Merge pull request #160 from mlogan/master

Fix the noexcept specifications for move assignment and conversion.

Author: artemp

Makefile

@@ -99,7 +99,7 @@ out/%.o: test/t/%.cpp Makefile $(ALL_HEADERS)
 	mkdir -p ./out
 	$(CXX) -c -o $@ $< -Iinclude -isystem test/include $(FINAL_CXXFLAGS)
 
-out/unit: out/unit.o out/binary_visitor_1.o out/binary_visitor_2.o out/binary_visitor_3.o out/binary_visitor_4.o out/binary_visitor_5.o out/binary_visitor_6.o out/issue21.o out/issue122.o out/mutating_visitor.o out/optional.o out/recursive_wrapper.o out/sizeof.o out/unary_visitor.o out/variant.o out/variant_alternative.o
+out/unit: out/unit.o out/binary_visitor_1.o out/binary_visitor_2.o out/binary_visitor_3.o out/binary_visitor_4.o out/binary_visitor_5.o out/binary_visitor_6.o out/issue21.o out/issue122.o out/mutating_visitor.o out/optional.o out/recursive_wrapper.o out/sizeof.o out/unary_visitor.o out/variant.o out/variant_alternative.o out/nothrow_move.o
 	mkdir -p ./out
 	$(CXX) -o $@ $^ $(LDFLAGS)
 

include/mapbox/variant.hpp

@@ -637,6 +637,9 @@ class variant
 
 public:
     VARIANT_INLINE variant<Types...>& operator=(variant<Types...>&& other)
+        // note we check for nothrow-constructible, not nothrow-assignable, since
+        // move_assign uses move-construction via placement new.
+        noexcept(detail::conjunction<std::is_nothrow_move_constructible<Types>...>::value)
     {
         move_assign(std::move(other));
         return *this;
@@ -650,8 +653,13 @@ class variant
 
     // conversions
     // move-assign
-    template <typename T>
-    VARIANT_INLINE variant<Types...>& operator=(T&& rhs) noexcept
+    template <typename T, typename Traits = detail::value_traits<T, Types...>,
+              typename Enable = typename std::enable_if<Traits::is_valid && !std::is_same<variant<Types...>, typename Traits::value_type>::value>::type >
+    VARIANT_INLINE variant<Types...>& operator=(T&& rhs)
+        // not that we check is_nothrow_constructible<T>, not is_nothrow_move_assignable<T>,
+        // since we construct a temporary
+        noexcept(std::is_nothrow_constructible<typename Traits::target_type, T&&>::value
+                 && std::is_nothrow_move_assignable<variant<Types...>>::value)
     {
         variant<Types...> temp(std::forward<T>(rhs));
         move_assign(std::move(temp));

test/t/nothrow_move.cpp

@@ -0,0 +1,66 @@
+#include <typeinfo>
+#include <utility>
+
+#include <mapbox/variant.hpp>
+
+using namespace mapbox;
+
+namespace test {
+
+struct t_noexcept_true_1 {
+  t_noexcept_true_1(t_noexcept_true_1&&) noexcept = default;
+  t_noexcept_true_1& operator=(t_noexcept_true_1&&) noexcept = default;
+};
+
+struct t_noexcept_true_2 {
+  t_noexcept_true_2(t_noexcept_true_2&&) noexcept = default;
+  t_noexcept_true_2& operator=(t_noexcept_true_2&&) noexcept = default;
+};
+
+struct t_noexcept_false_1 {
+  t_noexcept_false_1(t_noexcept_false_1&&) noexcept(false) {}
+  t_noexcept_false_1& operator=(t_noexcept_false_1&&) noexcept(false) { return *this; }
+};
+
+using should_be_no_throw_copyable = util::variant<t_noexcept_true_1, t_noexcept_true_2>;
+static_assert(std::is_nothrow_move_assignable<should_be_no_throw_copyable>::value,
+              "variants with no-throw move assignable types should be "
+              "no-throw move nothrow assignable");
+
+using should_be_no_throw_assignable = util::variant<t_noexcept_true_1, t_noexcept_true_2>;
+static_assert(std::is_nothrow_move_constructible<should_be_no_throw_assignable>::value,
+              "variants with no-throw move assignable types should be "
+              "no-throw move nothrow assignable");
+
+using should_not_be_no_throw_copyable = util::variant<t_noexcept_true_1, t_noexcept_false_1>;
+static_assert(not std::is_nothrow_move_assignable<should_not_be_no_throw_copyable>::value,
+              "variants with no-throw move assignable types should be "
+              "no-throw move nothrow assignable");
+
+using should_not_be_no_throw_assignable = util::variant<t_noexcept_true_1, t_noexcept_false_1>;
+static_assert(not std::is_nothrow_move_constructible<should_not_be_no_throw_assignable>::value,
+              "variants with no-throw move assignable types should be "
+              "no-throw move nothrow assignable");
+
+
+// this type cannot be nothrow converted from either of its types, even the nothrow moveable one,
+// because the conversion operator moves the whole variant.
+using convertable_test_type = util::variant<t_noexcept_true_1, t_noexcept_false_1>;
+
+// this type can be nothrow converted from either of its types.
+using convertable_test_type_2 = util::variant<t_noexcept_true_1, t_noexcept_true_2>;
+
+static_assert(not std::is_nothrow_assignable<convertable_test_type, t_noexcept_true_1>::value,
+              "variants with noexcept(true) move constructible types should be nothrow-convertible "
+              "from those types only IF the variant itself is nothrow_move_assignable");
+
+static_assert(not std::is_nothrow_assignable<convertable_test_type, t_noexcept_false_1>::value,
+              "variants with noexcept(false) move constructible types should not be nothrow-convertible "
+              "from those types");
+
+static_assert(std::is_nothrow_assignable<convertable_test_type_2, t_noexcept_true_2>::value,
+              "variants with noexcept(true) move constructible types should be nothrow-convertible "
+              "from those types only IF the variant itself is nothrow_move_assignable");
+
+
+} // namespace test