1 files changed, 41 insertions, 0 deletions
diff --git a/src/boost/libs/hana/test/tuple/usability_of_types.cpp b/src/boost/libs/hana/test/tuple/usability_of_types.cpp
new file mode 100644
index 000000000..261b47ad0
--- /dev/null
+++ b/src/boost/libs/hana/test/tuple/usability_of_types.cpp
@@ -0,0 +1,41 @@
+// Copyright Louis Dionne 2013-2017
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+#include <boost/hana/at.hpp>
+#include <boost/hana/back.hpp>
+#include <boost/hana/front.hpp>
+#include <boost/hana/integral_constant.hpp>
+#include <boost/hana/tuple.hpp>
+#include <boost/hana/type.hpp>
+
+#include <type_traits>
+namespace hana = boost::hana;
+
+
+// The fact that a reference to a `type<...>` is returned from `front(types)`
+// and friends used to break the `decltype(front(types))::type` pattern,
+// because we would be trying to fetch `::type` inside a reference. To work
+// around this, a unary `operator+` turning a lvalue `type` into a rvalue
+// `type` was added.
+
+struct T; struct U; struct V;
+
+int main() {
+    auto check = [](auto types) {
+        static_assert(std::is_same<
+            typename decltype(+hana::front(types))::type, T
+        >{}, "");
+
+        static_assert(std::is_same<
+            typename decltype(+hana::at(types, hana::size_c<1>))::type, U
+        >{}, "");
+
+        static_assert(std::is_same<
+            typename decltype(+hana::back(types))::type, V
+        >{}, "");
+    };
+
+    check(hana::make_tuple(hana::type_c<T>, hana::type_c<U>, hana::type_c<V>));
+    check(hana::tuple_t<T, U, V>);
+}