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/*!
@file
Defines `boost::hana::value`.
@copyright Louis Dionne 2013-2016
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 BOOST_HANA_VALUE_HPP
#define BOOST_HANA_VALUE_HPP
#include <boost/hana/fwd/value.hpp>
#include <boost/hana/concept/constant.hpp>
#include <boost/hana/concept/integral_constant.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <type_traits>
BOOST_HANA_NAMESPACE_BEGIN
template <typename C, bool condition>
struct value_impl<C, when<condition>> : default_ {
template <typename ...Args>
static constexpr auto apply(Args&& ...args) = delete;
};
template <typename T>
constexpr decltype(auto) value() {
using RawT = typename std::remove_cv<
typename std::remove_reference<T>::type
>::type;
using C = typename hana::tag_of<RawT>::type;
using Value = BOOST_HANA_DISPATCH_IF(
value_impl<C>, hana::Constant<C>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Constant<C>::value,
"hana::value<T>() requires 'T' to be a Constant");
#endif
return Value::template apply<RawT>();
}
template <typename I>
struct value_impl<I, when<hana::IntegralConstant<I>::value>> {
template <typename C>
static constexpr auto apply()
{ return C::value; }
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_VALUE_HPP
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