Edit: /usr/include/boost/hana/first.hpp (1242B)
/*!
@file
Defines `boost::hana::first`.
@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_FIRST_HPP
#define BOOST_HANA_FIRST_HPP
#include
#include
#include
#include
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template
constexpr decltype(auto) first_t::operator()(Pair&& pair) const {
using P = typename hana::tag_of::type;
using First = BOOST_HANA_DISPATCH_IF(first_impl,
hana::Product
::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Product
::value,
"hana::first(pair) requires 'pair' to be a Product");
#endif
return First::apply(static_cast(pair));
}
//! @endcond
template
struct first_impl> : default_ {
template
static constexpr auto apply(Args&& ...) = delete;
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FIRST_HPP