| 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 | #ifndef TEST_CONCEPT_CONSTANT_MINIMAL_HPP |
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| 6 | #define TEST_CONCEPT_CONSTANT_MINIMAL_HPP |
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| 7 | |
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| 8 | #include <boost/hana/concept/constant.hpp> |
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| 9 | #include <boost/hana/core/when.hpp> |
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| 10 | #include <boost/hana/fwd/core/to.hpp> |
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| 11 | #include <boost/hana/value.hpp> |
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| 12 | |
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| 13 | |
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| 14 | template <typename T> |
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| 15 | struct minimal_constant_tag { |
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| 16 | using value_type = T; |
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| 17 | }; |
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| 18 | |
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| 19 | template <typename T, T v> |
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| 20 | struct minimal_constant { |
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| 21 | using hana_tag = minimal_constant_tag<T>; |
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| 22 | static constexpr T value_ = v; |
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| 23 | }; |
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| 24 | |
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| 25 | namespace boost { namespace hana { |
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| 26 | template <typename T> |
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| 27 | struct value_impl<minimal_constant_tag<T>> { |
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| 28 | template <typename N> |
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| 29 | static constexpr T apply() { return N::value_; } |
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| 30 | }; |
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| 31 | |
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| 32 | template <typename T, typename C> |
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| 33 | struct to_impl<minimal_constant_tag<T>, C, hana::when< |
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| 34 | hana::Constant<C>::value && |
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| 35 | hana::is_convertible<typename C::value_type, T>::value |
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| 36 | >> |
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| 37 | : hana::embedding<hana::is_embedded<typename C::value_type, T>::value> |
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| 38 | { |
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| 39 | template <typename N> |
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| 40 | static constexpr auto apply(N const&) |
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| 41 | { return minimal_constant<T, hana::value<N>()>{}; } |
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| 42 | }; |
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| 43 | }} // end namespace boost::hana |
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| 44 | |
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| 45 | #endif // !TEST_CONCEPT_CONSTANT_MINIMAL_HPP |
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| 46 | |
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