1 // Copyright Louis Dionne 2013-2017 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> applyboost::hana::value_impl29 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> applyboost::hana::to_impl40 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 46