1/*=============================================================================
2 Copyright (c) 2015 Paul Fultz II
3 capture.h
4 Distributed under the Boost Software License, Version 1.0. (See accompanying
5 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6==============================================================================*/
7
8#ifndef BOOST_HOF_GUARD_CAPTURE_H
9#define BOOST_HOF_GUARD_CAPTURE_H
10
11#include <boost/hof/detail/callable_base.hpp>
12#include <boost/hof/detail/compressed_pair.hpp>
13#include <boost/hof/reveal.hpp>
14#include <boost/hof/pack.hpp>
15#include <boost/hof/always.hpp>
16#include <boost/hof/detail/move.hpp>
17#include <boost/hof/detail/result_type.hpp>
18
19/// capture
20/// =======
21///
22/// Description
23/// -----------
24///
25/// The `capture` function decorator is used to capture values in a function.
26/// It provides more flexibility in capturing than the lambda capture list in
27/// C++. It provides a way to do move and perfect capturing. The values
28/// captured are prepended to the argument list of the function that will be
29/// called.
30///
31/// Synopsis
32/// --------
33///
34/// // Capture by decaying each value
35/// template<class... Ts>
36/// constexpr auto capture(Ts&&... xs);
37///
38/// // Capture lvalues by reference and rvalue reference by reference
39/// template<class... Ts>
40/// constexpr auto capture_forward(Ts&&... xs);
41///
42/// // Capture lvalues by reference and rvalues by value.
43/// template<class... Ts>
44/// constexpr auto capture_basic(Ts&&... xs);
45///
46/// Semantics
47/// ---------
48///
49/// assert(capture(xs...)(f)(ys...) == f(xs..., ys...));
50///
51///
52/// Example
53/// -------
54///
55/// #include <boost/hof.hpp>
56/// #include <cassert>
57///
58/// struct sum_f
59/// {
60/// template<class T, class U>
61/// T operator()(T x, U y) const
62/// {
63/// return x+y;
64/// }
65/// };
66///
67/// int main() {
68/// auto add_one = boost::hof::capture(1)(sum_f());
69/// assert(add_one(2) == 3);
70/// }
71///
72
73namespace boost { namespace hof {
74
75namespace detail {
76
77template<class F, class Pack>
78struct capture_invoke : detail::compressed_pair<detail::callable_base<F>, Pack>, detail::function_result_type<F>
79{
80 typedef capture_invoke fit_rewritable1_tag;
81 typedef detail::compressed_pair<detail::callable_base<F>, Pack> base;
82 BOOST_HOF_INHERIT_CONSTRUCTOR(capture_invoke, base)
83 template<class... Ts>
84 constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const noexcept
85 {
86 return this->first(xs...);
87 }
88
89 template<class... Ts>
90 constexpr const Pack& get_pack(Ts&&...xs) const noexcept
91 {
92 return this->second(xs...);
93 }
94
95 template<class Failure, class... Ts>
96 struct unpack_capture_failure
97 {
98 template<class... Us>
99 struct apply
100 {
101 typedef typename Failure::template of<Us..., Ts...> type;
102 };
103 };
104
105 struct capture_failure
106 {
107 template<class Failure>
108 struct apply
109 {
110 template<class... Ts>
111 struct of
112 : Pack::template apply<unpack_capture_failure<Failure, Ts...>>::type
113 {};
114 };
115 };
116
117 struct failure
118 : failure_map<capture_failure, detail::callable_base<F>>
119 {};
120
121 BOOST_HOF_RETURNS_CLASS(capture_invoke);
122
123 template<class... Ts>
124 constexpr BOOST_HOF_SFINAE_RESULT
125 (
126 typename result_of<decltype(boost::hof::pack_join),
127 id_<const Pack&>,
128 result_of<decltype(boost::hof::pack_forward), id_<Ts>...>
129 >::type,
130 id_<detail::callable_base<F>&&>
131 )
132 operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
133 (
134 boost::hof::pack_join
135 (
136 BOOST_HOF_MANGLE_CAST(const Pack&)(BOOST_HOF_CONST_THIS->get_pack(xs...)),
137 boost::hof::pack_forward(BOOST_HOF_FORWARD(Ts)(xs)...)
138 )
139 (BOOST_HOF_RETURNS_C_CAST(detail::callable_base<F>&&)(BOOST_HOF_CONST_THIS->base_function(xs...)))
140 );
141};
142
143template<class Pack>
144struct capture_pack : Pack
145{
146 BOOST_HOF_INHERIT_CONSTRUCTOR(capture_pack, Pack);
147
148 BOOST_HOF_RETURNS_CLASS(capture_pack);
149
150 // TODO: Should use rvalue ref qualifier
151 template<class F>
152 constexpr auto operator()(F f) const BOOST_HOF_SFINAE_RETURNS
153 (
154 capture_invoke<F, Pack>(BOOST_HOF_RETURNS_STATIC_CAST(F&&)(f),
155 BOOST_HOF_RETURNS_C_CAST(Pack&&)(
156 BOOST_HOF_RETURNS_STATIC_CAST(const Pack&)(*boost::hof::always(BOOST_HOF_CONST_THIS)(f))
157 )
158 )
159 );
160};
161
162struct make_capture_pack_f
163{
164 template<class Pack>
165 constexpr capture_pack<Pack> operator()(Pack p) const
166 BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(capture_pack<Pack>, Pack&&)
167 {
168 return capture_pack<Pack>(static_cast<Pack&&>(p));
169 }
170};
171
172template<class F>
173struct capture_f
174{
175 template<class... Ts>
176 constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
177 (
178 BOOST_HOF_RETURNS_CONSTRUCT(make_capture_pack_f)()(BOOST_HOF_RETURNS_CONSTRUCT(F)()(BOOST_HOF_FORWARD(Ts)(xs)...))
179 );
180};
181}
182
183BOOST_HOF_DECLARE_STATIC_VAR(capture_basic, detail::capture_f<detail::pack_basic_f>);
184BOOST_HOF_DECLARE_STATIC_VAR(capture_forward, detail::capture_f<detail::pack_forward_f>);
185BOOST_HOF_DECLARE_STATIC_VAR(capture, detail::capture_f<detail::pack_f>);
186
187}} // namespace boost::hof
188
189#endif
190

source code of boost/libs/hof/include/boost/hof/capture.hpp