[libcxx][iterator] adds std::indirectly_readable and std::indirectly_writable

Implements parts of:
    * P0896R4 The One Ranges Proposal`

Depends on D99873.

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D100073

Author: cjdb

libcxx/include/__iterator/concepts.h

@@ -12,6 +12,10 @@
 
 #include <__config>
 #include <concepts>
+#include <__iterator/iter_move.h>
+#include <__iterator/incrementable_traits.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/readable_traits.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
@@ -24,18 +28,36 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if !defined(_LIBCPP_HAS_NO_RANGES)
 
-template<class _Tp>
-using __with_reference = _Tp&;
+// clang-format off
 
-template<class _Tp>
-concept __referenceable = requires {
-  typename __with_reference<_Tp>;
-};
+// [iterator.concept.readable]
+template<class _In>
+concept __indirectly_readable_impl =
+  requires(const _In __in) {
+    typename iter_value_t<_In>;
+    typename iter_reference_t<_In>;
+    typename iter_rvalue_reference_t<_In>;
+    { *__in } -> same_as<iter_reference_t<_In> >;
+    { ranges::iter_move(__in) } -> same_as<iter_rvalue_reference_t<_In> >;
+  } &&
+  common_reference_with<iter_reference_t<_In>&&, iter_value_t<_In>&> &&
+  common_reference_with<iter_reference_t<_In>&&, iter_rvalue_reference_t<_In>&&> &&
+  common_reference_with<iter_rvalue_reference_t<_In>&&, const iter_value_t<_In>&>;
 
-template<class _Tp>
-concept __dereferenceable = requires(_Tp& __t) {
-  { *__t } -> __referenceable; // not required to be equality-preserving
-};
+template<class _In>
+concept indirectly_readable = __indirectly_readable_impl<remove_cvref_t<_In> >;
+
+// [iterator.concept.writable]
+template<class _Out, class _Tp>
+concept indirectly_writable =
+  requires(_Out&& __o, _Tp&& __t) {
+    *__o = _VSTD::forward<_Tp>(__t);                        // not required to be equality-preserving
+    *_VSTD::forward<_Out>(__o) = _VSTD::forward<_Tp>(__t);  // not required to be equality-preserving
+    const_cast<const iter_reference_t<_Out>&&>(*__o) = _VSTD::forward<_Tp>(__t);                       // not required to be equality-preserving
+    const_cast<const iter_reference_t<_Out>&&>(*_VSTD::forward<_Out>(__o)) = _VSTD::forward<_Tp>(__t); // not required to be equality-preserving
+  };
+
+// clang-format on
 
 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
 

libcxx/include/__iterator/incrementable_traits.h

@@ -11,7 +11,7 @@
 #define _LIBCPP___ITERATOR_INCREMENTABLE_TRAITS_H
 
 #include <__config>
-#include <__iterator/concepts.h>
+#include <concepts>
 #include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)

libcxx/include/__iterator/iter_move.h

@@ -11,7 +11,7 @@
 #define _LIBCPP___ITERATOR_ITER_MOVE_H
 
 #include <__config>
-#include <__iterator/concepts.h>
+#include <__iterator/iterator_traits.h>
 #include <concepts> // __class_or_enum
 #include <type_traits>
 #include <utility>

libcxx/include/__iterator/iterator_traits.h

@@ -27,9 +27,23 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if !defined(_LIBCPP_HAS_NO_RANGES)
 
+template <class _Tp>
+using __with_reference = _Tp&;
+
+template <class _Tp>
+concept __referenceable = requires {
+  typename __with_reference<_Tp>;
+};
+
+template <class _Tp>
+concept __dereferenceable = requires(_Tp& __t) {
+  { *__t } -> __referenceable; // not required to be equality-preserving
+};
+
 // [iterator.traits]
 template<__dereferenceable _Tp>
 using iter_reference_t = decltype(*declval<_Tp&>());
+
 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
 
 template <class _Iter>

libcxx/include/__iterator/readable_traits.h

@@ -11,7 +11,8 @@
 #define _LIBCPP___ITERATOR_READABLE_TRAITS_H
 
 #include <__config>
-#include <__iterator/concepts.h>
+#include <concepts>
+#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header

libcxx/include/iterator

@@ -43,6 +43,15 @@ template<dereferenceable T>
   requires ...
 using iter_rvalue_reference_t = decltype(ranges::iter_move(declval<T&>())); // since C++20
 
+// [iterator.concepts], iterator concepts
+// [iterator.concept.readable], concept indirectly_­readable
+template<class In>
+  concept indirectly_readable = see below;                // since C++20
+
+// [iterator.concept.writable], concept indirectly_­writable
+template<class Out, class T>
+  concept indirectly_writable = see below;                // since C++20
+
 template<class Category, class T, class Distance = ptrdiff_t,
          class Pointer = T*, class Reference = T&>
 struct iterator

libcxx/test/std/containers/associative/map/iterator_concept_conformance.compile.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// iterator, const_iterator, reverse_iterator, const_reverse_iterator
+
+#include <map>
+
+#include <iterator>
+
+using iterator = std::map<int, int>::iterator;
+using const_iterator = std::map<int, int>::const_iterator;
+using value_type = iterator::value_type;
+
+static_assert(std::indirectly_readable<iterator>);
+static_assert(!std::indirectly_writable<iterator, value_type>);
+
+static_assert(std::indirectly_readable<const_iterator>);
+static_assert(!std::indirectly_writable<const_iterator, value_type>);

libcxx/test/std/containers/associative/multimap/iterator_concept_conformance.compile.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// iterator, const_iterator, reverse_iterator, const_reverse_iterator
+
+#include <map>
+
+#include <iterator>
+
+using iterator = std::multimap<int, int>::iterator;
+using const_iterator = std::multimap<int, int>::const_iterator;
+using value_type = iterator::value_type;
+
+static_assert(std::indirectly_readable<iterator>);
+static_assert(!std::indirectly_writable<iterator, value_type>);
+
+static_assert(std::indirectly_readable<const_iterator>);
+static_assert(!std::indirectly_writable<const_iterator, value_type>);

libcxx/test/std/containers/associative/multiset/iterator_concept_conformance.compile.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// iterator, const_iterator, reverse_iterator, const_reverse_iterator
+
+#include <set>
+
+#include <iterator>
+
+using iterator = std::multiset<int>::iterator;
+using const_iterator = std::multiset<int>::const_iterator;
+using value_type = iterator::value_type;
+
+static_assert(std::indirectly_readable<iterator>);
+static_assert(!std::indirectly_writable<iterator, value_type>);
+
+static_assert(std::indirectly_readable<const_iterator>);
+static_assert(!std::indirectly_writable<const_iterator, value_type>);

libcxx/test/std/containers/associative/set/iterator_concept_conformance.compile.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// iterator, const_iterator, reverse_iterator, const_reverse_iterator
+
+#include <set>
+
+#include <iterator>
+
+using iterator = std::set<int>::iterator;
+using const_iterator = std::set<int>::const_iterator;
+using value_type = iterator::value_type;
+
+static_assert(std::indirectly_readable<iterator>);
+static_assert(!std::indirectly_writable<iterator, value_type>);
+
+static_assert(std::indirectly_readable<const_iterator>);
+static_assert(!std::indirectly_writable<const_iterator, value_type>);

libcxx/test/std/containers/sequences/array/iterator_concept_conformance.compile.pass.cpp

@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// iterator, const_iterator, reverse_iterator, const_reverse_iterator
+
+#include <array>
+
+#include <iterator>
+
+using iterator = std::array<int, 10>::iterator;
+using const_iterator = std::array<int, 10>::const_iterator;
+
+static_assert(std::indirectly_readable<iterator>);
+static_assert(std::indirectly_writable<iterator, int>);
+
+static_assert(std::indirectly_readable<const_iterator>);
+static_assert(!std::indirectly_writable<const_iterator, int>);

libcxx/test/std/containers/sequences/deque/iterator_concept_conformance.compile.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// iterator, const_iterator, reverse_iterator, const_reverse_iterator
+
+#include <deque>
+
+#include <iterator>
+
+using iterator = std::deque<int>::iterator;
+using const_iterator = std::deque<int>::const_iterator;
+using value_type = iterator::value_type;
+
+static_assert(std::indirectly_readable<iterator>);
+static_assert(std::indirectly_writable<iterator, value_type>);
+
+static_assert(std::indirectly_readable<const_iterator>);
+static_assert(!std::indirectly_writable<const_iterator, value_type>);

libcxx/test/std/containers/sequences/forwardlist/forwardlist.iter/iterator_concept_conformance.compile.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// iterator, const_iterator
+
+#include <forward_list>
+
+#include <iterator>
+
+using iterator = std::forward_list<int>::iterator;
+using const_iterator = std::forward_list<int>::const_iterator;
+using value_type = iterator::value_type;
+
+static_assert(std::indirectly_readable<iterator>);
+static_assert(std::indirectly_writable<iterator, value_type>);
+
+static_assert(std::indirectly_readable<const_iterator>);
+static_assert(!std::indirectly_writable<const_iterator, value_type>);

libcxx/test/std/containers/sequences/list/iterator_concept_conformance.compile.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// iterator, const_iterator, reverse_iterator, const_reverse_iterator
+
+#include <list>
+
+#include <iterator>
+
+using iterator = std::list<int>::iterator;
+using const_iterator = std::list<int>::const_iterator;
+using value_type = iterator::value_type;
+
+static_assert(std::indirectly_readable<iterator>);
+static_assert(std::indirectly_writable<iterator, value_type>);
+
+static_assert(std::indirectly_readable<const_iterator>);
+static_assert(!std::indirectly_writable<const_iterator, value_type>);

libcxx/test/std/containers/sequences/vector.bool/iterator_concept_conformance.compile.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// iterator, const_iterator, reverse_iterator, const_reverse_iterator
+
+#include <vector>
+
+#include <iterator>
+
+using iterator = std::vector<bool>::iterator;
+using const_iterator = std::vector<bool>::const_iterator;
+using value_type = iterator::value_type;
+
+static_assert(std::indirectly_readable<iterator>);
+static_assert(!std::indirectly_writable<iterator, value_type>);
+
+static_assert(std::indirectly_readable<const_iterator>);
+static_assert(!std::indirectly_writable<const_iterator, value_type>);