]>
Commit | Line | Data |
---|---|---|
7c673cae FG |
1 | /*! |
2 | @file | |
3 | Forward declares `boost::hana::detail::nested_by`. | |
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_DETAIL_NESTED_BY_FWD_HPP | |
11 | #define BOOST_HANA_DETAIL_NESTED_BY_FWD_HPP | |
12 | ||
13 | #include <boost/hana/config.hpp> | |
14 | ||
15 | ||
16 | BOOST_HANA_NAMESPACE_BEGIN namespace detail { | |
17 | template <typename Algorithm> | |
18 | struct nested_by_t { | |
19 | template <typename Predicate, typename Object> | |
20 | constexpr decltype(auto) | |
21 | operator()(Predicate&& predicate, Object&& object) const; | |
22 | ||
23 | template <typename Predicate> | |
24 | constexpr decltype(auto) operator()(Predicate&& predicate) const; | |
25 | }; | |
26 | ||
27 | //! @ingroup group-details | |
28 | //! Provides a `.by` static constexpr function object. | |
29 | //! | |
30 | //! When creating a binary function object of type `Algorithm` whose | |
31 | //! signature is `Object x Predicate -> Return`, `nested_by<Algorithm>` | |
32 | //! can be used as a base class to `Algorithm`. Doing so will provide a | |
33 | //! static constexpr member called `by`, which has the two following | |
34 | //! signatures: | |
35 | //! @code | |
36 | //! Predicate x Object -> Return | |
37 | //! Predicate -> (Object -> Return) | |
38 | //! @endcode | |
39 | //! | |
40 | //! In other words, `nested_by` is a `curry`ed and `flip`ped version of | |
41 | //! `Algorithm`. Note that the function object `Algorithm` must be | |
42 | //! default-constructible, since the algorithm will be called as | |
43 | //! `Algorithm{}(arguments...)`. | |
44 | //! | |
45 | //! @note | |
46 | //! This function object is especially useful because it takes care of | |
47 | //! avoiding ODR violations caused by the nested static constexpr member. | |
48 | template <typename Algorithm> | |
49 | struct nested_by { static constexpr nested_by_t<Algorithm> by{}; }; | |
50 | ||
51 | template <typename Algorithm> | |
52 | constexpr nested_by_t<Algorithm> nested_by<Algorithm>::by; | |
53 | } BOOST_HANA_NAMESPACE_END | |
54 | ||
55 | #endif // !BOOST_HANA_DETAIL_NESTED_BY_FWD_HPP |