598bfd3f
 Hu Chunming
提交_GLIBCXX_USE_CX...
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/*!
@file
Defines `boost::hana::at` and `boost::hana::at_c`.
Copyright Louis Dionne 2013-2022
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_AT_HPP
#define BOOST_HANA_AT_HPP
#include <boost/hana/fwd/at.hpp>
#include <boost/hana/concept/integral_constant.hpp>
#include <boost/hana/concept/iterable.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/integral_constant.hpp>
#include <cstddef>
namespace boost { namespace hana {
//! @cond
template <typename Xs, typename N>
constexpr decltype(auto) at_t::operator()(Xs&& xs, N const& n) const {
using It = typename hana::tag_of<Xs>::type;
using At = BOOST_HANA_DISPATCH_IF(at_impl<It>,
hana::Iterable<It>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Iterable<It>::value,
"hana::at(xs, n) requires 'xs' to be an Iterable");
static_assert(hana::IntegralConstant<N>::value,
"hana::at(xs, n) requires 'n' to be an IntegralConstant");
#endif
return At::apply(static_cast<Xs&&>(xs), n);
}
//! @endcond
template <typename It, bool condition>
struct at_impl<It, when<condition>> : default_ {
template <typename ...Args>
static constexpr auto apply(Args&& ...) = delete;
};
template <std::size_t n, typename Xs>
constexpr decltype(auto) at_c(Xs&& xs) {
return hana::at(static_cast<Xs&&>(xs), hana::size_t<n>{});
}
}} // end namespace boost::hana
#endif // !BOOST_HANA_AT_HPP
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