Implement ranges::remove family (#1005)

stl/inc/algorithm

@@ -386,6 +386,21 @@ namespace ranges {
     inline constexpr _For_each_n_fn for_each_n{_Not_quite_object::_Construct_tag{}};
 
     // VARIABLE ranges::find
+    // clang-format off
+    // concept-constrained for strict enforcement as it is used by several algorithms
+    template <input_iterator _It, sentinel_for<_It> _Se, class _Ty, class _Pj>
+        requires indirect_binary_predicate<ranges::equal_to, projected<_It, _Pj>, const _Ty*>
+    _NODISCARD constexpr _It _Find_unchecked(_It _First, const _Se _Last, const _Ty& _Val, _Pj _Proj) {
+        for (; _First != _Last; ++_First) {
+            if (_STD invoke(_Proj, *_First) == _Val) {
+                break;
+            }
+        }
+
+        return _First;
+    }
+    // clang-format on
+
     class _Find_fn : private _Not_quite_object {
     public:
         using _Not_quite_object::_Not_quite_object;
@@ -395,16 +410,10 @@ namespace ranges {
             requires indirect_binary_predicate<ranges::equal_to, projected<_It, _Pj>, const _Ty*>
         _NODISCARD constexpr _It operator()(_It _First, _Se _Last, const _Ty& _Val, _Pj _Proj = {}) const {
             _Adl_verify_range(_First, _Last);
-            // Performance note: investigate using _Find_unchecked when same_as<_Pj, identity>
-            auto _UFirst      = _Get_unwrapped(_STD move(_First));
-            const auto _ULast = _Get_unwrapped(_STD move(_Last));
-            for (; _UFirst != _ULast; ++_UFirst) {
-                if (_STD invoke(_Proj, *_UFirst) == _Val) {
-                    break;
-                }
-            }
+            auto _UResult = _RANGES _Find_unchecked(
+                _Get_unwrapped(_STD move(_First)), _Get_unwrapped(_STD move(_Last)), _Val, _Pass_fn(_Proj));
 
-            _Seek_wrapped(_First, _STD move(_UFirst));
+            _Seek_wrapped(_First, _STD move(_UResult));
             return _First;
         }
 
@@ -412,7 +421,12 @@ namespace ranges {
             requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Rng>, _Pj>, const _Ty*>
         _NODISCARD constexpr borrowed_iterator_t<_Rng> operator()(
             _Rng&& _Range, const _Ty& _Val, _Pj _Proj = {}) const {
-            return (*this)(_RANGES begin(_Range), _RANGES end(_Range), _Val, _Pass_fn(_Proj));
+            auto _First = _RANGES begin(_Range);
+            auto _UResult =
+                _RANGES _Find_unchecked(_Get_unwrapped(_STD move(_First)), _Uend(_Range), _Val, _Pass_fn(_Proj));
+
+            _Seek_wrapped(_First, _STD move(_UResult));
+            return _First;
         }
         // clang-format on
     };
@@ -430,6 +444,18 @@ _NODISCARD _FwdIt find_if(_ExPo&& _Exec, _FwdIt _First, const _FwdIt _Last, _Pr
 #ifdef __cpp_lib_concepts
 namespace ranges {
     // VARIABLE ranges::find_if
+    // concept-constrained for strict enforcement as it is used by several algorithms
+    template <input_iterator _It, sentinel_for<_It> _Se, class _Pj, indirect_unary_predicate<projected<_It, _Pj>> _Pr>
+    _NODISCARD constexpr _It _Find_if_unchecked(_It _First, const _Se _Last, _Pr _Pred, _Pj _Proj) {
+        for (; _First != _Last; ++_First) {
+            if (_STD invoke(_Pred, _STD invoke(_Proj, *_First))) {
+                break;
+            }
+        }
+
+        return _First;
+    }
+
     class _Find_if_fn : private _Not_quite_object {
     public:
         using _Not_quite_object::_Not_quite_object;
@@ -438,22 +464,22 @@ namespace ranges {
             indirect_unary_predicate<projected<_It, _Pj>> _Pr>
         _NODISCARD constexpr _It operator()(_It _First, _Se _Last, _Pr _Pred, _Pj _Proj = {}) const {
             _Adl_verify_range(_First, _Last);
-            auto _UFirst      = _Get_unwrapped(_STD move(_First));
-            const auto _ULast = _Get_unwrapped(_STD move(_Last));
-            for (; _UFirst != _ULast; ++_UFirst) {
-                if (_STD invoke(_Pred, _STD invoke(_Proj, *_UFirst))) {
-                    break;
-                }
-            }
+            auto _UResult = _RANGES _Find_if_unchecked(
+                _Get_unwrapped(_STD move(_First)), _Get_unwrapped(_STD move(_Last)), _Pass_fn(_Pred), _Pass_fn(_Proj));
 
-            _Seek_wrapped(_First, _STD move(_UFirst));
+            _Seek_wrapped(_First, _STD move(_UResult));
             return _First;
         }
 
         template <input_range _Rng, class _Pj = identity,
             indirect_unary_predicate<projected<iterator_t<_Rng>, _Pj>> _Pr>
         _NODISCARD constexpr borrowed_iterator_t<_Rng> operator()(_Rng&& _Range, _Pr _Pred, _Pj _Proj = {}) const {
-            return (*this)(_RANGES begin(_Range), _RANGES end(_Range), _Pass_fn(_Pred), _Pass_fn(_Proj));
+            auto _First   = _RANGES begin(_Range);
+            auto _UResult = _RANGES _Find_if_unchecked(
+                _Get_unwrapped(_STD move(_First)), _Uend(_Range), _Pass_fn(_Pred), _Pass_fn(_Proj));
+
+            _Seek_wrapped(_First, _STD move(_UResult));
+            return _First;
         }
     };
 
@@ -3985,13 +4011,247 @@ _FwdIt2 remove_copy_if(_ExPo&&, _FwdIt1 _First, _FwdIt1 _Last, _FwdIt2 _Dest, _P
 template <class _ExPo, class _FwdIt, class _Ty, _Enable_if_execution_policy_t<_ExPo> = 0>
 _NODISCARD _FwdIt remove(
     _ExPo&& _Exec, const _FwdIt _First, const _FwdIt _Last, const _Ty& _Val) noexcept; // terminates
-#endif // _HAS_CXX17
 
-#if _HAS_CXX17
 template <class _ExPo, class _FwdIt, class _Pr, _Enable_if_execution_policy_t<_ExPo> = 0>
 _NODISCARD _FwdIt remove_if(_ExPo&& _Exec, _FwdIt _First, const _FwdIt _Last, _Pr _Pred) noexcept; // terminates
 #endif // _HAS_CXX17
 
+#ifdef __cpp_lib_concepts
+namespace ranges {
+    // VARIABLE ranges::remove
+    class _Remove_fn : private _Not_quite_object {
+    public:
+        using _Not_quite_object::_Not_quite_object;
+
+        // clang-format off
+        template <permutable _It, sentinel_for<_It> _Se, class _Ty, class _Pj = identity>
+            requires indirect_binary_predicate<ranges::equal_to, projected<_It, _Pj>, const _Ty*>
+        _NODISCARD constexpr subrange<_It> operator()(_It _First, _Se _Last, const _Ty& _Val, _Pj _Proj = {}) const {
+            _Adl_verify_range(_First, _Last);
+            auto _UResult = _Remove_unchecked(
+                _Get_unwrapped(_STD move(_First)), _Get_unwrapped(_STD move(_Last)), _Val, _Pass_fn(_Proj));
+
+            return _Rewrap_subrange<subrange<_It>>(_First, _STD move(_UResult));
+        }
+
+        template <forward_range _Rng, class _Ty, class _Pj = identity>
+            requires permutable<iterator_t<_Rng>>
+                  && indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Rng>, _Pj>, const _Ty*>
+        _NODISCARD constexpr borrowed_subrange_t<_Rng> operator()(
+            _Rng&& _Range, const _Ty& _Val, _Pj _Proj = {}) const {
+            auto _UResult = _Remove_unchecked(_Ubegin(_Range), _Uend(_Range), _Val, _Pass_fn(_Proj));
+
+            return _Rewrap_subrange<borrowed_subrange_t<_Rng>>(_Range, _STD move(_UResult));
+        }
+        // clang-format on
+    private:
+        template <class _It, class _Se, class _Ty, class _Pj>
+        _NODISCARD static constexpr subrange<_It> _Remove_unchecked(
+            _It _First, const _Se _Last, const _Ty& _Val, _Pj _Proj) {
+            // Remove projected values equal to _Val from [_First, _Last)
+            _STL_INTERNAL_STATIC_ASSERT(permutable<_It>);
+            _STL_INTERNAL_STATIC_ASSERT(sentinel_for<_Se, _It>);
+            _STL_INTERNAL_STATIC_ASSERT(indirect_binary_predicate<ranges::equal_to, projected<_It, _Pj>, const _Ty*>);
+
+            _First     = _RANGES _Find_unchecked(_STD move(_First), _Last, _Val, _Proj);
+            auto _Next = _First;
+            if (_First == _Last) {
+                return {_STD move(_Next), _STD move(_First)};
+            }
+
+            while (++_First != _Last) {
+                if (_STD invoke(_Proj, *_First) != _Val) {
+                    *_Next = _RANGES iter_move(_First);
+                    ++_Next;
+                }
+            }
+
+            return {_STD move(_Next), _STD move(_First)};
+        }
+    };
+
+    inline constexpr _Remove_fn remove{_Not_quite_object::_Construct_tag{}};
+
+    // VARIABLE ranges::remove_if
+    class _Remove_if_fn : private _Not_quite_object {
+    public:
+        using _Not_quite_object::_Not_quite_object;
+
+        template <permutable _It, sentinel_for<_It> _Se, class _Pj = identity,
+            indirect_unary_predicate<projected<_It, _Pj>> _Pr>
+        _NODISCARD constexpr subrange<_It> operator()(_It _First, _Se _Last, _Pr _Pred, _Pj _Proj = {}) const {
+            _Adl_verify_range(_First, _Last);
+            auto _UResult = _Remove_if_unchecked(
+                _Get_unwrapped(_STD move(_First)), _Get_unwrapped(_STD move(_Last)), _Pass_fn(_Pred), _Pass_fn(_Proj));
+
+            return _Rewrap_subrange<subrange<_It>>(_First, _STD move(_UResult));
+        }
+
+        // clang-format off
+        template <forward_range _Rng, class _Pj = identity,
+            indirect_unary_predicate<projected<iterator_t<_Rng>, _Pj>> _Pr>
+            requires permutable<iterator_t<_Rng>>
+        _NODISCARD constexpr borrowed_subrange_t<_Rng> operator()(_Rng&& _Range, _Pr _Pred, _Pj _Proj = {}) const {
+            auto _UResult = _Remove_if_unchecked(_Ubegin(_Range), _Uend(_Range), _Pass_fn(_Pred), _Pass_fn(_Proj));
+
+            return _Rewrap_subrange<borrowed_subrange_t<_Rng>>(_Range, _STD move(_UResult));
+        }
+        // clang-format on
+    private:
+        template <class _It, class _Se, class _Pr, class _Pj>
+        _NODISCARD static constexpr subrange<_It> _Remove_if_unchecked(
+            _It _First, const _Se _Last, _Pr _Pred, _Pj _Proj) {
+            // Remove values whose projection satisfies _Pred from [_First, _Last)
+            _STL_INTERNAL_STATIC_ASSERT(permutable<_It>);
+            _STL_INTERNAL_STATIC_ASSERT(sentinel_for<_Se, _It>);
+            _STL_INTERNAL_STATIC_ASSERT(indirect_unary_predicate<_Pr, projected<_It, _Pj>>);
+
+            _First     = _RANGES _Find_if_unchecked(_STD move(_First), _Last, _Pred, _Proj);
+            auto _Next = _First;
+            if (_First == _Last) {
+                return {_STD move(_Next), _STD move(_First)};
+            }
+
+            while (++_First != _Last) {
+                if (!_STD invoke(_Pred, _STD invoke(_Proj, *_First))) {
+                    *_Next = _RANGES iter_move(_First);
+                    ++_Next;
+                }
+            }
+
+            return {_STD move(_Next), _STD move(_First)};
+        }
+    };
+
+    inline constexpr _Remove_if_fn remove_if{_Not_quite_object::_Construct_tag{}};
+
+    // ALIAS TEMPLATE remove_copy_result
+    template <class _In, class _Out>
+    using remove_copy_result = in_out_result<_In, _Out>;
+
+    // VARIABLE ranges::remove_copy
+    class _Remove_copy_fn : private _Not_quite_object {
+    public:
+        using _Not_quite_object::_Not_quite_object;
+
+        // clang-format off
+        template <input_iterator _It, sentinel_for<_It> _Se, weakly_incrementable _Out, class _Ty, class _Pj = identity>
+            requires indirectly_copyable<_It, _Out>
+                  && indirect_binary_predicate<ranges::equal_to, projected<_It, _Pj>, const _Ty*>
+        constexpr remove_copy_result<_It, _Out> operator()(
+            _It _First, _Se _Last, _Out _Result, const _Ty& _Val, _Pj _Proj = {}) const {
+            _Adl_verify_range(_First, _Last);
+            auto _UResult = _Remove_copy_unchecked(_Get_unwrapped(_STD move(_First)), _Get_unwrapped(_STD move(_Last)),
+                _Get_unwrapped_unverified(_STD move(_Result)), _Val, _Pass_fn(_Proj));
+
+            _Seek_wrapped(_First, _STD move(_UResult.in));
+            _Seek_wrapped(_Result, _STD move(_UResult.out));
+            return {_STD move(_First), _STD move(_Result)};
+        }
+
+        template <input_range _Rng, weakly_incrementable _Out, class _Ty, class _Pj = identity>
+            requires indirectly_copyable<iterator_t<_Rng>, _Out>
+                  && indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Rng>, _Pj>, const _Ty*>
+        constexpr remove_copy_result<borrowed_iterator_t<_Rng>, _Out> operator()(
+            _Rng&& _Range, _Out _Result, const _Ty& _Val, _Pj _Proj = {}) const {
+            auto _First   = _RANGES begin(_Range);
+            auto _UResult = _Remove_copy_unchecked(_Get_unwrapped(_STD move(_First)), _Uend(_Range),
+                _Get_unwrapped_unverified(_STD move(_Result)), _Val, _Pass_fn(_Proj));
+
+            _Seek_wrapped(_First, _STD move(_UResult.in));
+            _Seek_wrapped(_Result, _STD move(_UResult.out));
+            return {_STD move(_First), _STD move(_Result)};
+        }
+        // clang-format on
+    private:
+        template <class _It, class _Se, class _Out, class _Ty, class _Pj>
+        _NODISCARD static constexpr remove_copy_result<_It, _Out> _Remove_copy_unchecked(
+            _It _First, const _Se _Last, _Out _Result, const _Ty& _Val, _Pj _Proj) {
+            // Copy [_First, _Last) to _Result except projected values equal to _Val
+            _STL_INTERNAL_STATIC_ASSERT(input_iterator<_It>);
+            _STL_INTERNAL_STATIC_ASSERT(sentinel_for<_Se, _It>);
+            _STL_INTERNAL_STATIC_ASSERT(weakly_incrementable<_Out>);
+            _STL_INTERNAL_STATIC_ASSERT(indirectly_copyable<_It, _Out>);
+            _STL_INTERNAL_STATIC_ASSERT(indirect_binary_predicate<ranges::equal_to, projected<_It, _Pj>, const _Ty*>);
+
+            for (; _First != _Last; ++_First) {
+                if (_STD invoke(_Proj, *_First) != _Val) {
+                    *_Result = *_First;
+                    ++_Result;
+                }
+            }
+
+            return {_STD move(_First), _STD move(_Result)};
+        }
+    };
+
+    inline constexpr _Remove_copy_fn remove_copy{_Not_quite_object::_Construct_tag{}};
+
+    // ALIAS TEMPLATE remove_copy_if_result
+    template <class _In, class _Out>
+    using remove_copy_if_result = in_out_result<_In, _Out>;
+
+    // VARIABLE ranges::remove_copy_if
+    class _Remove_copy_if_fn : private _Not_quite_object {
+    public:
+        using _Not_quite_object::_Not_quite_object;
+
+        // clang-format off
+        template <input_iterator _It, sentinel_for<_It> _Se, weakly_incrementable _Out, class _Pj = identity,
+            indirect_unary_predicate<projected<_It, _Pj>> _Pr>
+            requires indirectly_copyable<_It, _Out>
+        constexpr remove_copy_if_result<_It, _Out> operator()(
+            _It _First, _Se _Last, _Out _Result, _Pr _Pred, _Pj _Proj = {}) const {
+            _Adl_verify_range(_First, _Last);
+            auto _UResult =
+                _Remove_copy_if_unchecked(_Get_unwrapped(_STD move(_First)), _Get_unwrapped(_STD move(_Last)),
+                    _Get_unwrapped_unverified(_STD move(_Result)), _Pass_fn(_Pred), _Pass_fn(_Proj));
+
+            _Seek_wrapped(_First, _STD move(_UResult.in));
+            _Seek_wrapped(_Result, _STD move(_UResult.out));
+            return {_STD move(_First), _STD move(_Result)};
+        }
+
+        template <input_range _Rng, weakly_incrementable _Out, class _Pj = identity,
+            indirect_unary_predicate<projected<iterator_t<_Rng>, _Pj>> _Pr>
+            requires indirectly_copyable<iterator_t<_Rng>, _Out>
+        constexpr remove_copy_if_result<borrowed_iterator_t<_Rng>, _Out> operator()(
+            _Rng&& _Range, _Out _Result, _Pr _Pred, _Pj _Proj = {}) const {
+            auto _First   = _RANGES begin(_Range);
+            auto _UResult = _Remove_copy_if_unchecked(_Get_unwrapped(_STD move(_First)), _Uend(_Range),
+                _Get_unwrapped_unverified(_STD move(_Result)), _Pass_fn(_Pred), _Pass_fn(_Proj));
+
+            _Seek_wrapped(_First, _STD move(_UResult.in));
+            _Seek_wrapped(_Result, _STD move(_UResult.out));
+            return {_STD move(_First), _STD move(_Result)};
+        }
+        // clang-format on
+    private:
+        template <class _It, class _Se, class _Out, class _Pr, class _Pj>
+        _NODISCARD static constexpr remove_copy_if_result<_It, _Out> _Remove_copy_if_unchecked(
+            _It _First, const _Se _Last, _Out _Result, _Pr _Pred, _Pj _Proj) {
+            // Copy [_First, _Last) to _Result except projected values that satisfy _Pred
+            _STL_INTERNAL_STATIC_ASSERT(input_iterator<_It>);
+            _STL_INTERNAL_STATIC_ASSERT(sentinel_for<_Se, _It>);
+            _STL_INTERNAL_STATIC_ASSERT(weakly_incrementable<_Out>);
+            _STL_INTERNAL_STATIC_ASSERT(indirectly_copyable<_It, _Out>);
+            _STL_INTERNAL_STATIC_ASSERT(indirect_unary_predicate<_Pr, projected<_It, _Pj>>);
+
+            for (; _First != _Last; ++_First) {
+                if (!_STD invoke(_Pred, _STD invoke(_Proj, *_First))) {
+                    *_Result = *_First;
+                    ++_Result;
+                }
+            }
+
+            return {_STD move(_First), _STD move(_Result)};
+        }
+    };
+
+    inline constexpr _Remove_copy_if_fn remove_copy_if{_Not_quite_object::_Construct_tag{}};
+} // namespace ranges
+#endif // __cpp_lib_concepts
+
 // FUNCTION TEMPLATE unique
 template <class _FwdIt, class _Pr>
 _NODISCARD _CONSTEXPR20 _FwdIt unique(_FwdIt _First, _FwdIt _Last, _Pr _Pred) {

tests/std/include/range_algorithm_support.hpp

@@ -1008,6 +1008,11 @@ constexpr void test_in_write() {
     with_input_ranges<with_writable_iterators<Instantiator, Element2>, Element1>::call();
 }
 
+template <class Instantiator, class Element1, class Element2>
+constexpr void test_fwd_write() {
+    with_forward_ranges<with_writable_iterators<Instantiator, Element2>, Element1>::call();
+}
+
 template <class Instantiator, class Element>
 constexpr void test_read() {
     with_input_iterators<Instantiator, Element>::call();

tests/std/test.lst

@@ -266,6 +266,10 @@ tests\P0896R4_ranges_alg_none_of
 tests\P0896R4_ranges_alg_partition
 tests\P0896R4_ranges_alg_partition_copy
 tests\P0896R4_ranges_alg_partition_point
+tests\P0896R4_ranges_alg_remove
+tests\P0896R4_ranges_alg_remove_copy
+tests\P0896R4_ranges_alg_remove_copy_if
+tests\P0896R4_ranges_alg_remove_if
 tests\P0896R4_ranges_alg_replace
 tests\P0896R4_ranges_alg_replace_copy
 tests\P0896R4_ranges_alg_replace_copy_if

tests/std/tests/P0896R4_ranges_alg_remove/env.lst

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

tests/std/tests/P0896R4_ranges_alg_remove/test.cpp

@@ -0,0 +1,69 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <algorithm>
+#include <cassert>
+#include <concepts>
+#include <ranges>
+#include <span>
+#include <utility>
+
+#include <range_algorithm_support.hpp>
+using namespace std;
+using P = pair<int, int>;
+
+// Validate dangling story
+STATIC_ASSERT(same_as<decltype(ranges::remove(borrowed<false>{}, 42)), ranges::dangling>);
+STATIC_ASSERT(same_as<decltype(ranges::remove(borrowed<true>{}, 42)), ranges::subrange<int*>>);
+
+struct instantiator {
+    static constexpr P expected[3] = {{0, 99}, {2, 99}, {4, 99}};
+
+    template <ranges::forward_range Read>
+    static constexpr void call() {
+#if !defined(__clang__) && !defined(__EDG__) // TRANSITION, VSO-938163
+#pragma warning(suppress : 4127) // conditional expression is constant
+        if (!ranges::contiguous_range<Read> || !is_constant_evaluated())
+#endif // TRANSITION, VSO-938163
+        {
+            using ranges::remove, ranges::subrange, ranges::equal, ranges::iterator_t;
+
+            size_t projectionCounter = 0;
+            auto projection          = [&projectionCounter](const P& val) {
+                ++projectionCounter;
+                return val.second;
+            };
+
+            { // Validate iterator + sentinel overload
+                P input[5] = {{0, 99}, {1, 47}, {2, 99}, {3, 47}, {4, 99}};
+                Read wrapped_input{input};
+
+                auto result = remove(wrapped_input.begin(), wrapped_input.end(), 47, projection);
+                STATIC_ASSERT(same_as<decltype(result), subrange<iterator_t<Read>>>);
+                assert(result.begin() == next(wrapped_input.begin(), 3));
+                assert(result.end() == wrapped_input.end());
+                assert(equal(expected, span{input}.first<3>()));
+                assert(projectionCounter == ranges::size(input));
+            }
+
+            projectionCounter = 0;
+
+            { // Validate range overload
+                P input[5] = {{0, 99}, {1, 47}, {2, 99}, {3, 47}, {4, 99}};
+                Read wrapped_input{input};
+
+                auto result = remove(wrapped_input, 47, projection);
+                STATIC_ASSERT(same_as<decltype(result), subrange<iterator_t<Read>>>);
+                assert(result.begin() == next(wrapped_input.begin(), 3));
+                assert(result.end() == wrapped_input.end());
+                assert(equal(expected, span{input}.first<3>()));
+                assert(projectionCounter == ranges::size(input));
+            }
+        }
+    }
+};
+
+int main() {
+    STATIC_ASSERT((test_fwd<instantiator, P>(), true));
+    test_fwd<instantiator, P>();
+}

tests/std/tests/P0896R4_ranges_alg_remove_copy/env.lst

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

tests/std/tests/P0896R4_ranges_alg_remove_copy/test.cpp

@@ -0,0 +1,76 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <algorithm>
+#include <cassert>
+#include <concepts>
+#include <ranges>
+#include <utility>
+
+#include <range_algorithm_support.hpp>
+using namespace std;
+using P = pair<int, int>;
+
+// Validate that remove_copy_result aliases in_out_result
+STATIC_ASSERT(same_as<ranges::remove_copy_result<int, double>, ranges::in_out_result<int, double>>);
+
+// Validate dangling story
+STATIC_ASSERT(same_as<decltype(ranges::remove_copy(borrowed<false>{}, static_cast<int*>(nullptr), 42)),
+    ranges::remove_copy_result<ranges::dangling, int*>>);
+STATIC_ASSERT(same_as<decltype(ranges::remove_copy(borrowed<true>{}, static_cast<int*>(nullptr), 42)),
+    ranges::remove_copy_result<int*, int*>>);
+
+struct instantiator {
+    static constexpr P input[5]    = {{0, 99}, {1, 47}, {2, 99}, {3, 47}, {4, 99}};
+    static constexpr P expected[3] = {{0, 99}, {2, 99}, {4, 99}};
+
+    template <ranges::input_range Read, indirectly_writable<ranges::range_reference_t<Read>> Write>
+    static constexpr void call() {
+        // Fails checking the indirect_binary_predicate requirement in C1XX's permissive mode with proxy iterators
+        // (probably related to VSO-566808)
+        constexpr bool non_proxy =
+            is_reference_v<ranges::range_reference_t<Read>> && is_reference_v<iter_reference_t<Write>>;
+        if constexpr (non_proxy || !is_permissive) {
+            using ranges::remove_copy, ranges::remove_copy_result, ranges::equal, ranges::iterator_t;
+
+            size_t projectionCounter = 0;
+            auto projection          = [&projectionCounter](const P& val) {
+                ++projectionCounter;
+                return val.second;
+            };
+
+            { // Validate iterator + sentinel overload
+                P output[3] = {{-1, -1}, {-1, -1}, {-1, -1}};
+                Read wrapped_input{input};
+
+                auto result = remove_copy(wrapped_input.begin(), wrapped_input.end(), Write{output}, 47, projection);
+                STATIC_ASSERT(same_as<decltype(result), remove_copy_result<iterator_t<Read>, Write>>);
+                assert(result.in == wrapped_input.end());
+                assert(result.out.peek() == output + 3);
+                assert(equal(output, expected));
+                assert(projectionCounter == ranges::size(input));
+            }
+
+            projectionCounter = 0;
+
+            { // Validate range overload
+                P output[3] = {{-1, -1}, {-1, -1}, {-1, -1}};
+                Read wrapped_input{input};
+
+                auto result = remove_copy(wrapped_input, Write{output}, 47, projection);
+                STATIC_ASSERT(same_as<decltype(result), remove_copy_result<iterator_t<Read>, Write>>);
+                assert(result.in == wrapped_input.end());
+                assert(result.out.peek() == output + 3);
+                assert(equal(output, expected));
+                assert(projectionCounter == ranges::size(input));
+            }
+        }
+    }
+};
+
+int main() {
+#ifndef _PREFAST_ // TRANSITION, GH-1030
+    STATIC_ASSERT((test_in_write<instantiator, const P, P>(), true));
+#endif // TRANSITION, GH-1030
+    test_in_write<instantiator, const P, P>();
+}

tests/std/tests/P0896R4_ranges_alg_remove_copy_if/env.lst

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

tests/std/tests/P0896R4_ranges_alg_remove_copy_if/test.cpp

@@ -0,0 +1,77 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <algorithm>
+#include <cassert>
+#include <concepts>
+#include <ranges>
+#include <utility>
+
+#include <range_algorithm_support.hpp>
+using namespace std;
+using P = pair<int, int>;
+
+constexpr auto matches = [](const int val) { return val == 47; };
+
+// Validate that remove_copy_if_result aliases in_out_result
+STATIC_ASSERT(same_as<ranges::remove_copy_if_result<int, double>, ranges::in_out_result<int, double>>);
+
+// Validate dangling story
+STATIC_ASSERT(same_as<decltype(ranges::remove_copy_if(borrowed<false>{}, static_cast<int*>(nullptr), matches)),
+    ranges::remove_copy_if_result<ranges::dangling, int*>>);
+STATIC_ASSERT(same_as<decltype(ranges::remove_copy_if(borrowed<true>{}, static_cast<int*>(nullptr), matches)),
+    ranges::remove_copy_if_result<int*, int*>>);
+
+struct instantiator {
+    static constexpr P input[5]    = {{0, 99}, {1, 47}, {2, 99}, {3, 47}, {4, 99}};
+    static constexpr P expected[3] = {{0, 99}, {2, 99}, {4, 99}};
+
+    template <ranges::input_range Read, indirectly_writable<ranges::range_reference_t<Read>> Write>
+    static constexpr void call() {
+        // Fails checking the indirect_binary_predicate requirement in C1XX's permissive mode with proxy iterators
+        // (probably related to VSO-566808)
+        constexpr bool non_proxy =
+            is_reference_v<ranges::range_reference_t<Read>> && is_reference_v<iter_reference_t<Write>>;
+        if constexpr (non_proxy || !is_permissive) {
+            using ranges::remove_copy_if, ranges::remove_copy_if_result, ranges::equal, ranges::iterator_t;
+
+            size_t projectionCounter = 0;
+            auto projection          = [&projectionCounter](const P& val) {
+                ++projectionCounter;
+                return val.second;
+            };
+
+            { // Validate iterator + sentinel overload
+                P output[3] = {{-1, -1}, {-1, -1}, {-1, -1}};
+                Read wrapped_input{input};
+                auto result =
+                    remove_copy_if(wrapped_input.begin(), wrapped_input.end(), Write{output}, matches, projection);
+                STATIC_ASSERT(same_as<decltype(result), remove_copy_if_result<iterator_t<Read>, Write>>);
+                assert(result.in == wrapped_input.end());
+                assert(result.out.peek() == output + 3);
+                assert(equal(output, expected));
+                assert(projectionCounter == ranges::size(input));
+            }
+
+            projectionCounter = 0;
+
+            { // Validate range overload
+                P output[3] = {{-1, -1}, {-1, -1}, {-1, -1}};
+                Read wrapped_input{input};
+                auto result = remove_copy_if(wrapped_input, Write{output}, matches, projection);
+                STATIC_ASSERT(same_as<decltype(result), remove_copy_if_result<iterator_t<Read>, Write>>);
+                assert(result.in == wrapped_input.end());
+                assert(result.out.peek() == output + 3);
+                assert(equal(output, expected));
+                assert(projectionCounter == ranges::size(input));
+            }
+        }
+    }
+};
+
+int main() {
+#ifndef _PREFAST_ // TRANSITION, GH-1030
+    STATIC_ASSERT((test_in_write<instantiator, const P, P>(), true));
+#endif // TRANSITION, GH-1030
+    test_in_write<instantiator, const P, P>();
+}

tests/std/tests/P0896R4_ranges_alg_remove_if/env.lst

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

tests/std/tests/P0896R4_ranges_alg_remove_if/test.cpp

@@ -0,0 +1,71 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <algorithm>
+#include <cassert>
+#include <concepts>
+#include <ranges>
+#include <span>
+#include <utility>
+
+#include <range_algorithm_support.hpp>
+using namespace std;
+using P = pair<int, int>;
+
+constexpr auto matches = [](const int val) { return val == 47; };
+
+// Validate dangling story
+STATIC_ASSERT(same_as<decltype(ranges::remove_if(borrowed<false>{}, matches)), ranges::dangling>);
+STATIC_ASSERT(same_as<decltype(ranges::remove_if(borrowed<true>{}, matches)), ranges::subrange<int*>>);
+
+struct instantiator {
+    static constexpr P expected[3] = {{0, 99}, {2, 99}, {4, 99}};
+
+    template <ranges::forward_range Read>
+    static constexpr void call() {
+#if !defined(__clang__) && !defined(__EDG__) // TRANSITION, VSO-938163
+#pragma warning(suppress : 4127) // conditional expression is constant
+        if (!ranges::contiguous_range<Read> || !is_constant_evaluated())
+#endif // TRANSITION, VSO-938163
+        {
+            using ranges::remove_if, ranges::subrange, ranges::equal, ranges::iterator_t;
+
+            size_t projectionCounter = 0;
+            auto projection          = [&projectionCounter](const P& val) {
+                ++projectionCounter;
+                return val.second;
+            };
+
+            { // Validate iterator + sentinel overload
+                P input[5] = {{0, 99}, {1, 47}, {2, 99}, {3, 47}, {4, 99}};
+                Read wrapped_input{input};
+
+                auto result = remove_if(wrapped_input.begin(), wrapped_input.end(), matches, projection);
+                STATIC_ASSERT(same_as<decltype(result), subrange<iterator_t<Read>>>);
+                assert(result.begin() == next(wrapped_input.begin(), 3));
+                assert(result.end() == wrapped_input.end());
+                assert(equal(expected, span{input}.first<3>()));
+                assert(projectionCounter == ranges::size(input));
+            }
+
+            projectionCounter = 0;
+
+            { // Validate range overload
+                P input[5] = {{0, 99}, {1, 47}, {2, 99}, {3, 47}, {4, 99}};
+                Read wrapped_input{input};
+
+                auto result = remove_if(wrapped_input, matches, projection);
+                STATIC_ASSERT(same_as<decltype(result), subrange<iterator_t<Read>>>);
+                assert(result.begin() == next(wrapped_input.begin(), 3));
+                assert(result.end() == wrapped_input.end());
+                assert(equal(expected, span{input}.first<3>()));
+                assert(projectionCounter == ranges::size(input));
+            }
+        }
+    }
+};
+
+int main() {
+    STATIC_ASSERT((test_fwd<instantiator, P>(), true));
+    test_fwd<instantiator, P>();
+}