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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)
#ifndef TEST_CONCEPT_CONSTANT_MINIMAL_HPP
#define TEST_CONCEPT_CONSTANT_MINIMAL_HPP
#include <boost/hana/concept/constant.hpp>
#include <boost/hana/core/when.hpp>
#include <boost/hana/fwd/core/to.hpp>
#include <boost/hana/value.hpp>
template <typename T>
struct minimal_constant_tag {
using value_type = T;
};
template <typename T, T v>
struct minimal_constant {
using hana_tag = minimal_constant_tag<T>;
static constexpr T value_ = v;
};
namespace boost { namespace hana {
template <typename T>
struct value_impl<minimal_constant_tag<T>> {
template <typename N>
static constexpr T apply() { return N::value_; }
};
template <typename T, typename C>
struct to_impl<minimal_constant_tag<T>, C, hana::when<
hana::Constant<C>::value &&
hana::is_convertible<typename C::value_type, T>::value
>>
: hana::embedding<hana::is_embedded<typename C::value_type, T>::value>
{
template <typename N>
static constexpr auto apply(N const&)
{ return minimal_constant<T, hana::value<N>()>{}; }
};
}} // end namespace boost::hana
#endif // !TEST_CONCEPT_CONSTANT_MINIMAL_HPP
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