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
|
/*!
@file
Defines `boost::hana::drop_front_exactly`.
@copyright Louis Dionne 2013-2016
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_DROP_FRONT_EXACTLY_HPP
#define BOOST_HANA_DROP_FRONT_EXACTLY_HPP
#include <boost/hana/fwd/drop_front_exactly.hpp>
#include <boost/hana/bool.hpp>
#include <boost/hana/concept/integral_constant.hpp>
#include <boost/hana/concept/iterable.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/drop_front.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/is_empty.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template <typename Xs, typename N>
constexpr auto drop_front_exactly_t::operator()(Xs&& xs, N const& n) const {
using It = typename hana::tag_of<Xs>::type;
using DropFrontExactly = BOOST_HANA_DISPATCH_IF(drop_front_exactly_impl<It>,
hana::Iterable<It>::value &&
hana::IntegralConstant<N>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Iterable<It>::value,
"hana::drop_front_exactly(xs, n) requires 'xs' to be an Iterable");
static_assert(hana::IntegralConstant<N>::value,
"hana::drop_front_exactly(xs, n) requires 'n' to be an IntegralConstant");
#endif
static_assert(N::value >= 0,
"hana::drop_front_exactly(xs, n) requires 'n' to be non-negative");
return DropFrontExactly::apply(static_cast<Xs&&>(xs), n);
}
template <typename Xs>
constexpr auto drop_front_exactly_t::operator()(Xs&& xs) const {
return (*this)(static_cast<Xs&&>(xs), hana::size_c<1>);
}
//! @endcond
namespace detail {
template <typename Xs, typename N>
constexpr void check_dfe_overflow(Xs const& xs, N const&, hana::true_) {
constexpr bool n_overflew_length = decltype(
hana::is_empty(hana::drop_front(xs, hana::size_c<N::value - 1>))
)::value;
static_assert(!n_overflew_length,
"hana::drop_front_exactly(xs, n) requires 'n' to be less than or "
"equal to the number of elements in 'xs'");
}
template <typename Xs, typename N>
constexpr void check_dfe_overflow(Xs const&, N const&, hana::false_) { }
}
template <typename It, bool condition>
struct drop_front_exactly_impl<It, when<condition>> : default_ {
template <typename Xs, typename N>
static constexpr auto apply(Xs&& xs, N const& n) {
auto result = hana::drop_front(static_cast<Xs&&>(xs), n);
constexpr bool check_for_overflow =
decltype(hana::is_empty(result))::value && N::value != 0;
detail::check_dfe_overflow(xs, n, hana::bool_c<check_for_overflow>);
return result; // NRVO applied
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_DROP_FRONT_EXACTLY_HPP
|
