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+/*!
+@file
+Forward declares `boost::hana::second`.
+
+@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_FWD_SECOND_HPP
+#define BOOST_HANA_FWD_SECOND_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+ //! Returns the second element of a pair.
+ //! @ingroup group-Product
+ //!
+ //! Note that if the `Product` actually stores the elements it contains,
+ //! `hana::second` is required to return a lvalue reference, a lvalue
+ //! reference to const or a rvalue reference to the second element, where
+ //! the type of reference must match that of the pair passed to `second`.
+ //! If the `Product` does not store the elements it contains (i.e. it
+ //! generates them on demand), this requirement is dropped.
+ //!
+ //! Example
+ //! -------
+ //! @include example/second.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+ constexpr auto second = [](auto&& product) -> decltype(auto) {
+ return tag-dispatched;
+ };
+#else
+ template <typename P, typename = void>
+ struct second_impl : second_impl<P, when<true>> { };
+
+ struct second_t {
+ template <typename Pair>
+ constexpr decltype(auto) operator()(Pair&& pair) const;
+ };
+
+ constexpr second_t second{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_SECOND_HPP