Edit: /usr/include/boost/hana/front.hpp (1315B)
/*!
@file
Defines `boost::hana::front`.
@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_FRONT_HPP
#define BOOST_HANA_FRONT_HPP
#include
#include
#include
#include
#include
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template
constexpr decltype(auto) front_t::operator()(Xs&& xs) const {
using It = typename hana::tag_of::type;
using Front = BOOST_HANA_DISPATCH_IF(front_impl,
hana::Iterable::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Iterable::value,
"hana::front(xs) requires 'xs' to be an Iterable");
#endif
return Front::apply(static_cast(xs));
}
//! @endcond
template
struct front_impl> : default_ {
template
static constexpr decltype(auto) apply(Xs&& xs)
{ return hana::at_c<0>(static_cast(xs)); }
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FRONT_HPP