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
|
/*!
@file
Defines `boost::hana::slice` and `boost::hana::slice_c`.
@copyright Louis Dionne 2013-2017
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_SLICE_HPP
#define BOOST_HANA_SLICE_HPP
#include <boost/hana/fwd/slice.hpp>
#include <boost/hana/at.hpp>
#include <boost/hana/concept/foldable.hpp>
#include <boost/hana/concept/sequence.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/core/make.hpp>
#include <boost/hana/range.hpp>
#include <boost/hana/unpack.hpp>
#include <cstddef>
#include <utility>
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template <typename Xs, typename Indices>
constexpr auto slice_t::operator()(Xs&& xs, Indices&& indices) const {
using S = typename hana::tag_of<Xs>::type;
using Slice = BOOST_HANA_DISPATCH_IF(slice_impl<S>,
hana::Sequence<S>::value &&
hana::Foldable<Indices>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence<S>::value,
"hana::slice(xs, indices) requires 'xs' to be a Sequence");
static_assert(hana::Foldable<Indices>::value,
"hana::slice(xs, indices) requires 'indices' to be Foldable");
#endif
return Slice::apply(static_cast<Xs&&>(xs), static_cast<Indices&&>(indices));
}
//! @endcond
namespace detail {
template <typename Xs>
struct take_arbitrary {
Xs& xs;
using S = typename hana::tag_of<Xs>::type;
template <typename ...N>
constexpr auto operator()(N const& ...) const {
return hana::make<S>(hana::at_c<N::value>(xs)...);
}
};
}
template <typename S, bool condition>
struct slice_impl<S, when<condition>> : default_ {
template <std::size_t from, typename Xs, std::size_t ...i>
static constexpr auto from_offset(Xs&& xs, std::index_sequence<i...>) {
return hana::make<S>(hana::at_c<from + i>(static_cast<Xs&&>(xs))...);
}
template <typename Xs, typename T, T from, T to>
static constexpr auto apply(Xs&& xs, hana::range<T, from, to> const&) {
return slice_impl::from_offset<from>(
static_cast<Xs&&>(xs), std::make_index_sequence<to - from>{}
);
}
//! @todo
//! Since we have the right to specify the same index more than once,
//! we can't move from the elements of the source sequence even if it
//! is a temporary object: we could end up double-moving. Perhaps it
//! would be possible to determine the indices from which we can move
//! without incurring a too large compile-time penalty?
template <typename Xs, typename Indices>
static constexpr auto apply(Xs const& xs, Indices const& indices) {
return hana::unpack(indices, detail::take_arbitrary<Xs const>{xs});
}
};
template <std::size_t from, std::size_t to>
struct slice_c_t {
template <typename Xs>
constexpr auto operator()(Xs&& xs) const {
return hana::slice(static_cast<Xs&&>(xs),
hana::range_c<std::size_t, from, to>);
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_SLICE_HPP
|
