Specialize _Non_propagating_cache and fix test

microsoft · Jul 3, 2021 · 49bf9a3 · 49bf9a3
1 parent 92ce96e
commit 49bf9a3
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Showing 2 changed files with 79 additions and 6 deletions.
diff --git a/stl/inc/ranges b/stl/inc/ranges
@@ -621,10 +621,12 @@ namespace ranges {
     };
 
     // CLASS TEMPLATE ranges::_Non_propagating_cache
-    // clang-format off
     template <class _Ty>
-        requires is_object_v<_Ty>
-    class _Non_propagating_cache { // a simplified optional that augments copy_constructible types with full copyability
+    concept _Objectable = is_object_v<_Ty>;
+
+    // clang-format off
+    template <_Objectable _Ty>
+    class _Non_propagating_cache { // a simplified optional that resets on copy / move
         // clang-format on
     public:
         constexpr _Non_propagating_cache() noexcept : _Dummy{} {}
@@ -710,6 +712,72 @@ namespace ranges {
         bool _Engaged = false;
     };
 
+    // clang-format off
+    template <_Objectable _Ty>
+        requires is_trivially_destructible_v<_Ty>
+    class _Non_propagating_cache<_Ty> { // provide the same API more efficiently for
+        // clang-format on
+    public:
+        constexpr _Non_propagating_cache() noexcept : _Dummy{} {}
+
+        template <class... _Types>
+        constexpr _Non_propagating_cache(in_place_t, _Types&&... _Args) noexcept(
+            is_nothrow_constructible_v<_Ty, _Types...>) // strengthened
+            : _Val(_STD forward<_Types>(_Args)...), _Engaged{true} {}
+
+        constexpr _Non_propagating_cache(const _Non_propagating_cache&) noexcept {}
+
+        constexpr _Non_propagating_cache(_Non_propagating_cache&& _Other) noexcept {
+            _Other._Engaged = false;
+        }
+
+        constexpr _Non_propagating_cache& operator=(const _Non_propagating_cache& _Other) noexcept {
+            if (_STD addressof(_Other) == this) {
+                return *this;
+            }
+
+            _Engaged = false;
+
+            return *this;
+        }
+
+        _CONSTEXPR20_DYNALLOC _Non_propagating_cache& operator=(_Non_propagating_cache&& _Other) noexcept {
+            _Engaged        = false;
+            _Other._Engaged = false;
+
+            return *this;
+        }
+
+        constexpr explicit operator bool() const noexcept {
+            return _Engaged;
+        }
+
+        _NODISCARD constexpr _Ty& operator*() noexcept {
+            _STL_INTERNAL_CHECK(_Engaged);
+            return _Val;
+        }
+        _NODISCARD constexpr const _Ty& operator*() const noexcept {
+            _STL_INTERNAL_CHECK(_Engaged);
+            return _Val;
+        }
+
+        template <class _It>
+        constexpr _Ty& _Emplace_deref(_It& _Iter) noexcept(noexcept(_Ty(*_Iter))) /* strengthened */ {
+            _Engaged = false;
+            _Construct_in_place(_Val, *_Iter);
+            _Engaged = true;
+
+            return _Val;
+        }
+
+    private:
+        union {
+            _Nontrivial_dummy_type _Dummy;
+            _Ty _Val;
+        };
+        bool _Engaged = false;
+    };
+
     // CLASS TEMPLATE ranges::empty_view
     // clang-format off
     template <class _Ty>

diff --git a/tests/std/tests/P0896R4_views_join/test.cpp b/tests/std/tests/P0896R4_views_join/test.cpp
@@ -478,9 +478,9 @@ int main() {
         static_assert(test_one(sp, expected));
         test_one(sp, expected);
     }
-    { // ...prvalue
-        static_assert(test_one(array<string, 5>{{{}, "Hello ", {}, "World!", {}}}, expected));
-        test_one(array<string, 5>{{{}, "Hello ", {}, "World!", {}}}, expected);
+    { // ...copyable rvalue
+        static_assert(test_one(array<string_view, 5>{{{}, "Hello "sv, {}, "World!"sv, {}}}, expected));
+        test_one(array<string_view, 5>{{{}, "Hello "sv, {}, "World!"sv, {}}}, expected);
     }
     // ... move-only
     test_move_only_views();
@@ -513,6 +513,11 @@ int main() {
         assert(ranges::equal(joined, result));
     }
 
+    { // P2328 range of prvalue ranges
+        auto joined = views::iota(0, 5) | views::transform([](int i) { return std::to_string(i); }) | views::join;
+        assert(ranges::equal(joined, "01234"sv));
+    }
+
 #if defined(__clang__) || defined(__EDG__) // TRANSITION, VSO-934264
     STATIC_ASSERT(instantiation_test());
 #endif // TRANSITION, VSO-934264