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1 | /*! |
2 | @file | |
3 | Forward declares `boost::hana::range`. | |
4 | ||
5 | @copyright Louis Dionne 2013-2016 | |
6 | Distributed under the Boost Software License, Version 1.0. | |
7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
8 | */ | |
9 | ||
10 | #ifndef BOOST_HANA_FWD_RANGE_HPP | |
11 | #define BOOST_HANA_FWD_RANGE_HPP | |
12 | ||
13 | #include <boost/hana/config.hpp> | |
14 | #include <boost/hana/fwd/core/make.hpp> | |
15 | #include <boost/hana/fwd/integral_constant.hpp> | |
16 | ||
17 | ||
18 | BOOST_HANA_NAMESPACE_BEGIN | |
19 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
20 | //! @ingroup group-datatypes | |
21 | //! Compile-time half-open interval of `hana::integral_constant`s. | |
22 | //! | |
23 | //! A `range` represents a half-open interval of the form `[from, to)` | |
24 | //! containing `hana::integral_constant`s of a given type. The `[from, to)` | |
25 | //! notation represents the values starting at `from` (inclusively) up | |
26 | //! to but excluding `from`. In other words, it is a bit like the list | |
27 | //! `from, from+1, ..., to-1`. | |
28 | //! | |
29 | //! In particular, note that the bounds of the range can be any | |
30 | //! `hana::integral_constant`s (negative numbers are allowed) and the | |
31 | //! range does not have to start at zero. The only requirement is that | |
32 | //! `from <= to`. | |
33 | //! | |
34 | //! @note | |
35 | //! The representation of `hana::range` is implementation defined. In | |
36 | //! particular, one should not take for granted the number and types | |
37 | //! of template parameters. The proper way to create a `hana::range` | |
38 | //! is to use `hana::range_c` or `hana::make_range`. | |
39 | //! | |
40 | //! | |
41 | //! Modeled concepts | |
42 | //! ---------------- | |
43 | //! 1. `Comparable`\n | |
44 | //! Two ranges are equal if and only if they are both empty or they both | |
45 | //! span the same interval. | |
46 | //! @include example/range/comparable.cpp | |
47 | //! | |
48 | //! 2. `Foldable`\n | |
49 | //! Folding a `range` is equivalent to folding a list of the | |
50 | //! `integral_constant`s in the interval it spans. | |
51 | //! @include example/range/foldable.cpp | |
52 | //! | |
53 | //! 3. `Iterable`\n | |
54 | //! Iterating over a `range` is equivalent to iterating over a list of | |
55 | //! the values it spans. In other words, iterating over the range | |
56 | //! `[from, to)` is equivalent to iterating over a list containing | |
57 | //! `from, from+1, from+2, ..., to-1`. Also note that `operator[]` can | |
58 | //! be used in place of the `at` function. | |
59 | //! @include example/range/iterable.cpp | |
60 | //! | |
61 | //! 4. `Searchable`\n | |
62 | //! Searching a `range` is equivalent to searching a list of the values | |
63 | //! in the range `[from, to)`, but it is much more compile-time efficient. | |
64 | //! @include example/range/searchable.cpp | |
65 | template <typename T, T from, T to> | |
66 | struct range { | |
67 | //! Equivalent to `hana::equal` | |
68 | template <typename X, typename Y> | |
69 | friend constexpr auto operator==(X&& x, Y&& y); | |
70 | ||
71 | //! Equivalent to `hana::not_equal` | |
72 | template <typename X, typename Y> | |
73 | friend constexpr auto operator!=(X&& x, Y&& y); | |
74 | ||
75 | //! Equivalent to `hana::at` | |
76 | template <typename N> | |
77 | constexpr decltype(auto) operator[](N&& n); | |
78 | }; | |
79 | #else | |
80 | template <typename T, T from, T to> | |
81 | struct range; | |
82 | #endif | |
83 | ||
84 | //! Tag representing a `hana::range`. | |
85 | //! @relates hana::range | |
86 | struct range_tag { }; | |
87 | ||
88 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
89 | //! Create a `hana::range` representing a half-open interval of | |
90 | //! `integral_constant`s. | |
91 | //! @relates hana::range | |
92 | //! | |
93 | //! Given two `IntegralConstant`s `from` and `to`, `make<range_tag>` | |
94 | //! returns a `hana::range` representing the half-open interval of | |
95 | //! `integral_constant`s `[from, to)`. `from` and `to` must form a | |
96 | //! valid interval, which means that `from <= to` must be true. Otherwise, | |
97 | //! a compilation error is triggered. Also note that if `from` and `to` | |
98 | //! are `IntegralConstant`s with different underlying integral types, | |
99 | //! the created range contains `integral_constant`s whose underlying | |
100 | //! type is their common type. | |
101 | //! | |
102 | //! | |
103 | //! Example | |
104 | //! ------- | |
105 | //! @include example/range/make.cpp | |
106 | template <> | |
107 | constexpr auto make<range_tag> = [](auto const& from, auto const& to) { | |
108 | return range<implementation_defined>{implementation_defined}; | |
109 | }; | |
110 | #endif | |
111 | ||
112 | //! Alias to `make<range_tag>`; provided for convenience. | |
113 | //! @relates hana::range | |
114 | constexpr auto make_range = make<range_tag>; | |
115 | ||
116 | //! Shorthand to create a `hana::range` with the given bounds. | |
117 | //! @relates hana::range | |
118 | //! | |
119 | //! This shorthand is provided for convenience only and it is equivalent | |
120 | //! to `make_range`. Specifically, `range_c<T, from, to>` is such that | |
121 | //! @code | |
122 | //! range_c<T, from, to> == make_range(integral_c<T, from>, integral_c<T, to>) | |
123 | //! @endcode | |
124 | //! | |
125 | //! | |
126 | //! @tparam T | |
127 | //! The underlying integral type of the `integral_constant`s in the | |
128 | //! created range. | |
129 | //! | |
130 | //! @tparam from | |
131 | //! The inclusive lower bound of the created range. | |
132 | //! | |
133 | //! @tparam to | |
134 | //! The exclusive upper bound of the created range. | |
135 | //! | |
136 | //! | |
137 | //! Example | |
138 | //! ------- | |
139 | //! @include example/range/range_c.cpp | |
140 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
141 | template <typename T, T from, T to> | |
142 | constexpr auto range_c = make_range(integral_c<T, from>, integral_c<T, to>); | |
143 | #else | |
144 | template <typename T, T from, T to> | |
145 | constexpr range<T, from, to> range_c{}; | |
146 | #endif | |
147 | BOOST_HANA_NAMESPACE_END | |
148 | ||
149 | #endif // !BOOST_HANA_FWD_RANGE_HPP |