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
|
/*!
@file
Forward declares `boost::hana::sort`.
@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_FWD_SORT_HPP
#define BOOST_HANA_FWD_SORT_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
#include <boost/hana/detail/nested_by_fwd.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! Sort a sequence, optionally based on a custom `predicate`.
//! @ingroup group-Sequence
//!
//! Given a Sequence and an optional predicate (by default `less`), `sort`
//! returns a new sequence containing the same elements as the original,
//! except they are ordered in such a way that if `x` comes before `y` in
//! the sequence, then either `predicate(x, y)` is true, or both
//! `predicate(x, y)` and `predicate(y, x)` are false.
//!
//! Also note that the sort is guaranteed to be stable. Hence, if `x`
//! comes before `y` in the original sequence and both `predicate(x, y)`
//! and `predicate(y, x)` are false, then `x` will come before `y` in the
//! resulting sequence.
//!
//! If no predicate is provided, the elements in the sequence must all be
//! compile-time `Orderable`.
//!
//! Signature
//! ---------
//! Given a `Sequence` `S(T)`, a boolean `IntegralConstant` `Bool` and a
//! binary predicate \f$ T \times T \to Bool \f$, `sort` has the following
//! signatures. For the variant with a provided predicate,
//! \f[
//! \mathtt{sort} : S(T) \times (T \times T \to Bool) \to S(T)
//! \f]
//!
//! for the variant without a custom predicate, `T` is required to be
//! `Orderable`. The signature is then
//! \f[
//! \mathtt{sort} : S(T) \to S(T)
//! \f]
//!
//! @param xs
//! The sequence to sort.
//!
//! @param predicate
//! A function called as `predicate(x, y)` for two elements `x` and `y` of
//! the sequence, and returning a boolean `IntegralConstant` representing
//! whether `x` is to be considered _less_ than `y`, i.e. whether `x` should
//! appear _before_ `y` in the resulting sequence. More specifically,
//! `predicate` must define a [strict weak ordering][1] on the elements
//! of the sequence. When the predicate is not specified, this defaults
//! to `less`. In the current version of the library, the predicate has
//! to return an `IntegralConstant` holding a value convertible to a `bool`.
//!
//!
//! Syntactic sugar (`sort.by`)
//! ---------------------------
//! `sort` can be called in a third way, which provides a nice syntax
//! especially when working with the `ordering` combinator:
//! @code
//! sort.by(predicate, xs) == sort(xs, predicate)
//! sort.by(predicate) == sort(-, predicate)
//! @endcode
//!
//! where `sort(-, predicate)` denotes the partial application of
//! `sort` to `predicate`.
//!
//!
//! Example
//! -------
//! @include example/sort.cpp
//!
//! Benchmarks
//! ----------
//! <div class="benchmark-chart"
//! style="min-width: 310px; height: 400px; margin: 0 auto"
//! data-dataset="benchmark.sort.compile.json">
//! </div>
//!
//! [1]: http://en.wikipedia.org/wiki/Strict_weak_ordering
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto sort = [](auto&& xs[, auto&& predicate]) {
return tag-dispatched;
};
#else
template <typename S, typename = void>
struct sort_impl : sort_impl<S, when<true>> { };
struct sort_t : detail::nested_by<sort_t> {
template <typename Xs>
constexpr auto operator()(Xs&& xs) const;
template <typename Xs, typename Predicate>
constexpr auto operator()(Xs&& xs, Predicate&& pred) const;
};
constexpr sort_t sort{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FWD_SORT_HPP
|
