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1 | // Copyright Louis Dionne 2013-2016 |
2 | // Distributed under the Boost Software License, Version 1.0. | |
3 | // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
4 | ||
5 | #ifndef TEST_CONCEPT_CONSTANT_MINIMAL_HPP | |
6 | #define TEST_CONCEPT_CONSTANT_MINIMAL_HPP | |
7 | ||
8 | #include <boost/hana/concept/constant.hpp> | |
9 | #include <boost/hana/core/when.hpp> | |
10 | #include <boost/hana/fwd/core/to.hpp> | |
11 | #include <boost/hana/value.hpp> | |
12 | ||
13 | ||
14 | template <typename T> | |
15 | struct minimal_constant_tag { | |
16 | using value_type = T; | |
17 | }; | |
18 | ||
19 | template <typename T, T v> | |
20 | struct minimal_constant { | |
21 | using hana_tag = minimal_constant_tag<T>; | |
22 | static constexpr T value_ = v; | |
23 | }; | |
24 | ||
25 | namespace boost { namespace hana { | |
26 | template <typename T> | |
27 | struct value_impl<minimal_constant_tag<T>> { | |
28 | template <typename N> | |
29 | static constexpr T apply() { return N::value_; } | |
30 | }; | |
31 | ||
32 | template <typename T, typename C> | |
33 | struct to_impl<minimal_constant_tag<T>, C, hana::when< | |
34 | hana::Constant<C>::value && | |
35 | hana::is_convertible<typename C::value_type, T>::value | |
36 | >> | |
37 | : hana::embedding<hana::is_embedded<typename C::value_type, T>::value> | |
38 | { | |
39 | template <typename N> | |
40 | static constexpr auto apply(N const&) | |
41 | { return minimal_constant<T, hana::value<N>()>{}; } | |
42 | }; | |
43 | }} // end namespace boost::hana | |
44 | ||
45 | #endif // !TEST_CONCEPT_CONSTANT_MINIMAL_HPP |