Revert "Revert "Implement common_iterator (#1092)" (#1265)"

stl/inc/xmemory

@@ -223,13 +223,6 @@ void _Deallocate(void* _Ptr, size_t _Bytes) noexcept {
 
 #undef _HAS_ALIGNED_NEW
 
-// FUNCTION TEMPLATE _Construct_in_place
-template <class _Ty, class... _Types>
-void _Construct_in_place(_Ty& _Obj, _Types&&... _Args) noexcept(is_nothrow_constructible_v<_Ty, _Types...>) {
-    ::new (const_cast<void*>(static_cast<const volatile void*>(_STD addressof(_Obj))))
-        _Ty(_STD forward<_Types>(_Args)...);
-}
-
 // FUNCTION TEMPLATE _Global_new
 template <class _Ty, class... _Types>
 _Ty* _Global_new(_Types&&... _Args) { // acts as "new" while disallowing user overload selection

stl/inc/xutility

@@ -119,6 +119,13 @@ struct _Get_rebind_alias<_Ty, _Other, void_t<typename _Ty::template rebind<_Othe
     using type = typename _Ty::template rebind<_Other>;
 };
 
+// FUNCTION TEMPLATE _Construct_in_place
+template <class _Ty, class... _Types>
+void _Construct_in_place(_Ty& _Obj, _Types&&... _Args) noexcept(is_nothrow_constructible_v<_Ty, _Types...>) {
+    ::new (const_cast<void*>(static_cast<const volatile void*>(_STD addressof(_Obj))))
+        _Ty(_STD forward<_Types>(_Args)...);
+}
+
 // STRUCT TEMPLATE pointer_traits
 template <class _Ty>
 struct pointer_traits {
@@ -2329,6 +2336,10 @@ _NODISCARD _Ty _Fake_decay_copy(_Ty) noexcept;
 // (2) is well-formed if and only if E is implicitly convertible to T and T is destructible, and
 // (3) is non-throwing if and only if both conversion from decltype((E)) to T and destruction of T are non-throwing.
 
+// CONCEPT _Not_same_as
+template <class _Ty1, class _Ty2>
+concept _Not_same_as = !same_as<remove_cvref_t<_Ty1>, remove_cvref_t<_Ty2>>;
+
 namespace ranges {
     // VARIABLE TEMPLATE _Has_complete_elements
     template <class>
@@ -3426,10 +3437,6 @@ namespace ranges {
         using is_transparent = int;
     };
 
-    // CONCEPT _Not_same_as
-    template <class _Ty1, class _Ty2>
-    concept _Not_same_as = !same_as<remove_cvref_t<_Ty1>, remove_cvref_t<_Ty2>>;
-
     // CONCEPT ranges::common_range
     // clang-format off
     template <class _Rng>

tests/std/include/range_algorithm_support.hpp

@@ -110,7 +110,16 @@ namespace test {
 
         using _Prevent_inheriting_unwrap = sentinel;
 
-        using unwrap = sentinel<Element, IsWrapped::no>;
+        using unwrap    = sentinel<Element, IsWrapped::no>;
+        using Constinel = sentinel<const Element, Wrapped>;
+
+        constexpr operator Constinel() && noexcept {
+            return Constinel{exchange(ptr_, nullptr)};
+        }
+
+        constexpr operator Constinel() const& noexcept {
+            return Constinel{ptr_};
+        }
 
         // clang-format off
         [[nodiscard]] constexpr auto _Unwrapped() const noexcept requires (to_bool(Wrapped)) {

tests/std/test.lst

@@ -242,6 +242,8 @@ tests\P0768R1_spaceship_operator
 tests\P0769R2_shift_left_shift_right
 tests\P0784R7_library_support_for_more_constexpr_containers
 tests\P0811R3_midpoint_lerp
+tests\P0896R4_common_iterator
+tests\P0896R4_common_iterator_death
 tests\P0896R4_counted_iterator
 tests\P0896R4_counted_iterator_death
 tests\P0896R4_P1614R2_comparisons

tests/std/tests/P0896R4_common_iterator/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\strict_concepts_matrix.lst

tests/std/tests/P0896R4_common_iterator/test.cpp

@@ -0,0 +1,201 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <concepts>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+
+#include <range_algorithm_support.hpp>
+using namespace std;
+using P = pair<int, int>;
+
+// clang-format off
+template <class Iter>
+concept CanDifference = requires(Iter it) {
+    { it - it };
+};
+
+template <class Iter>
+concept HasProxy = !is_reference_v<iter_reference_t<Iter>>;
+// clang-format on
+
+struct instantiator {
+    template <input_or_output_iterator Iter>
+    static constexpr void call() {
+        if constexpr (copyable<Iter>) {
+            using ConstIter = typename Iter::Consterator;
+            using Sen       = test::sentinel<iter_value_t<Iter>>;
+            using OSen      = test::sentinel<const iter_value_t<Iter>>;
+            using Cit       = common_iterator<Iter, Sen>;
+            using OCit      = common_iterator<ConstIter, OSen>;
+            P input[3]      = {{0, 1}, {0, 2}, {0, 3}};
+
+            // [common.iter.types]
+            {
+                using iconcept = typename iterator_traits<Cit>::iterator_concept;
+                if constexpr (forward_iterator<Iter>) {
+                    STATIC_ASSERT(same_as<iconcept, forward_iterator_tag>);
+                } else {
+                    STATIC_ASSERT(same_as<typename iterator_traits<Cit>::iterator_concept, input_iterator_tag>);
+                }
+
+                using icat = typename iterator_traits<Cit>::iterator_category;
+                if constexpr (derived_from<icat, forward_iterator_tag>) {
+                    STATIC_ASSERT(same_as<icat, forward_iterator_tag>);
+                } else {
+                    STATIC_ASSERT(same_as<icat, input_iterator_tag>);
+                }
+
+                using ipointer = typename iterator_traits<Cit>::pointer;
+                if constexpr (_Has_member_arrow<Iter>) {
+                    STATIC_ASSERT(same_as<ipointer, decltype(declval<const Iter&>().operator->())>);
+                } else {
+                    STATIC_ASSERT(same_as<ipointer, void>);
+                }
+            }
+
+            { // [common.iter.const]
+                Cit defaultConstructed{};
+                Cit iterConstructed{Iter{input}};
+                Cit sentinelConstructed(Sen{});
+                Cit copyConstructed{defaultConstructed};
+                copyConstructed = iterConstructed;
+
+                OCit conversionConstructed{defaultConstructed};
+                conversionConstructed = iterConstructed;
+
+                OCit conversionConstructedSentinel{sentinelConstructed};
+                conversionConstructed = iterConstructed;
+            }
+
+            { // [common.iter.access]
+                Cit iter{Iter{input}};
+                assert(*iter == P(0, 1));
+                assert(iter->first == 0);
+                assert(iter->second == 1);
+                if constexpr (HasProxy<Iter>) {
+                    // We return a proxy class here
+                    static_assert(is_class_v<decltype(iter.operator->())>);
+                } else {
+                    // Either a pointer or the wrapped iterator
+                    static_assert(!is_class_v<decltype(iter.operator->())>);
+                }
+
+                const Cit constIter{Iter{input}};
+                assert(*constIter == P(0, 1));
+                assert(constIter->first == 0);
+                assert(constIter->second == 1);
+                if constexpr (HasProxy<Iter>) {
+                    // We return a proxy class here
+                    static_assert(is_class_v<decltype(constIter.operator->())>);
+                } else {
+                    // Either a pointer or the wrapped iterator
+                    static_assert(!is_class_v<decltype(constIter.operator->())>);
+                }
+            }
+
+            { // [common.iter.nav]
+                Cit iter{Iter{input}};
+                ++iter;
+                assert(*iter == P(0, 2));
+
+                assert(*iter++ == P(0, 2));
+                assert(*iter == P(0, 3));
+            }
+
+            { // [common.iter.cmp]
+                // Compare iterator / iterator
+                assert(Cit{Iter{input}} == Cit{Iter{input}});
+                assert(Cit{Iter{input}} != Cit{Iter{input + 1}});
+
+                // Compare iterator / sentinel
+                assert(Cit{Iter{input}} == Cit{Sen{input}});
+                assert(Cit{Sen{input}} != Cit{Iter{input + 1}});
+
+                // Compare sentinel / sentinel
+                assert(Cit{Sen{input}} == Cit{Sen{input}});
+                assert(Cit{Sen{input}} == Cit{Sen{input + 1}});
+
+                if constexpr (CanDifference<Iter>) {
+                    // Difference iterator / iterator
+                    const same_as<iter_difference_t<Iter>> auto diff_it_it = Cit{Iter{input}} - Cit{Iter{input + 1}};
+                    assert(diff_it_it == -1);
+
+                    // Difference iterator / sentinel
+                    const same_as<iter_difference_t<Iter>> auto diff_it_sen = Cit{Iter{input}} - Cit{Sen{input + 1}};
+                    const same_as<iter_difference_t<Iter>> auto diff_sen_it = Cit{Sen{input + 1}} - Cit{Iter{input}};
+                    assert(diff_it_sen == -1);
+                    assert(diff_sen_it == 1);
+
+                    // Difference sentinel / sentinel
+                    const same_as<iter_difference_t<Iter>> auto diff_sen_sen = Cit{Sen{input}} - Cit{Sen{input + 1}};
+                    assert(diff_sen_sen == 0);
+
+                    // Difference iterator / other iterator
+                    const same_as<iter_difference_t<Iter>> auto diff_it_oit = Cit{Iter{input}} - OCit{Iter{input + 1}};
+                    assert(diff_it_oit == -1);
+
+                    // Difference iterator / other sentinel
+                    const same_as<iter_difference_t<Iter>> auto diff_it_osen = Cit{Iter{input}} - OCit{OSen{input + 1}};
+                    assert(diff_it_osen == -1);
+
+                    // Difference other iterator / sentinel
+                    const same_as<iter_difference_t<Iter>> auto diff_sen_oit = Cit{Sen{input + 1}} - OCit{Iter{input}};
+                    assert(diff_sen_oit == 1);
+
+                    // Difference sentinel / other sentinel
+                    const same_as<iter_difference_t<Iter>> auto diff_sen_osen = Cit{Sen{input}} - OCit{OSen{input + 1}};
+                    assert(diff_sen_osen == 0);
+                }
+            }
+
+            { // [common.iter.cust]
+                if constexpr (input_iterator<Iter>) { // iter_move
+                    Cit iter1{Iter{input}};
+
+                    const same_as<iter_value_t<Iter>> auto element1 = ranges::iter_move(iter1);
+                    assert(element1 == P(0, 1));
+                }
+
+                if constexpr (indirectly_swappable<Iter>) { // iter_swap
+                    Cit iter1{Iter{input}};
+                    Cit iter2{Iter{input + 1}};
+
+                    ranges::iter_swap(iter1, iter2);
+                    assert(*iter1 == P(0, 2));
+                    assert(*iter2 == P(0, 1));
+                }
+            }
+        }
+    }
+};
+
+bool test_operator_arrow() {
+    P input[3] = {{0, 1}, {0, 2}, {0, 3}};
+
+    using pointerTest = common_iterator<P*, void*>;
+    pointerTest pointerIter{input};
+
+    assert(*pointerIter == P(0, 1));
+    assert(pointerIter->first == 0);
+    assert(pointerIter->second == 1);
+    static_assert(is_same_v<decltype(pointerIter.operator->()), P* const&>);
+
+    using countedTest = common_iterator<counted_iterator<P*>, default_sentinel_t>;
+    countedTest countedIter{counted_iterator{input, 3}};
+
+    assert(*countedIter == P(0, 1));
+    assert(countedIter->first == 0);
+    assert(countedIter->second == 1);
+    static_assert(is_same_v<decltype(countedIter.operator->()), P*>);
+
+    return true;
+}
+
+int main() {
+    with_writable_iterators<instantiator, P>::call();
+
+    test_operator_arrow();
+}

tests/std/tests/P0896R4_common_iterator_death/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\strict_winsdk_concepts_matrix.lst