Implement N3672, optional<T>.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@189772 91177308-0d34-0410-b5e6-96231b3b80d8

test/utilities/optional/optional.object/optional.object.assign/nullopt_t.pass.cpp

@@ -0,0 +1,63 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <optional>
+
+// optional<T>& operator=(nullopt_t) noexcept;
+
+#include <optional>
+#include <type_traits>
+#include <cassert>
+
+#if _LIBCPP_STD_VER > 11
+
+struct X
+{
+    static bool dtor_called;
+    ~X() {dtor_called = true;}
+};
+
+bool X::dtor_called = false;
+
+#endif  // _LIBCPP_STD_VER > 11
+
+int main()
+{
+#if _LIBCPP_STD_VER > 11
+    {
+        std::optional<int> opt;
+        static_assert(noexcept(opt = std::nullopt) == true, "");
+        opt = std::nullopt;
+        assert(static_cast<bool>(opt) == false);
+    }
+    {
+        std::optional<int> opt(3);
+        opt = std::nullopt;
+        assert(static_cast<bool>(opt) == false);
+    }
+    {
+        std::optional<X> opt;
+        static_assert(noexcept(opt = std::nullopt) == true, "");
+        assert(X::dtor_called == false);
+        opt = std::nullopt;
+        assert(X::dtor_called == false);
+        assert(static_cast<bool>(opt) == false);
+    }
+    {
+        X x;
+        {
+            std::optional<X> opt(x);
+            assert(X::dtor_called == false);
+            opt = std::nullopt;
+            assert(X::dtor_called == true);
+            assert(static_cast<bool>(opt) == false);
+        }
+    }
+#endif  // _LIBCPP_STD_VER > 11
+}