1 files changed, 44 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/optional/sfinae_friendly_metafunctions.cpp b/src/boost/libs/hana/example/optional/sfinae_friendly_metafunctions.cpp
new file mode 100644
index 000000000..392154b39
--- /dev/null
+++ b/src/boost/libs/hana/example/optional/sfinae_friendly_metafunctions.cpp
@@ -0,0 +1,44 @@
+// 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/assert.hpp>
+#include <boost/hana/equal.hpp>
+#include <boost/hana/not.hpp>
+#include <boost/hana/optional.hpp>
+#include <boost/hana/traits.hpp>
+#include <boost/hana/type.hpp>
+
+#include <type_traits>
+#include <utility>
+namespace hana = boost::hana;
+
+
+template <typename ...>
+using void_t = void;
+
+template <typename T, typename = void>
+struct has_type : std::false_type { };
+
+template <typename T>
+struct has_type<T, void_t<typename T::type>>
+    : std::true_type
+{ };
+
+auto common_type_impl = hana::sfinae([](auto t, auto u) -> hana::type<
+    decltype(true ? hana::traits::declval(t) : hana::traits::declval(u))
+> { return {}; });
+
+template <typename T, typename U>
+using common_type = decltype(common_type_impl(hana::type_c<T>, hana::type_c<U>));
+
+BOOST_HANA_CONSTANT_CHECK(
+  common_type_impl(hana::type_c<int>, hana::type_c<float>)
+    ==
+  hana::just(hana::type_c<float>)
+);
+
+static_assert(!has_type<common_type<int, int*>>{}, "");
+static_assert(std::is_same<common_type<int, float>::type, float>{}, "");
+
+int main() { }