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author | DongHun Kwak <dh0128.kwak@samsung.com> | 2016-10-06 10:38:45 +0900 |
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committer | DongHun Kwak <dh0128.kwak@samsung.com> | 2016-10-06 10:39:52 +0900 |
commit | 5cde13f21d36c7224b0e13d11c4b49379ae5210d (patch) | |
tree | e8269ac85a4b0f7d416e2565fa4f451b5cb41351 /boost/hana/front.hpp | |
parent | d9ec475d945d3035377a0d89ed42e382d8988891 (diff) | |
download | boost-5cde13f21d36c7224b0e13d11c4b49379ae5210d.tar.gz boost-5cde13f21d36c7224b0e13d11c4b49379ae5210d.tar.bz2 boost-5cde13f21d36c7224b0e13d11c4b49379ae5210d.zip |
Imported Upstream version 1.61.0
Change-Id: I96a1f878d1e6164f01e9aadd5147f38fca448d90
Signed-off-by: DongHun Kwak <dh0128.kwak@samsung.com>
Diffstat (limited to 'boost/hana/front.hpp')
-rw-r--r-- | boost/hana/front.hpp | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/boost/hana/front.hpp b/boost/hana/front.hpp new file mode 100644 index 0000000000..e8b53de32d --- /dev/null +++ b/boost/hana/front.hpp @@ -0,0 +1,47 @@ +/*! +@file +Defines `boost::hana::front`. + +@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_FRONT_HPP +#define BOOST_HANA_FRONT_HPP + +#include <boost/hana/fwd/front.hpp> + +#include <boost/hana/at.hpp> +#include <boost/hana/concept/iterable.hpp> +#include <boost/hana/config.hpp> +#include <boost/hana/core/dispatch.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! @cond + template <typename Xs> + constexpr decltype(auto) front_t::operator()(Xs&& xs) const { + using It = typename hana::tag_of<Xs>::type; + using Front = BOOST_HANA_DISPATCH_IF(front_impl<It>, + hana::Iterable<It>::value + ); + + #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS + static_assert(hana::Iterable<It>::value, + "hana::front(xs) requires 'xs' to be an Iterable"); + #endif + + return Front::apply(static_cast<Xs&&>(xs)); + } + //! @endcond + + template <typename It, bool condition> + struct front_impl<It, when<condition>> : default_ { + template <typename Xs> + static constexpr decltype(auto) apply(Xs&& xs) + { return hana::at_c<0>(static_cast<Xs&&>(xs)); } + }; +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_FRONT_HPP |