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/*!
@file
Defines `boost::hana::is_empty`.
@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_IS_EMPTY_HPP
#define BOOST_HANA_IS_EMPTY_HPP
#include <boost/hana/fwd/is_empty.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 auto is_empty_t::operator()(Xs const& xs) const {
using It = typename hana::tag_of<Xs>::type;
using IsEmpty = BOOST_HANA_DISPATCH_IF(is_empty_impl<It>,
hana::Iterable<It>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Iterable<It>::value,
"hana::is_empty(xs) requires 'xs' to be an Iterable");
#endif
return IsEmpty::apply(xs);
}
//! @endcond
template <typename It, bool condition>
struct is_empty_impl<It, when<condition>> : default_ {
template <typename ...Args>
static constexpr auto apply(Args&& ...) = delete;
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_IS_EMPTY_HPP
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