projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Forward declares `boost::hana::is_empty`. | |
| 4 | ||
| 5 | @copyright Louis Dionne 2013-2016 | |
| 6 | Distributed under the Boost Software License, Version 1.0. | |
| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
| 8 | */ | |
| 9 | ||
| 10 | #ifndef BOOST_HANA_FWD_IS_EMPTY_HPP | |
| 11 | #define BOOST_HANA_FWD_IS_EMPTY_HPP | |
| 12 | ||
| 13 | #include <boost/hana/config.hpp> | |
| 14 | #include <boost/hana/core/when.hpp> | |
| 15 | ||
| 16 | ||
| 17 | BOOST_HANA_NAMESPACE_BEGIN | |
| 18 | //! Returns whether the iterable is empty. | |
| 19 | //! @ingroup group-Iterable | |
| 20 | //! | |
| 21 | //! Given an `Iterable` `xs`, `is_empty` returns whether `xs` contains | |
| 22 | //! no more elements. In other words, it returns whether trying to | |
| 23 | //! extract the tail of `xs` would be an error. In the current version | |
| 24 | //! of the library, `is_empty` must return an `IntegralConstant` holding | |
| 25 | //! a value convertible to `bool`. This is because only compile-time | |
| 26 | //! `Iterable`s are supported right now. | |
| 27 | //! | |
| 28 | //! | |
| 29 | //! Example | |
| 30 | //! ------- | |
| 31 | //! @include example/is_empty.cpp | |
| 32 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
| 33 | constexpr auto is_empty = [](auto const& xs) { | |
| 34 | return tag-dispatched; | |
| 35 | }; | |
| 36 | #else | |
| 37 | template <typename It, typename = void> | |
| 38 | struct is_empty_impl : is_empty_impl<It, when<true>> { }; | |
| 39 | ||
| 40 | struct is_empty_t { | |
| 41 | template <typename Xs> | |
| 42 | constexpr auto operator()(Xs const& xs) const; | |
| 43 | }; | |
| 44 | ||
| 45 | constexpr is_empty_t is_empty{}; | |
| 46 | #endif | |
| 47 | BOOST_HANA_NAMESPACE_END | |
| 48 | ||
| 49 | #endif // !BOOST_HANA_FWD_IS_EMPTY_HPP |