Implement ranges::lexicographical_compare

stl/inc/algorithm

@@ -8237,6 +8237,59 @@ namespace ranges {
     };
 
     inline constexpr _Clamp_fn clamp{_Not_quite_object::_Construct_tag{}};
+
+    // VARIABLE ranges::lexicographical_compare
+    class _Lexicographical_compare_fn : private _Not_quite_object {
+    public:
+        using _Not_quite_object::_Not_quite_object;
+
+        template <input_iterator _It1, sentinel_for<_It1> _Se1, input_iterator _It2, sentinel_for<_It2> _Se2,
+            class _Pj1 = identity, class _Pj2 = identity,
+            indirect_strict_weak_order<projected<_It1, _Pj1>, projected<_It2, _Pj2>> _Pr = ranges::less>
+        _NODISCARD constexpr bool operator()(_It1 _First1, _Se1 _Last1, _It2 _First2, _Se2 _Last2, _Pr _Pred = {},
+            _Pj1 _Proj1 = {}, _Pj2 _Proj2 = {}) const {
+            _Adl_verify_range(_First1, _Last1);
+            _Adl_verify_range(_First2, _Last2);
+
+            return _Lexicographical_compare_unchecked(_Get_unwrapped(_STD move(_First1)),
+                _Get_unwrapped(_STD move(_Last1)), _Get_unwrapped(_STD move(_First2)),
+                _Get_unwrapped(_STD move(_Last2)), _Pass_fn(_Pred), _Pass_fn(_Proj1), _Pass_fn(_Proj2));
+        }
+
+        template <input_range _Rng1, input_range _Rng2, class _Pj1 = identity, class _Pj2 = identity,
+            indirect_strict_weak_order<projected<iterator_t<_Rng1>, _Pj1>, projected<iterator_t<_Rng2>, _Pj2>> _Pr =
+                ranges::less>
+        _NODISCARD constexpr bool operator()(
+            _Rng1&& _Range1, _Rng2&& _Range2, _Pr _Pred = {}, _Pj1 _Proj1 = {}, _Pj2 _Proj2 = {}) const {
+            return _Lexicographical_compare_unchecked(_Ubegin(_Range1), _Uend(_Range1), _Ubegin(_Range2),
+                _Uend(_Range2), _Pass_fn(_Pred), _Pass_fn(_Proj1), _Pass_fn(_Proj2));
+        }
+
+    private:
+        template <class _It1, class _Se1, class _It2, class _Se2, class _Pr, class _Pj1, class _Pj2>
+        _NODISCARD static constexpr bool _Lexicographical_compare_unchecked(
+            _It1 _First1, _Se1 _Last1, _It2 _First2, _Se2 _Last2, _Pr _Pred, _Pj1 _Proj1, _Pj2 _Proj2) {
+            _STL_INTERNAL_STATIC_ASSERT(input_iterator<_It1>);
+            _STL_INTERNAL_STATIC_ASSERT(sentinel_for<_Se1, _It1>);
+            _STL_INTERNAL_STATIC_ASSERT(input_iterator<_It2>);
+            _STL_INTERNAL_STATIC_ASSERT(sentinel_for<_Se2, _It2>);
+            _STL_INTERNAL_STATIC_ASSERT(indirect_strict_weak_order<_Pr, projected<_It1, _Pj1>, projected<_It2, _Pj2>>);
+
+            for (;; ++_First1, (void) ++_First2) {
+                if (_First2 == _Last2) {
+                    return false;
+                } else if (_First1 == _Last1) {
+                    return true;
+                } else if (_STD invoke(_Pred, _STD invoke(_Proj1, *_First1), _STD invoke(_Proj2, *_First2))) {
+                    return true;
+                } else if (_STD invoke(_Pred, _STD invoke(_Proj2, *_First2), _STD invoke(_Proj1, *_First1))) {
+                    return false;
+                }
+            }
+        }
+    };
+
+    inline constexpr _Lexicographical_compare_fn lexicographical_compare{_Not_quite_object::_Construct_tag{}};
 } // namespace ranges
 #endif // __cpp_lib_concepts
 #endif // _HAS_CXX17

tests/std/test.lst

@@ -262,6 +262,7 @@ tests\P0896R4_ranges_alg_generate_n
 tests\P0896R4_ranges_alg_heap
 tests\P0896R4_ranges_alg_is_permutation
 tests\P0896R4_ranges_alg_is_sorted
+tests\P0896R4_ranges_alg_lexi
 tests\P0896R4_ranges_alg_minmax
 tests\P0896R4_ranges_alg_mismatch
 tests\P0896R4_ranges_alg_move

tests/std/tests/P0896R4_ranges_alg_lexi/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_lexi/test.cpp

@@ -0,0 +1,123 @@
+// 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>;
+
+struct instantiator {
+    static constexpr P left[]          = {{0, 10}, {1, 20}, {2, 30}};
+    static constexpr P right_shorter[] = {{300, 0}, {200, 1}};
+    static constexpr P right_longer[]  = {{300, 0}, {200, 1}, {100, 2}, {0, 3}};
+    static constexpr P right_less[]    = {{300, 0}, {200, 1}, {100, 1}};
+    static constexpr P right_equal[]   = {{300, 0}, {200, 1}, {100, 2}};
+    static constexpr P right_greater[] = {{300, 0}, {200, 1}, {100, 3}};
+
+    template <class In1, class In2>
+    static constexpr void call() {
+        using ranges::lexicographical_compare, ranges::less;
+
+        // Validate range overload
+        {
+            In1 range1{left};
+            In2 range2{right_shorter};
+            const same_as<bool> auto result = lexicographical_compare(range1, range2, less{}, get_first, get_second);
+            assert(!result);
+        }
+        {
+            In1 range1{left};
+            In2 range2{right_longer};
+            const same_as<bool> auto result = lexicographical_compare(range1, range2, less{}, get_first, get_second);
+            assert(result);
+        }
+        {
+            In1 range1{left};
+            In2 range2{right_less};
+            const same_as<bool> auto result = lexicographical_compare(range1, range2, less{}, get_first, get_second);
+            assert(!result);
+        }
+        {
+            In1 range1{left};
+            In2 range2{right_equal};
+            const same_as<bool> auto result = lexicographical_compare(range1, range2, less{}, get_first, get_second);
+            assert(!result);
+        }
+        {
+            In1 range1{left};
+            In2 range2{right_greater};
+            const same_as<bool> auto result = lexicographical_compare(range1, range2, less{}, get_first, get_second);
+            assert(result);
+        }
+
+        // Validate iterator overload
+        {
+            In1 range1{left};
+            In2 range2{right_shorter};
+            const same_as<bool> auto result = lexicographical_compare(
+                range1.begin(), range1.end(), range2.begin(), range2.end(), less{}, get_first, get_second);
+            assert(!result);
+        }
+        {
+            In1 range1{left};
+            In2 range2{right_longer};
+            const same_as<bool> auto result = lexicographical_compare(
+                range1.begin(), range1.end(), range2.begin(), range2.end(), less{}, get_first, get_second);
+            assert(result);
+        }
+        {
+            In1 range1{left};
+            In2 range2{right_less};
+            const same_as<bool> auto result = lexicographical_compare(
+                range1.begin(), range1.end(), range2.begin(), range2.end(), less{}, get_first, get_second);
+            assert(!result);
+        }
+        {
+            In1 range1{left};
+            In2 range2{right_equal};
+            const same_as<bool> auto result = lexicographical_compare(
+                range1.begin(), range1.end(), range2.begin(), range2.end(), less{}, get_first, get_second);
+            assert(!result);
+        }
+        {
+            In1 range1{left};
+            In2 range2{right_greater};
+            const same_as<bool> auto result = lexicographical_compare(
+                range1.begin(), range1.end(), range2.begin(), range2.end(), less{}, get_first, get_second);
+            assert(result);
+        }
+    }
+};
+
+#ifdef TEST_EVERYTHING
+int main() {
+    // No constexpr tests here: we hit the constexpr step limits too quickly.
+    test_in_in<instantiator, const P, const P>();
+}
+#else // ^^^ test all range combinations / test only interesting combinations vvv
+template <test::ProxyRef IsProxy>
+using range_type = test::range<input_iterator_tag, const P, test::Sized::no, test::CanDifference::no, test::Common::no,
+    test::CanCompare::no, IsProxy>;
+
+constexpr void run_tests() {
+    // The algorithm is very much oblivious to any properties above the minimum requirements: category, size,
+    // difference, none of it matters. Let's test input ranges with and without proxy references.
+    using test::ProxyRef;
+
+    instantiator::call<range_type<ProxyRef::yes>, range_type<ProxyRef::yes>>();
+    instantiator::call<range_type<ProxyRef::yes>, range_type<ProxyRef::no>>();
+    instantiator::call<range_type<ProxyRef::no>, range_type<ProxyRef::yes>>();
+    instantiator::call<range_type<ProxyRef::no>, range_type<ProxyRef::no>>();
+}
+
+int main() {
+    STATIC_ASSERT((run_tests(), true));
+    run_tests();
+}
+#endif // TEST_EVERYTHING