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/*!
@file
Forward declares `boost::hana::is_empty`.
@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_FWD_IS_EMPTY_HPP
#define BOOST_HANA_FWD_IS_EMPTY_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! Returns whether the iterable is empty.
//! @ingroup group-Iterable
//!
//! Given an `Iterable` `xs`, `is_empty` returns whether `xs` contains
//! no more elements. In other words, it returns whether trying to
//! extract the tail of `xs` would be an error. In the current version
//! of the library, `is_empty` must return an `IntegralConstant` holding
//! a value convertible to `bool`. This is because only compile-time
//! `Iterable`s are supported right now.
//!
//!
//! Example
//! -------
//! @include example/is_empty.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto is_empty = [](auto const& xs) {
return tag-dispatched;
};
#else
template <typename It, typename = void>
struct is_empty_impl : is_empty_impl<It, when<true>> { };
struct is_empty_t {
template <typename Xs>
constexpr auto operator()(Xs const& xs) const;
};
constexpr is_empty_t is_empty{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FWD_IS_EMPTY_HPP
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