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1 /*!
2 @file
3 Forward declares `boost::hana::or_`.
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_OR_HPP
11 #define BOOST_HANA_FWD_OR_HPP
12
13 #include <boost/hana/config.hpp>
14 #include <boost/hana/core/when.hpp>
15
16
17 BOOST_HANA_NAMESPACE_BEGIN
18 //! Return whether any of the arguments is true-valued.
19 //! @ingroup group-Logical
20 //!
21 //! `or_` can be called with one argument or more. When called with
22 //! two arguments, `or_` uses tag-dispatching to find the right
23 //! implementation. Otherwise,
24 //! @code
25 //! or_(x) == x
26 //! or_(x, y, ...z) == or_(or_(x, y), z...)
27 //! @endcode
28 //!
29 //!
30 //! Example
31 //! -------
32 //! @include example/or.cpp
33 #ifdef BOOST_HANA_DOXYGEN_INVOKED
34 constexpr auto or_ = [](auto&& x, auto&& ...y) -> decltype(auto) {
35 return tag-dispatched;
36 };
37 #else
38 template <typename L, typename = void>
39 struct or_impl : or_impl<L, when<true>> { };
40
41 struct or_t {
42 template <typename X, typename Y>
43 constexpr decltype(auto) operator()(X&& x, Y&& y) const;
44
45 template <typename X, typename ...Y>
46 constexpr decltype(auto) operator()(X&& x, Y&& ...y) const;
47 };
48
49 constexpr or_t or_{};
50 #endif
51 BOOST_HANA_NAMESPACE_END
52
53 #endif // !BOOST_HANA_FWD_OR_HPP