1// Copyright 2020 The Pigweed Authors
2//
3// Licensed under the Apache License, Version 2.0 (the "License"); you may not
4// use this file except in compliance with the License. You may obtain a copy of
5// the License at
6//
7//     https://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12// License for the specific language governing permissions and limitations under
13// the License.
14#pragma once
15
16#include <algorithm>
17#include <cstddef>
18#include <iterator>
19
20#include "pw_polyfill/standard_library/namespace.h"
21
22#define __cpp_lib_string_view 201606L
23
24_PW_POLYFILL_BEGIN_NAMESPACE_STD
25
26template <typename T>
27class basic_string_view {
28 public:
29  using traits_type = void;  // No traits object is used.
30  using value_type = T;
31  using pointer = T*;
32  using const_pointer = const T*;
33  using reference = T&;
34  using const_reference = const T&;
35  using const_iterator = const T*;
36  using iterator = const_iterator;
37  using const_reverse_iterator = ::std::reverse_iterator<const_iterator>;
38  using reverse_iterator = const_reverse_iterator;
39  using size_type = size_t;
40  using difference_type = ptrdiff_t;
41
42  static constexpr size_type npos = size_type(-1);
43
44  constexpr basic_string_view() noexcept : string_(nullptr), size_(0) {}
45  constexpr basic_string_view(const basic_string_view&) noexcept = default;
46  constexpr basic_string_view(const T* string, size_type count)
47      : string_(string), size_(count) {}
48  constexpr basic_string_view(const T* string)
49      : string_(string), size_(CStringLength(string)) {}
50
51  constexpr basic_string_view& operator=(const basic_string_view&) noexcept =
52      default;
53
54  constexpr const_iterator begin() const noexcept { return string_; }
55  constexpr const_iterator cbegin() const noexcept { return begin(); }
56
57  constexpr const_iterator end() const noexcept { return string_ + size_; }
58  constexpr const_iterator cend() const noexcept { return end(); }
59
60  // NOT IMPLEMENTED: Reverse iterators not supported.
61  constexpr const_reverse_iterator rbegin() const noexcept;
62  constexpr const_reverse_iterator crbegin() const noexcept;
63
64  constexpr const_reverse_iterator rend() const noexcept;
65  constexpr const_reverse_iterator crend() const noexcept;
66
67  constexpr const_reference operator[](size_type pos) const {
68    return data()[pos];
69  }
70
71  // NOT IMPLEMENTED: at() has no bounds checking.
72  constexpr const_reference at(size_type pos) const { return data()[pos]; }
73
74  constexpr const_reference front() const { return data()[0]; }
75
76  constexpr const_reference back() const { return data()[size() - 1]; }
77
78  constexpr const_pointer data() const noexcept { return string_; }
79
80  constexpr size_type size() const noexcept { return size_; }
81  constexpr size_type length() const noexcept { return size(); }
82
83  constexpr size_type max_size() const noexcept { return ~size_t{0}; }
84
85  [[nodiscard]] constexpr bool empty() const noexcept { return size() == 0u; }
86
87  constexpr void remove_prefix(size_type characters) {
88    string_ += characters;
89    size_ -= characters;
90  }
91
92  constexpr void remove_suffix(size_type characters) { size_ -= characters; }
93
94  constexpr void swap(basic_string_view& other) noexcept {
95    pointer temp_string = string_;
96    string_ = other.string_;
97    other.string_ = temp_string;
98
99    size_type temp_size = size_;
100    size_ = other.size_;
101    other.size_ = temp_size;
102  }
103
104  // NOT IMPLEMENTED: copy does no bounds checking.
105  constexpr size_type copy(T* dest, size_type count, size_type pos = 0) const {
106    const size_type to_copy = min(count, size() - pos);
107    for (size_type i = pos; i < pos + to_copy; ++i) {
108      *dest++ = string_[i];
109    }
110    return to_copy;
111  }
112
113  constexpr basic_string_view substr(size_type pos = 0,
114                                     size_type count = npos) const {
115    return basic_string_view(string_ + pos, min(count, size() - pos));
116  }
117
118  // NOT IMPLEMENTED: These functions and their overloads are not defined.
119  constexpr int compare(basic_string_view view) const noexcept;
120  constexpr bool starts_with(basic_string_view view) const noexcept;
121  constexpr bool ends_with(basic_string_view view) const noexcept;
122  constexpr size_type find(basic_string_view view,
123                           size_type pos = 0) const noexcept;
124  constexpr size_type rfind(basic_string_view view,
125                            size_type pos = npos) const noexcept;
126  constexpr size_type find_first_of(basic_string_view view,
127                                    size_type pos = 0) const noexcept;
128  constexpr size_type find_last_of(basic_string_view view,
129                                   size_type pos = npos) const noexcept;
130  constexpr size_type find_first_not_of(basic_string_view view,
131                                        size_type pos = 0) const noexcept;
132  constexpr size_type find_last_not_of(basic_string_view view,
133                                       size_type pos = npos) const noexcept;
134
135 private:
136  static constexpr size_type CStringLength(const T* string) {
137    size_type length = 0;
138    while (string[length] != T()) {
139      length += 1;
140    }
141    return length;
142  }
143
144  const_pointer string_;
145  size_type size_;
146};
147
148template <typename T>
149constexpr bool operator==(basic_string_view<T> lhs, basic_string_view<T> rhs) {
150  if (lhs.size() != rhs.size()) {
151    return false;
152  }
153  for (typename basic_string_view<T>::size_type i = 0; i < lhs.size(); ++i) {
154    if (lhs[i] != rhs[i]) {
155      return false;
156    }
157  }
158  return true;
159}
160
161template <typename T>
162constexpr bool operator!=(basic_string_view<T> lhs, basic_string_view<T> rhs) {
163  return !(lhs == rhs);
164}
165
166// NOT IMPLEMENTED: Other comparison operators are not defined.
167
168using string_view = basic_string_view<char>;
169using wstring_view = basic_string_view<wchar_t>;
170using u16string_view = basic_string_view<char16_t>;
171using u32string_view = basic_string_view<char32_t>;
172
173// NOT IMPLEMENTED: string_view literals cannot be implemented since they do not
174//                  start with _.
175
176_PW_POLYFILL_END_NAMESPACE_STD
177