Edit: /usr/include/boost/hana/take_front.hpp (2471B)
/*!
@file
Defines `boost::hana::take_front` and `boost::hana::take_front_c`.
@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_TAKE_FRONT_HPP
#define BOOST_HANA_TAKE_FRONT_HPP
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template
constexpr auto take_front_t::operator()(Xs&& xs, N const& n) const {
using S = typename hana::tag_of::type;
using TakeFront = BOOST_HANA_DISPATCH_IF(take_front_impl,
hana::Sequence::value &&
hana::IntegralConstant::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence::value,
"hana::take_front(xs, n) requires 'xs' to be a Sequence");
static_assert(hana::IntegralConstant::value,
"hana::take_front(xs, n) requires 'n' to be an IntegralConstant");
#endif
return TakeFront::apply(static_cast(xs), n);
}
//! @endcond
template
struct take_front_impl> : default_ {
template
static constexpr auto take_front_helper(Xs&& xs, std::index_sequence) {
return hana::make(hana::at_c(static_cast(xs))...);
}
template
static constexpr auto apply(Xs&& xs, N const&) {
constexpr std::size_t n = N::value;
constexpr std::size_t size = decltype(hana::length(xs))::value;
return take_front_helper(static_cast(xs),
std::make_index_sequence<(n < size ? n : size)>{});
}
};
template
struct take_front_c_t {
template
constexpr auto operator()(Xs&& xs) const {
return hana::take_front(static_cast(xs), hana::size_c);
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_TAKE_FRONT_HPP