summaryrefslogtreecommitdiff
path: root/boost/hof/capture.hpp
blob: 8ddeb779ec2dcc5df7de6ff11fb4322d29537d27 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
/*=============================================================================
    Copyright (c) 2015 Paul Fultz II
    capture.h
    Distributed under the Boost Software License, Version 1.0. (See accompanying
    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
==============================================================================*/

#ifndef BOOST_HOF_GUARD_CAPTURE_H
#define BOOST_HOF_GUARD_CAPTURE_H

#include <boost/hof/detail/callable_base.hpp>
#include <boost/hof/detail/compressed_pair.hpp>
#include <boost/hof/reveal.hpp>
#include <boost/hof/pack.hpp>
#include <boost/hof/always.hpp>
#include <boost/hof/detail/move.hpp>
#include <boost/hof/detail/result_type.hpp>

/// capture
/// =======
/// 
/// Description
/// -----------
/// 
/// The `capture` function decorator is used to capture values in a function.
/// It provides more flexibility in capturing than the lambda capture list in
/// C++. It provides a way to do move and perfect capturing. The values
/// captured are prepended to the argument list of the function that will be
/// called.
/// 
/// Synopsis
/// --------
/// 
///     // Capture by decaying each value
///     template<class... Ts>
///     constexpr auto capture(Ts&&... xs);
/// 
///     // Capture lvalues by reference and rvalue reference by reference
///     template<class... Ts>
///     constexpr auto capture_forward(Ts&&... xs);
/// 
///     // Capture lvalues by reference and rvalues by value.
///     template<class... Ts>
///     constexpr auto capture_basic(Ts&&... xs);
/// 
/// Semantics
/// ---------
/// 
///     assert(capture(xs...)(f)(ys...) == f(xs..., ys...));
/// 
/// 
/// Example
/// -------
/// 
///     #include <boost/hof.hpp>
///     #include <cassert>
/// 
///     struct sum_f
///     {
///         template<class T, class U>
///         T operator()(T x, U y) const
///         {
///             return x+y;
///         }
///     };
/// 
///     int main() {
///         auto add_one = boost::hof::capture(1)(sum_f());
///         assert(add_one(2) == 3);
///     }
/// 

namespace boost { namespace hof {

namespace detail {

template<class F, class Pack>
struct capture_invoke : detail::compressed_pair<detail::callable_base<F>, Pack>, detail::function_result_type<F>
{
    typedef capture_invoke fit_rewritable1_tag;
    typedef detail::compressed_pair<detail::callable_base<F>, Pack> base;
    BOOST_HOF_INHERIT_CONSTRUCTOR(capture_invoke, base)
    template<class... Ts>
    constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const noexcept
    {
        return this->first(xs...);
    }

    template<class... Ts>
    constexpr const Pack& get_pack(Ts&&...xs) const noexcept
    {
        return this->second(xs...);
    }

    template<class Failure, class... Ts>
    struct unpack_capture_failure
    {
        template<class... Us>
        struct apply
        {
            typedef typename Failure::template of<Us..., Ts...> type;
        };
    };

    struct capture_failure
    {
        template<class Failure>
        struct apply
        {
            template<class... Ts>
            struct of
            : Pack::template apply<unpack_capture_failure<Failure, Ts...>>::type
            {};
        };
    };

    struct failure
    : failure_map<capture_failure, detail::callable_base<F>>
    {};

    BOOST_HOF_RETURNS_CLASS(capture_invoke);

    template<class... Ts>
    constexpr BOOST_HOF_SFINAE_RESULT
    (
        typename result_of<decltype(boost::hof::pack_join), 
            id_<const Pack&>, 
            result_of<decltype(boost::hof::pack_forward), id_<Ts>...> 
        >::type,
        id_<detail::callable_base<F>&&>
    ) 
    operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
    (
        boost::hof::pack_join
        (
            BOOST_HOF_MANGLE_CAST(const Pack&)(BOOST_HOF_CONST_THIS->get_pack(xs...)), 
            boost::hof::pack_forward(BOOST_HOF_FORWARD(Ts)(xs)...)
        )
        (BOOST_HOF_RETURNS_C_CAST(detail::callable_base<F>&&)(BOOST_HOF_CONST_THIS->base_function(xs...)))
    );
};

template<class Pack>
struct capture_pack : Pack
{
    BOOST_HOF_INHERIT_CONSTRUCTOR(capture_pack, Pack);

    BOOST_HOF_RETURNS_CLASS(capture_pack);

    // TODO: Should use rvalue ref qualifier
    template<class F>
    constexpr auto operator()(F f) const BOOST_HOF_SFINAE_RETURNS
    (
        capture_invoke<F, Pack>(BOOST_HOF_RETURNS_STATIC_CAST(F&&)(f), 
            BOOST_HOF_RETURNS_C_CAST(Pack&&)(
                BOOST_HOF_RETURNS_STATIC_CAST(const Pack&)(*boost::hof::always(BOOST_HOF_CONST_THIS)(f))
            )
        )
    );
};

struct make_capture_pack_f
{
    template<class Pack>
    constexpr capture_pack<Pack> operator()(Pack p) const
    BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(capture_pack<Pack>, Pack&&)
    {
        return capture_pack<Pack>(static_cast<Pack&&>(p));
    }
};

template<class F>
struct capture_f
{
    template<class... Ts>
    constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
    (
        BOOST_HOF_RETURNS_CONSTRUCT(make_capture_pack_f)()(BOOST_HOF_RETURNS_CONSTRUCT(F)()(BOOST_HOF_FORWARD(Ts)(xs)...))
    );
};
}

BOOST_HOF_DECLARE_STATIC_VAR(capture_basic, detail::capture_f<detail::pack_basic_f>);
BOOST_HOF_DECLARE_STATIC_VAR(capture_forward, detail::capture_f<detail::pack_forward_f>);
BOOST_HOF_DECLARE_STATIC_VAR(capture, detail::capture_f<detail::pack_f>);

}} // namespace boost::hof

#endif