Implement LWG 2773 - std::ignore should be constexpr.

In addition to the PR for LWG 2773 this patch also ensures
that each of std::ignores constructors or assignment operators
are constexpr.

llvm-svn: 294165

1 files changed, 56 insertions, 0 deletions

diff --git a/libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp b/libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp
new file mode 100644
index 00000000000..8dae3a5dcb0
--- /dev/null
+++ b/libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp
@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// <tuple>
+
+// constexpr unspecified ignore;
+
+// UNSUPPORTED: c++98, c++03
+
+#include <tuple>
+#include <cassert>
+
+#include "test_macros.h"
+
+constexpr bool test_ignore_constexpr()
+{
+#if TEST_STD_VER > 11
+    { // Test that std::ignore provides constexpr converting assignment.
+        auto& res = (std::ignore = 42);
+        assert(&res == &std::ignore);
+    }
+    { // Test that std::ignore provides constexpr copy/move constructors
+        auto copy = std::ignore;
+        auto moved = std::move(copy);
+        ((void)moved);
+    }
+    { // Test that std::ignore provides constexpr copy/move assignment
+        auto copy = std::ignore;
+        copy = std::ignore;
+        auto moved = std::ignore;
+        moved = std::move(copy);
+    }
+#endif
+    return true;
+}
+
+int main() {
+    {
+        constexpr auto& ignore_v = std::ignore;
+        ((void)ignore_v);
+    }
+    {
+        static_assert(test_ignore_constexpr(), "");
+    }
+#if defined(_LIBCPP_VERSION)
+    {
+        static_assert(std::is_trivial<decltype(std::ignore)>::value, "");
+    }
+#endif
+}