Speculatively implement the PR of ericniebler/stl2#623

CaseyCarter · Apr 26, 2019 · 43bd82d · 43bd82d
1 parent 4ce0f17
commit 43bd82d
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Showing 3 changed files with 33 additions and 16 deletions.
diff --git a/include/stl2/detail/range/concepts.hpp b/include/stl2/detail/range/concepts.hpp
@@ -157,8 +157,12 @@ STL2_OPEN_NAMESPACE {
 
 	template<class Rng>
 	META_CONCEPT ViewableRange =
+#if 1 // This is the PR of https://github.com/ericniebler/stl2/issues/623
+		View<__uncvref<Rng>> || _ForwardingRange<Rng>;
+#else
 		Range<Rng> &&
-		(_RangeImpl<Rng> || View<Rng>);
+		(_RangeImpl<Rng> || View<std::decay_t<Rng>>);
+#endif
 
 	namespace ext {
 		template<Range R>

diff --git a/include/stl2/view/all.hpp b/include/stl2/view/all.hpp
@@ -22,22 +22,29 @@
 STL2_OPEN_NAMESPACE {
 	namespace view {
 		struct __all_fn : detail::__pipeable<__all_fn> {
-			template<Range R>
-			requires View<__f<R>>
-			constexpr auto operator()(R&& r) const
-			noexcept(std::is_nothrow_constructible_v<__f<R>, R>) {
-				return static_cast<R&&>(r);
-			}
+		private:
+			enum : unsigned { __throws = 1, __decay = 2, __ref = 4, __subrange = 6 };
 
-			template<_ForwardingRange R>
-			requires (!View<__uncvref<R>>)
-			constexpr auto operator()(R&& r) const
-			noexcept(std::is_reference_v<R>)
-			{
-				if constexpr (std::is_reference_v<R>) {
-					return ref_view{r};
+			template<ViewableRange _Range>
+			static constexpr unsigned __choose() noexcept {
+				if constexpr (View<__uncvref<_Range>>) {
+					return __decay | std::is_nothrow_constructible_v<__uncvref<_Range>, _Range>;
+				} else if constexpr (std::is_lvalue_reference_v<_Range>) {
+					return __ref | noexcept(ref_view{std::declval<_Range>()});
+				} else {
+					return __subrange | noexcept(subrange{std::declval<_Range>()});
+				}
+			}
+		public:
+			template<ViewableRange _Range, unsigned _Choice = __choose<_Range>()>
+			constexpr auto operator()(_Range&& __r) const noexcept(_Choice & __throws) {
+				constexpr auto __strategy = _Choice & ~__throws;
+				if constexpr (__strategy == __decay) {
+					return static_cast<_Range&&>(__r);
+				} else if constexpr (__strategy == __ref) {
+					return ref_view{__r};
 				} else {
-					return subrange{static_cast<R&&>(r)};
+					return subrange{static_cast<_Range&&>(__r)};
 				}
 			}
 		};

diff --git a/test/view/filter_view.cpp b/test/view/filter_view.cpp
@@ -135,9 +135,15 @@ int main() {
 	}
 
 	{
-		auto yes = [](int){ return true; };
+		auto yes = [](int) { return true; };
 		(void) (view::iota(0) | view::filter(yes));
 	}
 
+	{
+		auto yes = [](int) { return true; };
+		auto const rng = view::iota(0) | view::filter(yes);
+		view::all(rng);
+	}
+
 	return test_result();
 }