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Diffstat (limited to 'boost/hana/second.hpp')
-rw-r--r-- | boost/hana/second.hpp | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/boost/hana/second.hpp b/boost/hana/second.hpp new file mode 100644 index 0000000000..e5c28c9036 --- /dev/null +++ b/boost/hana/second.hpp @@ -0,0 +1,45 @@ +/*! +@file +Defines `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_SECOND_HPP +#define BOOST_HANA_SECOND_HPP + +#include <boost/hana/fwd/second.hpp> + +#include <boost/hana/concept/product.hpp> +#include <boost/hana/config.hpp> +#include <boost/hana/core/dispatch.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! @cond + template <typename Pair> + constexpr decltype(auto) second_t::operator()(Pair&& pair) const { + using P = typename hana::tag_of<Pair>::type; + using Second = BOOST_HANA_DISPATCH_IF(second_impl<P>, + hana::Product<P>::value + ); + + #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS + static_assert(hana::Product<P>::value, + "hana::second(pair) requires 'pair' to be a Product"); + #endif + + return Second::apply(static_cast<Pair&&>(pair)); + } + //! @endcond + + template <typename P, bool condition> + struct second_impl<P, when<condition>> : default_ { + template <typename ...Args> + static constexpr auto apply(Args&& ...) = delete; + }; +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_SECOND_HPP |