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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