Modernize ranges::count

stl/inc/algorithm

@@ -606,26 +606,33 @@ namespace ranges {
         _NODISCARD constexpr iter_difference_t<_It> operator()(
             _It _First, _Se _Last, const _Ty& _Val, _Pj _Proj = {}) const {
             _Adl_verify_range(_First, _Last);
+            return _Count_unchecked(
+                _Get_unwrapped(_STD move(_First)), _Get_unwrapped(_STD move(_Last)), _Val, _Pass_fn(_Proj));
+        }
 
-            auto _UFirst                  = _Get_unwrapped(_STD move(_First));
-            const auto _ULast             = _Get_unwrapped(_STD move(_Last));
-            iter_difference_t<_It> _Count = 0;
+        template <input_range _Rng, class _Ty, class _Pj = identity>
+            requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Rng>, _Pj>, const _Ty*>
+        _NODISCARD constexpr range_difference_t<_Rng> operator()(_Rng&& _Range, const _Ty& _Val, _Pj _Proj = {}) const {
+            return _Count_unchecked(_Ubegin(_Range), _Uend(_Range), _Val, _Pass_fn(_Proj));
+        }
+        // clang-format on
+    private:
+        template <class _It, class _Se, class _Ty, class _Pj>
+        _NODISCARD static constexpr iter_difference_t<_It> _Count_unchecked(
+            _It _First, const _Se _Last, const _Ty& _Val, _Pj _Proj) {
+            _STL_INTERNAL_STATIC_ASSERT(input_iterator<_It>);
+            _STL_INTERNAL_STATIC_ASSERT(sentinel_for<_Se, _It>);
+            _STL_INTERNAL_STATIC_ASSERT(indirect_binary_predicate<ranges::equal_to, projected<_It, _Pj>, const _Ty*>);
 
-            for (; _UFirst != _ULast; ++_UFirst) {
-                if (_STD invoke(_Proj, *_UFirst) == _Val) {
+            iter_difference_t<_It> _Count = 0;
+            for (; _First != _Last; ++_First) {
+                if (_STD invoke(_Proj, *_First) == _Val) {
                     ++_Count;
                 }
             }
 
             return _Count;
         }
-
-        template <input_range _Rng, class _Ty, class _Pj = identity>
-            requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Rng>, _Pj>, const _Ty*>
-        _NODISCARD constexpr range_difference_t<_Rng> operator()(_Rng&& _Range, const _Ty& _Val, _Pj _Proj = {}) const {
-            return (*this)(_RANGES begin(_Range), _RANGES end(_Range), _Val, _Pass_fn(_Proj));
-        }
-        // clang-format on
     };
 
     inline constexpr _Count_fn count{_Not_quite_object::_Construct_tag{}};

tests/std/tests/P0896R4_ranges_alg_count/test.cpp

@@ -2,52 +2,40 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <algorithm>
-#include <array>
 #include <cassert>
 #include <concepts>
 #include <ranges>
 #include <utility>
 
 #include <range_algorithm_support.hpp>
 
-constexpr void smoke_test() {
-    using ranges::count;
-    using P                  = std::pair<int, int>;
-    std::array<P, 5> const x = {{{0, 99}, {1, 47}, {2, 99}, {3, 47}, {4, 99}}};
-    using D                  = ranges::range_difference_t<basic_borrowed_range<P const>>;
-
-    {
-        // Validate range overload
-        auto result = count(basic_borrowed_range{x}, 99, get_second);
-        STATIC_ASSERT(std::same_as<decltype(result), D>);
-        assert(result == 3);
-    }
-    {
-        // Validate iterator + sentinel overload
-        basic_borrowed_range wrapped_x{x};
-        auto result = count(wrapped_x.begin(), wrapped_x.end(), 47, get_second);
-        STATIC_ASSERT(std::same_as<decltype(result), D>);
-        assert(result == 2);
-    }
-}
-
-int main() {
-    STATIC_ASSERT((smoke_test(), true));
-    smoke_test();
-}
+using namespace std;
+using P = pair<int, int>;
 
 struct instantiator {
-    template <class In>
-    static void call(In&& in = {}) {
-        ranges::range_value_t<In> const value{};
-        (void) ranges::count(in, value);
-
-        struct type {
-            bool operator==(type const&) const = default;
-        };
-        using Projection = type (*)(std::iter_common_reference_t<ranges::iterator_t<In>>);
-        (void) ranges::count(in, type{}, Projection{});
+    static constexpr P input[5] = {{0, 99}, {1, 47}, {2, 99}, {3, 47}, {4, 99}};
+
+    template <ranges::input_range Read>
+    static constexpr void call() {
+        using ranges::count;
+        { // Validate iterator + sentinel overload
+            Read wrapped_input{input};
+
+            auto result = count(wrapped_input.begin(), wrapped_input.end(), 47, get_second);
+            STATIC_ASSERT(same_as<decltype(result), ranges::range_difference_t<Read>>);
+            assert(result == 2);
+        }
+        { // Validate range overload
+            Read wrapped_input{input};
+
+            auto result = count(wrapped_input, 99, get_second);
+            STATIC_ASSERT(same_as<decltype(result), ranges::range_difference_t<Read>>);
+            assert(result == 3);
+        }
     }
 };
 
-template void test_in<instantiator, const int>();
+int main() {
+    STATIC_ASSERT((test_in<instantiator, P const>(), true));
+    test_in<instantiator, P const>();
+}