cpp-common/bt2c: add CStringView equality and non-equality operators
[babeltrace.git] / src / cpp-common / bt2c / c-string-view.hpp
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1/*
2 * Copyright (c) 2023 Philippe Proulx <pproulx@efficios.com>
3 *
4 * SPDX-License-Identifier: MIT
5 */
6
7#ifndef BABELTRACE_CPP_COMMON_BT2C_C_STRING_VIEW_HPP
8#define BABELTRACE_CPP_COMMON_BT2C_C_STRING_VIEW_HPP
9
10#include <cstddef>
11#include <cstring>
12#include <string>
13
14#include "common/assert.h"
15#include "cpp-common/bt2s/string-view.hpp"
e64addc7 16#include "cpp-common/vendor/fmt/format.h"
339e8bc4 17
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18#include "type-traits.hpp"
19
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20namespace bt2c {
21
22/*
23 * A view on a constant null-terminated C string.
24 *
25 * Similar to `bt2s::string_view`, but len() and end() compute the
26 * length on demand.
27 */
28class CStringView final
29{
30public:
31 /*
32 * Builds an empty view (data() returns `nullptr`).
33 *
34 * Intentionally not explicit.
35 */
26d1608e 36 constexpr CStringView() noexcept = default;
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37
38 /*
39 * Builds a view of the C string `str` (may be `nullptr`).
40 *
41 * Intentionally not explicit.
42 */
26d1608e 43 constexpr CStringView(const char * const str) noexcept : _mStr {str}
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44 {
45 }
46
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47 /*
48 * Builds a view of the string `str`.
49 *
50 * Intentionally not explicit.
51 */
52 CStringView(const std::string& str) noexcept : _mStr {str.c_str()}
53 {
54 }
55
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56 /*
57 * Makes this view view the C string `str` (may be `nullptr`).
58 *
59 * Intentionally not explicit.
60 */
61 CStringView& operator=(const char * const str) noexcept
62 {
63 _mStr = str;
64 return *this;
65 }
66
67 /*
68 * Viewed null-terminated C string (may be `nullptr`).
69 */
70 const char *data() const noexcept
71 {
72 return _mStr;
73 }
74
75 /*
76 * Alias of data().
77 */
78 operator const char *() const noexcept
79 {
80 return this->data();
81 }
82
83 /*
84 * Alias of data().
85 */
86 const char *operator*() const noexcept
87 {
88 return this->data();
89 }
90
91 /*
92 * Alias of data().
93 *
94 * data() must not return `nullptr`.
95 */
96 const char *begin() const noexcept
97 {
98 BT_ASSERT_DBG(_mStr);
99 return this->data();
100 }
101
102 /*
103 * Pointer to the null character of the viewed C string.
104 *
105 * data() must not return `nullptr`.
106 */
107 const char *end() const noexcept
108 {
109 BT_ASSERT_DBG(_mStr);
110 return _mStr + this->len();
111 }
112
113 /*
114 * Length of the viewed C string, excluding the null character.
115 *
116 * data() must not return `nullptr`.
117 */
118 std::size_t len() const noexcept
119 {
120 BT_ASSERT_DBG(_mStr);
121 return std::strlen(_mStr);
122 }
123
124 /*
125 * Returns an `std::string` instance containing a copy of the viewed
126 * C string.
127 *
128 * data() must not return `nullptr`.
129 */
130 std::string str() const
131 {
132 BT_ASSERT_DBG(_mStr);
133 return std::string {_mStr};
134 }
135
136 /*
137 * Alias of str().
138 */
139 operator std::string() const
140 {
141 return this->str();
142 }
143
144 /*
145 * Returns a `bt2s::string_view` instance to view the contents,
146 * excluding the null character, of the viewed C string.
147 */
148 bt2s::string_view strView() const noexcept
149 {
150 if (_mStr) {
151 return bt2s::string_view {this->begin(), this->len()};
152 } else {
153 return {};
154 }
155 }
156
157 /*
158 * Alias of strView().
159 */
160 operator bt2s::string_view() const noexcept
161 {
162 return this->strView();
163 }
164
165 /*
166 * Returns the character at index `i`.
167 *
168 * `i` must be less than what len() returns.
169 *
170 * data() must not return `nullptr`.
171 */
172 char operator[](const std::size_t i) const noexcept
173 {
174 BT_ASSERT_DBG(_mStr);
175 BT_ASSERT_DBG(i < this->len());
176 return _mStr[i];
177 }
178
179private:
180 const char *_mStr = nullptr;
181};
182
e64addc7 183static inline const char *format_as(const CStringView& str)
339e8bc4 184{
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185 return str ? *str : "(null)";
186}
339e8bc4 187
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188namespace internal {
189
190template <typename StrT>
191const char *asConstCharPtr(StrT&& val) noexcept
192{
193 return val.data();
194}
195
196inline const char *asConstCharPtr(const char * const val) noexcept
197{
198 return val;
199}
200
201template <typename StrT>
202using ComparableWithCStringView =
203 IsOneOf<typename std::decay<StrT>::type, CStringView, std::string, const char *>;
204
205} /* namespace internal */
206
207/*
208 * Returns true if `lhs` is equal to `rhs`.
209 *
210 * `LhsT` and `RhsT` may be any of:
211 *
212 * • `const char *`
213 * • `std::string`
214 * • `CStringView`
215 *
216 * Both `lhs` and `rhs` must not have an underlying `nullptr` raw data.
217 */
218template <
219 typename LhsT, typename RhsT,
220 typename = typename std::enable_if<internal::ComparableWithCStringView<LhsT>::value>::type,
221 typename = typename std::enable_if<internal::ComparableWithCStringView<RhsT>::value>::type>
222bool operator==(LhsT&& lhs, RhsT&& rhs) noexcept
223{
224 const auto rawLhs = internal::asConstCharPtr(lhs);
225 const auto rawRhs = internal::asConstCharPtr(rhs);
226
227 BT_ASSERT_DBG(rawLhs);
228 BT_ASSERT_DBG(rawRhs);
229 return std::strcmp(rawLhs, rawRhs) == 0;
230}
231
232/*
233 * Returns true if `lhs` is not equal to `rhs`.
234 *
235 * `LhsT` and `RhsT` may be any of:
236 *
237 * • `const char *`
238 * • `std::string`
239 * • `CStringView`
240 *
241 * Both `lhs` and `rhs` must not have an underlying `nullptr` raw data.
242 */
243template <typename LhsT, typename RhsT>
244bool operator!=(LhsT&& lhs, RhsT&& rhs) noexcept
245{
246 return !(std::forward<LhsT>(lhs) == std::forward<RhsT>(rhs));
247}
248
e64addc7 249} /* namespace bt2c */
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250
251#endif /* BABELTRACE_CPP_COMMON_BT2C_C_STRING_VIEW_HPP */
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