<ranges>: Fix zip_transform_view by not using possibly ill-formed…

… static data member (#4416)
microsoft · Feb 27, 2024 · 017bc35 · 017bc35
1 parent 605c733
commit 017bc35
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Showing 2 changed files with 24 additions and 5 deletions.
diff --git a/stl/inc/ranges b/stl/inc/ranges
@@ -8582,6 +8582,10 @@ namespace ranges {
         _EXPORT_STD inline constexpr _Zip_fn zip{};
     } // namespace views
 
+    template <class _Func, class... _ViewTypes>
+    concept _Can_const_iterate_zip_transform_view =
+        range<const zip_view<_ViewTypes...>> && regular_invocable<const _Func&, range_reference_t<const _ViewTypes>...>;
+
     _EXPORT_STD template <class _Func, class... _ViewTypes>
         requires _Zip_transform_constraints<_Func, _ViewTypes...>
     class zip_transform_view : public view_interface<zip_transform_view<_Func, _ViewTypes...>> {
@@ -8833,9 +8837,6 @@ namespace ranges {
             }
         }
 
-        static constexpr bool _Enable_const_begin_end =
-            (range<const _Inner_view> && regular_invocable<const _Func&, range_reference_t<const _ViewTypes>...>);
-
     public:
         zip_transform_view() = default;
 
@@ -8849,7 +8850,7 @@ namespace ranges {
         }
 
         _NODISCARD constexpr auto begin() const noexcept(noexcept(_Iterator<true>{*this, _Zip.begin()})) // strengthened
-            requires _Enable_const_begin_end
+            requires _Can_const_iterate_zip_transform_view<_Func, _ViewTypes...>
         {
             return _Iterator<true>{*this, _Zip.begin()};
         }
@@ -8863,7 +8864,7 @@ namespace ranges {
         }
 
         _NODISCARD constexpr auto end() const noexcept(_Is_end_noexcept<true>()) // strengthened
-            requires _Enable_const_begin_end
+            requires _Can_const_iterate_zip_transform_view<_Func, _ViewTypes...>
         {
             if constexpr (common_range<const _Inner_view>) {
                 return _Iterator<true>{*this, _Zip.end()};

diff --git a/tests/std/tests/P2321R2_views_zip_transform/test.cpp b/tests/std/tests/P2321R2_views_zip_transform/test.cpp
@@ -806,6 +806,20 @@ constexpr bool validate_empty_ranges() {
     return true;
 }
 
+// Also test GH-4414: "<ranges>: zip_transform does not accept non const iterable ranges"
+constexpr bool test_gh_4414() {
+    auto evens_and_odds = views::zip_transform([](int even, int odd) { return even + odd; },
+        views::iota(0, 10) | views::filter([](int i) { return i % 2 == 0; }),
+        views::iota(0, 10) | views::filter([](int i) { return i % 2 != 0; }));
+
+    using ZippedTransformed = decltype(evens_and_odds);
+    STATIC_ASSERT(ranges::range<ZippedTransformed>);
+    STATIC_ASSERT(!ranges::range<const ZippedTransformed>);
+
+    constexpr int expected_results[]{1, 5, 9, 13, 17};
+    return ranges::equal(expected_results, evens_and_odds);
+}
+
 int main() {
     // Empty RangeTypes... parameter pack
     {
@@ -858,6 +872,10 @@ int main() {
         test_one(three_element_transform_closure, three_range_transform_results_array, test_element_array_one,
             test_element_array_two, test_element_array_three);
     }
+    {
+        STATIC_ASSERT(test_gh_4414());
+        assert(test_gh_4414());
+    }
 
     return 0;
 }