diff options
Diffstat (limited to 'src/boost/libs/hana/example/optional/sfinae_friendly_metafunctions.cpp')
-rw-r--r-- | src/boost/libs/hana/example/optional/sfinae_friendly_metafunctions.cpp | 44 |
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() { } |