OpenTTD Source  12.0-beta2
span_type.hpp
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1 /*
2  * This file is part of OpenTTD.
3  * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
4  * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
5  * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
6  */
7 
10 #ifndef CORE_SPAN_TYPE_HPP
11 #define CORE_SPAN_TYPE_HPP
12 
13 /* This is a partial copy/paste from https://github.com/gsl-lite/gsl-lite/blob/master/include/gsl/gsl-lite.hpp */
14 
15 /* Template to check if a template variable defines size() and data(). */
16 template <class, class = void>
17 struct has_size_and_data : std::false_type{};
18 template <class C>
20 <
21  C, std::void_t<
22  decltype(std::size(std::declval<C>())),
23  decltype(std::data(std::declval<C>()))>
24 > : std::true_type{};
25 
26 /* Template to check if two elements are compatible. */
27 template <class, class, class = void>
28 struct is_compatible_element : std::false_type {};
29 template <class C, class E>
31 <
32  C, E, std::void_t<
33  decltype(std::data(std::declval<C>())),
34  typename std::remove_pointer<decltype(std::data( std::declval<C&>()))>::type(*)[]>
35 > : std::is_convertible<typename std::remove_pointer<decltype(std::data(std::declval<C&>()))>::type(*)[], E(*)[]>{};
36 
37 /* Template to check if a container is compatible. gsl-lite also includes is_array and is_std_array, but as we don't use them, they are omitted. */
38 template <class C, class E>
39 struct is_compatible_container : std::bool_constant
40 <
41  has_size_and_data<C>::value
42  && is_compatible_element<C,E>::value
43 >{};
44 
59 template<class T>
60 class span {
61 public:
62  typedef T element_type;
63  typedef typename std::remove_cv< T >::type value_type;
64 
65  typedef T &reference;
66  typedef T *pointer;
67  typedef const T &const_reference;
68  typedef const T *const_pointer;
69 
70  typedef pointer iterator;
71  typedef const_pointer const_iterator;
72 
73  typedef size_t size_type;
74  typedef std::ptrdiff_t difference_type;
75 
76  constexpr span() noexcept : first(nullptr), last(nullptr) {}
77 
78  constexpr span(pointer data_in, size_t size_in) : first(data_in), last(data_in + size_in) {}
79 
80  template<class Container, typename std::enable_if<(is_compatible_container<Container, element_type>::value), int>::type = 0>
81  constexpr span(Container &list) noexcept : first(std::data(list)), last(std::data(list) + std::size(list)) {}
82  template<class Container, typename std::enable_if<(std::is_const<element_type>::value && is_compatible_container<Container, element_type>::value), int>::type = 0>
83  constexpr span(const Container &list) noexcept : first(std::data(list)), last(std::data(list) + std::size(list)) {}
84 
85  constexpr size_t size() const noexcept { return static_cast<size_t>( last - first ); }
86  constexpr std::ptrdiff_t ssize() const noexcept { return static_cast<std::ptrdiff_t>( last - first ); }
87  constexpr bool empty() const noexcept { return size() == 0; }
88 
89  constexpr iterator begin() const noexcept { return iterator(first); }
90  constexpr iterator end() const noexcept { return iterator(last); }
91 
92  constexpr const_iterator cbegin() const noexcept { return const_iterator(first); }
93  constexpr const_iterator cend() const noexcept { return const_iterator(last); }
94 
95 private:
96  pointer first;
97  pointer last;
98 };
99 
100 #endif /* CORE_SPAN_TYPE_HPP */
has_size_and_data
Definition: span_type.hpp:17
is_compatible_container
Definition: span_type.hpp:39
is_compatible_element
Definition: span_type.hpp:28
span
A trimmed down version of what std::span will be in C++20.
Definition: span_type.hpp:60