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- // 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() { }
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