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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::reverse_partial`. | |
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_FUNCTIONAL_REVERSE_PARTIAL_HPP | |
11 | #define BOOST_HANA_FUNCTIONAL_REVERSE_PARTIAL_HPP | |
12 | ||
13 | #include <boost/hana/basic_tuple.hpp> | |
14 | #include <boost/hana/config.hpp> | |
15 | #include <boost/hana/detail/decay.hpp> | |
16 | ||
17 | #include <cstddef> | |
18 | #include <utility> | |
19 | ||
20 | ||
21 | BOOST_HANA_NAMESPACE_BEGIN | |
22 | //! @ingroup group-functional | |
23 | //! Partially apply a function to some arguments. | |
24 | //! | |
25 | //! Given a function `f` and some arguments, `reverse_partial` returns a | |
26 | //! new function corresponding to `f` whose last arguments are partially | |
27 | //! applied. Specifically, `reverse_partial(f, x...)` is a function such | |
28 | //! that | |
29 | //! @code | |
30 | //! reverse_partial(f, x...)(y...) == f(y..., x...) | |
31 | //! @endcode | |
32 | //! | |
33 | //! @note | |
34 | //! The arity of `f` must match the total number of arguments passed to | |
35 | //! it, i.e. `sizeof...(x) + sizeof...(y)`. | |
36 | //! | |
37 | //! | |
38 | //! Example | |
39 | //! ------- | |
40 | //! @include example/functional/reverse_partial.cpp | |
41 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
42 | constexpr auto reverse_partial = [](auto&& f, auto&& ...x) { | |
43 | return [perfect-capture](auto&& ...y) -> decltype(auto) { | |
44 | return forwarded(f)(forwarded(y)..., forwarded(x)...); | |
45 | }; | |
46 | }; | |
47 | #else | |
48 | template <typename Indices, typename F, typename ...X> | |
49 | struct reverse_partial_t; | |
50 | ||
51 | struct make_reverse_partial_t { | |
52 | struct secret { }; | |
53 | template <typename F, typename ...X> | |
54 | constexpr reverse_partial_t< | |
55 | std::make_index_sequence<sizeof...(X)>, | |
56 | typename detail::decay<F>::type, | |
57 | typename detail::decay<X>::type... | |
58 | > operator()(F&& f, X&& ...x) const { | |
59 | return {secret{}, static_cast<F&&>(f), static_cast<X&&>(x)...}; | |
60 | } | |
61 | }; | |
62 | ||
63 | template <std::size_t ...n, typename F, typename ...X> | |
64 | struct reverse_partial_t<std::index_sequence<n...>, F, X...> { | |
65 | reverse_partial_t() = default; | |
66 | ||
67 | template <typename ...T> | |
68 | constexpr reverse_partial_t(make_reverse_partial_t::secret, T&& ...t) | |
69 | : storage_{static_cast<T&&>(t)...} | |
70 | { } | |
71 | ||
72 | basic_tuple<F, X...> storage_; | |
73 | ||
74 | template <typename ...Y> | |
75 | constexpr decltype(auto) operator()(Y&& ...y) const& { | |
76 | return hana::get_impl<0>(storage_)( | |
77 | static_cast<Y&&>(y)..., | |
78 | hana::get_impl<n+1>(storage_)... | |
79 | ); | |
80 | } | |
81 | ||
82 | template <typename ...Y> | |
83 | constexpr decltype(auto) operator()(Y&& ...y) & { | |
84 | return hana::get_impl<0>(storage_)( | |
85 | static_cast<Y&&>(y)..., | |
86 | hana::get_impl<n+1>(storage_)... | |
87 | ); | |
88 | } | |
89 | ||
90 | template <typename ...Y> | |
91 | constexpr decltype(auto) operator()(Y&& ...y) && { | |
92 | return static_cast<F&&>(hana::get_impl<0>(storage_))( | |
93 | static_cast<Y&&>(y)..., | |
94 | static_cast<X&&>(hana::get_impl<n+1>(storage_))... | |
95 | ); | |
96 | } | |
97 | }; | |
98 | ||
99 | constexpr make_reverse_partial_t reverse_partial{}; | |
100 | #endif | |
101 | BOOST_HANA_NAMESPACE_END | |
102 | ||
103 | #endif // !BOOST_HANA_FUNCTIONAL_REVERSE_PARTIAL_HPP |