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- /*!
- @file
- Defines `boost::hana::tag_of` and `boost::hana::tag_of_t`.
- @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 BOOST_HANA_CORE_TAG_OF_HPP
- #define BOOST_HANA_CORE_TAG_OF_HPP
- #include <boost/hana/fwd/core/tag_of.hpp>
- #include <boost/hana/config.hpp>
- #include <boost/hana/core/when.hpp>
- BOOST_HANA_NAMESPACE_BEGIN
- //! @cond
- template <typename T, typename>
- struct tag_of : tag_of<T, when<true>> { };
- //! @endcond
- namespace core_detail {
- template <typename ...>
- struct is_valid { static constexpr bool value = true; };
- }
- template <typename T, bool condition>
- struct tag_of<T, when<condition>> {
- using type = T;
- };
- template <typename T>
- struct tag_of<T, when<
- core_detail::is_valid<typename T::hana_tag>::value
- >> {
- using type = typename T::hana_tag;
- };
- template <typename T> struct tag_of<T const> : tag_of<T> { };
- template <typename T> struct tag_of<T volatile> : tag_of<T> { };
- template <typename T> struct tag_of<T const volatile> : tag_of<T> { };
- template <typename T> struct tag_of<T&> : tag_of<T> { };
- template <typename T> struct tag_of<T&&> : tag_of<T> { };
- BOOST_HANA_NAMESPACE_END
- #endif // !BOOST_HANA_CORE_TAG_OF_HPP
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