include/std/version
> > @@ -265,8 +265,10 @@
> >  #define __cpp_lib_interpolate 201902L
> >  #if __cpp_lib_concepts
> >  # define __cpp_lib_move_iterator_concept 202207L
> > +#if __cplusplus <= 202002L // N.B. updated value in C++23
> >  # define __cpp_lib_ranges 202110L
> >  #endif
> > +#endif
> >  #define __cpp_lib_shift 201806L
> >
> >  #if _GLIBCXX_HOSTED
> > @@ -330,6 +332,7 @@
> >  #define __cpp_lib_reference_from_temporary 202202L
> >  #define __cpp_lib_to_underlying 202102L
> >  #define __cpp_lib_unreachable 202202L
> > +#define __cpp_lib_ranges 202202L
> >  #define __cpp_lib_ranges_zip 202110L
> >  #define __cpp_lib_ranges_chunk 202202L
> >  #define __cpp_lib_ranges_slide 202202L
> > diff --git a/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
> > b/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
> > new file mode 100644
> > index 00000000000..6221f071331
> > --- /dev/null
> > +++ b/libstdc++-v3/testsuite/std/ranges/range_adaptor_closure.cc
> > @@ -0,0 +1,46 @@
> > +// { dg-options "-std=gnu++23" }
> > +// { dg-do run { target c++23 } }
> > +
> > +#include <ranges>
> > +#include <algorithm>
> > +#include <testsuite_hooks.h>
> > +
> > +namespace ranges = std::ranges;
> > +namespace views = std::views;
> > +
> > +struct _Negate : ranges::range_adaptor_closure<_Negate>
> > +{
> > +  template<ranges::viewable_range _Range>
> > +  constexpr auto
> > +  operator()(_Range&& __r) const
> > +  requires requires { views::transform(std::declval<_Range>(),
> > std::negate{}); }
> > +  { return views::transform(std::forward<_Range>(__r), std::negate{}); }
> > +};
> > +
> > +constexpr _Negate negate;
> > +
> > +constexpr bool
> > +test01()
> > +{
> > +  int x[] = {1, 2, 3};
> > +  VERIFY( ranges::equal(x | negate, (int[]){-1, -2, -3}) );
> > +  VERIFY( ranges::equal(x | negate | negate, x) );
> > +  VERIFY( ranges::equal(x | (negate | negate), x) );
> > +  VERIFY( ranges::equal(x | views::reverse | negate, x | negate |
> > views::reverse) );
> > +  VERIFY( ranges::equal(x | (views::reverse | negate), x | (negate |
> > views::reverse)) );
> > +#if 0
> > +  // These asserts currently fail for the same reason as the disabled
> > asserts
> > +  // in std/ranges/adaptors/all.cc.
> > +  static_assert( sizeof(negate | views::reverse | views::join) == 1 );
> > +  static_assert( sizeof(views::reverse | negate | views::join) == 1 );
> > +  static_assert( sizeof(views::reverse | views::join | negate) == 1 );
> > +#endif
> > +
> > +  return true;
> > +}
> > +
> > +int
> > +main()
> > +{
> > +  static_assert(test01());
> > +}
> > diff --git a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
> > b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
> > index 04609bb602c..e8342fa986a 100644
> > --- a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
> > +++ b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
> > @@ -4,7 +4,7 @@
> >  #include <version>
> >
> >  #if __STDC_HOSTED__
> > -# if __cpp_lib_ranges != 202110L
> > +# if __cpp_lib_ranges != 202202L
> >  #  error "Feature-test macro __cpp_lib_ranges has wrong value in
> > <version>"
> >  # endif
> >  #endif
> > --
> > 2.40.0.335.g9857273be0
> >
> >
>

Re: [PATCH 2/2] libstdc++: Implement range_adaptor_closure from P2387R3 [PR108827]

[Jakub Jelinek]

On Tue, Apr 18, 2023 at 09:57:19AM +0100, Jonathan Wakely wrote:
> On Mon, 17 Apr 2023 at 08:26, Jonathan Wakely via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
> >
> > On Mon, 17 Apr 2023, 05:28 Patrick Palka via Libstdc++, <
> > libstdc++@gcc.gnu.org> wrote:
> >
> > > On Fri, 14 Apr 2023, Patrick Palka wrote:
> > >
> > > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> > > >
> > > >       PR libstdc++/108827
> > > >
> > > > libstdc++-v3/ChangeLog:
> > > >
> > > >       * include/bits/ranges_cmp.h (__cpp_lib_ranges): Bump value
> > > >       for C++23.
> > > >       * include/std/ranges (range_adaptor_closure): Define for C++23.
> > > >       * include/std/version (__cpp_lib_ranges): Bump value for
> > > >       C++23.
> > > >       * testsuite/std/ranges/version_c++23.cc: Bump expected value
> > > >       of __cpp_lib_ranges.
> > > >       * testsuite/std/ranges/range_adaptor_closure.cc: New test.
> > >
> > > Here's a standalone version of this patch (not dependent on the first
> > > patch in the series) it terms of the current non-CRTP representation
> > > of _RangeAdaptorClosure:
> > >
> >
> > OK, thanks for separating this from the other change.
> 
> I'd like RM approval to push this C++23-only change to gcc-13 as well as trunk.

Ok.

	Jakub

Re: [PATCH 1/2] libstdc++: Convert _RangeAdaptorClosure into a CRTP class [PR108827]

[Patrick Palka]

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
> 
> 

Re: [PATCH 1/2] libstdc++: Convert _RangeAdaptorClosure into a CRTP class [PR108827]

[Patrick Palka]

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
> >
> >

Re: [PATCH 1/2] libstdc++: Convert _RangeAdaptorClosure into a CRTP class [PR108827]

[Jonathan Wakely]

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
> > >
> > >
>