| 1 | /*! |
|---|---|
| 2 | @file |
| 3 | Defines `boost::hana::value`. |
| 4 | |
| 5 | Copyright Louis Dionne 2013-2022 |
| 6 | Distributed under the Boost Software License, Version 1.0. |
| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
| 8 | */ |
| 9 | |
| 10 | #ifndef BOOST_HANA_VALUE_HPP |
| 11 | #define BOOST_HANA_VALUE_HPP |
| 12 | |
| 13 | #include <boost/hana/fwd/value.hpp> |
| 14 | |
| 15 | #include <boost/hana/concept/constant.hpp> |
| 16 | #include <boost/hana/concept/integral_constant.hpp> |
| 17 | #include <boost/hana/config.hpp> |
| 18 | #include <boost/hana/core/dispatch.hpp> |
| 19 | |
| 20 | #include <type_traits> |
| 21 | |
| 22 | |
| 23 | namespace boost { namespace hana { |
| 24 | template <typename C, bool condition> |
| 25 | struct value_impl<C, when<condition>> : default_ { |
| 26 | template <typename ...Args> |
| 27 | static constexpr auto apply(Args&& ...args) = delete; |
| 28 | }; |
| 29 | |
| 30 | template <typename T> |
| 31 | constexpr decltype(auto) value() { |
| 32 | using RawT = typename std::remove_cv< |
| 33 | typename std::remove_reference<T>::type |
| 34 | >::type; |
| 35 | using C = typename hana::tag_of<RawT>::type; |
| 36 | using Value = BOOST_HANA_DISPATCH_IF( |
| 37 | value_impl<C>, hana::Constant<C>::value |
| 38 | ); |
| 39 | |
| 40 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS |
| 41 | static_assert(hana::Constant<C>::value, |
| 42 | "hana::value<T>() requires 'T' to be a Constant"); |
| 43 | #endif |
| 44 | |
| 45 | return Value::template apply<RawT>(); |
| 46 | } |
| 47 | |
| 48 | template <typename I> |
| 49 | struct value_impl<I, when<hana::IntegralConstant<I>::value>> { |
| 50 | template <typename C> |
| 51 | static constexpr auto apply() |
| 52 | { return C::value; } |
| 53 | }; |
| 54 | }} // end namespace boost::hana |
| 55 | |
| 56 | #endif // !BOOST_HANA_VALUE_HPP |
| 57 |