| 1 | // Copyright Louis Dionne 2013-2022 |
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| 2 | // Distributed under the Boost Software License, Version 1.0. |
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| 3 | // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
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| 4 | |
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| 5 | #include <boost/hana/assert.hpp> |
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| 6 | #include <boost/hana/equal.hpp> |
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| 7 | #include <boost/hana/not.hpp> |
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| 8 | #include <boost/hana/optional.hpp> |
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| 9 | #include <boost/hana/traits.hpp> |
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| 10 | #include <boost/hana/type.hpp> |
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| 11 | |
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| 12 | #include <type_traits> |
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| 13 | #include <utility> |
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| 14 | namespace hana = boost::hana; |
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| 15 | |
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| 16 | |
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| 17 | template <typename ...> |
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| 18 | using void_t = void; |
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| 19 | |
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| 20 | template <typename T, typename = void> |
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| 21 | struct has_type : std::false_type { }; |
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| 22 | |
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| 23 | template <typename T> |
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| 24 | struct has_type<T, void_t<typename T::type>> |
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| 25 | : std::true_type |
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| 26 | { }; |
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| 27 | |
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| 28 | auto common_type_impl = hana::sfinae([](auto t, auto u) -> hana::type< |
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| 29 | decltype(true ? hana::traits::declval(t) : hana::traits::declval(u)) |
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| 30 | > { return {}; }); |
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| 31 | |
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| 32 | template <typename T, typename U> |
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| 33 | using common_type = decltype(common_type_impl(hana::type_c<T>, hana::type_c<U>)); |
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| 34 | |
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| 35 | BOOST_HANA_CONSTANT_CHECK( |
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| 36 | common_type_impl(hana::type_c<int>, hana::type_c<float>) |
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| 37 | == |
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| 38 | hana::just(hana::type_c<float>) |
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| 39 | ); |
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| 40 | |
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| 41 | static_assert(!has_type<common_type<int, int*>>{}, "" ); |
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| 42 | static_assert(std::is_same<common_type<int, float>::type, float>{}, "" ); |
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| 43 | |
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| 44 | int main() { } |
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| 45 | |
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