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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::capture`. | |
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_CAPTURE_HPP | |
11 | #define BOOST_HANA_FUNCTIONAL_CAPTURE_HPP | |
12 | ||
13 | #include <boost/hana/basic_tuple.hpp> | |
14 | #include <boost/hana/config.hpp> | |
15 | #include <boost/hana/detail/decay.hpp> | |
16 | #include <boost/hana/functional/partial.hpp> | |
17 | ||
18 | #include <cstddef> | |
19 | #include <utility> | |
20 | ||
21 | ||
22 | BOOST_HANA_NAMESPACE_BEGIN | |
23 | //! @ingroup group-functional | |
24 | //! Create a function capturing the given variables. | |
25 | //! | |
26 | //! Given 0 or more variables, `capture` creates a closure that can be | |
27 | //! used to partially apply a function. This is very similar to `partial`, | |
28 | //! except that `capture` allows the partially applied function to be | |
29 | //! specified later. Specifically, `capture(vars...)` is a function object | |
30 | //! taking a function `f` and returning `f` partially applied to `vars...`. | |
31 | //! In other words, | |
32 | //! @code | |
33 | //! capture(vars...)(f)(args...) == f(vars..., args...) | |
34 | //! @endcode | |
35 | //! | |
36 | //! @note | |
37 | //! The arity of `f` must match the total number of arguments passed to | |
38 | //! it, i.e. `sizeof...(vars) + sizeof...(args)`. | |
39 | //! | |
40 | //! | |
41 | //! Example | |
42 | //! ------- | |
43 | //! @include example/functional/capture.cpp | |
44 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
45 | constexpr auto capture = [](auto&& ...variables) { | |
46 | return [perfect-capture](auto&& f) { | |
47 | return [perfect-capture](auto&& ...args) -> decltype(auto) { | |
48 | return forwarded(f)(forwarded(variables)..., forwarded(args)...); | |
49 | }; | |
50 | }; | |
51 | }; | |
52 | #else | |
53 | namespace detail { | |
54 | template <typename F, typename Closure, std::size_t ...i> | |
55 | constexpr auto apply_capture(F&& f, Closure&& closure, std::index_sequence<i...>) { | |
56 | return hana::partial(static_cast<F&&>(f), | |
57 | hana::get_impl<i>(static_cast<Closure&&>(closure).storage_)... | |
58 | ); | |
59 | } | |
60 | } | |
61 | ||
62 | template <typename ...X> | |
63 | struct capture_t; | |
64 | ||
65 | struct make_capture_t { | |
66 | struct secret { }; | |
67 | template <typename ...X> | |
68 | constexpr capture_t<typename detail::decay<X>::type...> | |
69 | operator()(X&& ...x) const { | |
70 | return {secret{}, static_cast<X&&>(x)...}; | |
71 | } | |
72 | }; | |
73 | ||
74 | template <typename ...X> | |
75 | struct capture_t { | |
76 | template <typename ...Y> | |
77 | constexpr capture_t(make_capture_t::secret, Y&& ...y) | |
78 | : storage_{static_cast<Y&&>(y)...} | |
79 | { } | |
80 | ||
81 | basic_tuple<X...> storage_; | |
82 | ||
83 | template <typename F> | |
84 | constexpr auto operator()(F&& f) const& { | |
85 | return detail::apply_capture( | |
86 | static_cast<F&&>(f), *this, | |
87 | std::make_index_sequence<sizeof...(X)>{} | |
88 | ); | |
89 | } | |
90 | ||
91 | template <typename F> | |
92 | constexpr auto operator()(F&& f) & { | |
93 | return detail::apply_capture( | |
94 | static_cast<F&&>(f), *this, | |
95 | std::make_index_sequence<sizeof...(X)>{} | |
96 | ); | |
97 | } | |
98 | ||
99 | template <typename F> | |
100 | constexpr auto operator()(F&& f) && { | |
101 | return detail::apply_capture( | |
102 | static_cast<F&&>(f), static_cast<capture_t&&>(*this), | |
103 | std::make_index_sequence<sizeof...(X)>{} | |
104 | ); | |
105 | } | |
106 | }; | |
107 | ||
108 | constexpr make_capture_t capture{}; | |
109 | #endif | |
110 | BOOST_HANA_NAMESPACE_END | |
111 | ||
112 | #endif // !BOOST_HANA_FUNCTIONAL_CAPTURE_HPP |