| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | #include "Verbose.hpp" | ||
| 2 | #include "compat/ranges23.hpp" | ||
| 3 | #include <gtest/gtest.h> | ||
| 4 | #include <tuple> | ||
| 5 | |||
| 6 | class Zip : public testing::Test { | ||
| 7 | public: | ||
| 8 | // NOLINTBEGIN(*-avoid-magic-numbers) | ||
| 9 | |||
| 10 | 6 | void SetUp() override { | |
| 11 | 6 | left = {1, 2, 3, 4, 5}; | |
| 12 | 6 | right = {1.1, 2.2, 3.3, 4.4, 5.5}; | |
| 13 | |||
| 14 | // Carefully avoid copies and moves. | ||
| 15 | 6 | center.reserve(5); | |
| 16 |
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36 | for (const auto& name : {"one", "two", "three", "four", "five"}) { |
| 17 |
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30 | center.emplace_back(name); |
| 18 | } | ||
| 19 | 6 | } | |
| 20 | |||
| 21 | // NOLINTEND(*-avoid-magic-numbers) | ||
| 22 | |||
| 23 | template <typename T> | ||
| 24 | 16 | void print(const std::string& label, const T& range) { | |
| 25 | 16 | std::cout << label; | |
| 26 |
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156 | for (const auto& element : range) { std::cout << element << " "; } |
| 27 | 16 | std::cout << std::endl; | |
| 28 | 16 | } | |
| 29 | |||
| 30 | std::vector<int> left; | ||
| 31 | std::vector<Verbose<>> center; | ||
| 32 | std::vector<double> right; | ||
| 33 | }; | ||
| 34 | |||
| 35 | 8 | TEST_F(Zip, print) { | |
| 36 |
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6 | print("left: ", left); |
| 37 |
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6 | print("center: ", center); |
| 38 |
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6 | print("right: ", right); |
| 39 |
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8 | print("zip(left,center,right): ", |
| 40 |
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4 | std::ranges::views::zip(left, center, right)); |
| 41 | 2 | } | |
| 42 | |||
| 43 | #if __cplusplus >= 201703L // since C++17 | ||
| 44 | |||
| 45 | 8 | TEST_F(Zip, for_mutable) { | |
| 46 |
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6 | print("before: ", std::ranges::views::zip(left, center, right)); |
| 47 | |||
| 48 | // When iterating over a single sequence, convention dictates that we use | ||
| 49 | // a non-const lvalue reference. The presence of the reference makes it | ||
| 50 | // clear that no copy is being made. The absence of the const keyword makes | ||
| 51 | // it clear that the elements can be modified. | ||
| 52 |
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12 | for (auto& a : center) { a.name().append("?"); } |
| 53 | |||
| 54 | // Because each element of a zipped sequence is a temporary tuple, | ||
| 55 | // we cannot use a non-const lvalue reference in the for loop, but we can | ||
| 56 | // safely make a copy. Because the tuple contains references, we are not | ||
| 57 | // making copies of the underlying sequence elements themselves. However, | ||
| 58 | // the absence of a reference may be confusing. It looks like we are making | ||
| 59 | // copies and that any modifications affect only the copies, which would | ||
| 60 | // probably be a bug. | ||
| 61 |
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12 | for (auto [a, b, c] : std::ranges::views::zip(left, center, right)) { |
| 62 | // Verify previous modifications. | ||
| 63 |
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10 | EXPECT_EQ('?', b.name().back()); |
| 64 | // Make additional modifications. | ||
| 65 | 10 | c -= a++; | |
| 66 |
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10 | b.name().append("!"); |
| 67 | 2 | } | |
| 68 | |||
| 69 | // We could use a const lvalue reference, but the presence of the const | ||
| 70 | // keyword may be confusing. It looks like we should not be able to modify | ||
| 71 | // the sequence elements. | ||
| 72 |
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14 | for (const auto& [a, b, c] : std::ranges::views::zip(left, center, right)) { |
| 73 | // Verify previous modifications. | ||
| 74 |
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10 | EXPECT_FLOAT_EQ(0.1 * (a - 1), c); |
| 75 |
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10 | EXPECT_EQ('!', b.name().back()); |
| 76 | // Make additional modifications. | ||
| 77 | 10 | c = 1.1 * a++; // NOLINT(*-avoid-magic-numbers) | |
| 78 | 10 | b.name().pop_back(); | |
| 79 | 2 | } | |
| 80 | |||
| 81 | // The least confusing solution uses a universal reference. | ||
| 82 | // The presence of the reference makes it clear that no copy is being made. | ||
| 83 | // The absence of the const keyword makes it clear that the elements can be | ||
| 84 | // modified. | ||
| 85 |
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14 | for (auto&& [a, b, c] : std::ranges::views::zip(left, center, right)) { |
| 86 | // Verify previous modifications. | ||
| 87 |
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10 | EXPECT_FLOAT_EQ(1.1 * (a - 1), c); |
| 88 |
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10 | EXPECT_EQ('?', b.name().back()); |
| 89 | // Make additional modifications. | ||
| 90 | 10 | a -= 2; | |
| 91 | 10 | c -= 1.1; // NOLINT(*-avoid-magic-numbers) | |
| 92 | 10 | b.name().pop_back(); | |
| 93 | 2 | } | |
| 94 | |||
| 95 | // Nothing stops us from using a universal reference when iterating over a | ||
| 96 | // single sequence, though it may look unconventional. | ||
| 97 |
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12 | for (auto&& a : center) { |
| 98 |
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10 | a.name().append("*"); |
| 99 | 10 | a.name().pop_back(); | |
| 100 | 2 | } | |
| 101 | |||
| 102 |
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6 | print("after: ", std::ranges::views::zip(left, center, right)); |
| 103 | 2 | } | |
| 104 | |||
| 105 | #endif // C++17 | ||
| 106 | |||
| 107 | 8 | TEST_F(Zip, for_mutable_tuple) { | |
| 108 |
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6 | print("before: ", std::ranges::views::zip(left, center, right)); |
| 109 | |||
| 110 | // We can use a tuple instead of structured binding. We cannot use a | ||
| 111 | // non-const lvalue reference, so we use a universal reference to | ||
| 112 | // minimize confusion. (See discussion above.) | ||
| 113 |
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14 | for (auto&& tuple : std::ranges::views::zip(left, center, right)) { |
| 114 |
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10 | auto& a = std::get<0>(tuple); |
| 115 |
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10 | auto& b = std::get<1>(tuple); |
| 116 |
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10 | auto& c = std::get<2>(tuple); |
| 117 | 10 | c -= a++; | |
| 118 |
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10 | b.name().append("!"); |
| 119 | 2 | } | |
| 120 |
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14 | for (auto&& tuple : std::ranges::views::zip(left, center, right)) { |
| 121 |
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10 | auto& a = std::get<0>(tuple); |
| 122 |
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10 | auto& b = std::get<1>(tuple); |
| 123 |
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10 | auto& c = std::get<2>(tuple); |
| 124 | // Verify previous modifications. | ||
| 125 |
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10 | EXPECT_FLOAT_EQ(0.1 * (a - 1), c); |
| 126 |
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10 | EXPECT_EQ('!', b.name().back()); |
| 127 | // Put things back the way we found them. | ||
| 128 | 10 | c += --a; | |
| 129 | 10 | b.name().pop_back(); | |
| 130 | 2 | } | |
| 131 | |||
| 132 |
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6 | print("after: ", std::ranges::views::zip(left, center, right)); |
| 133 | 2 | } | |
| 134 | |||
| 135 | 8 | TEST_F(Zip, for_const) { | |
| 136 | // When iterating over a single sequence, convention dictates that we use | ||
| 137 | // a const lvalue reference when we do not intend to modify the elements. | ||
| 138 | // The presence of the reference makes it clear that no copy is being made. | ||
| 139 | // The presence of the const keyword makes it clear that the elements cannot | ||
| 140 | // be modified. | ||
| 141 |
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12 | for (const auto& a : center) { |
| 142 | // a.name().append("!"); // compile time error | ||
| 143 |
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10 | EXPECT_NE('!', a.name().back()); |
| 144 | 2 | } | |
| 145 | |||
| 146 | // When the sequence itself is const, the const keyword becomes optional, | ||
| 147 | // but we can use it anyway to make our intentions clear. This also guards | ||
| 148 | // against future changes in the declaration of the sequence. | ||
| 149 | 2 | const auto& ccenter = center; | |
| 150 |
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12 | for (const auto& a : ccenter) { |
| 151 | // a.name().append("!"); // compile time error | ||
| 152 |
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10 | EXPECT_NE('!', a.name().back()); |
| 153 | 2 | } | |
| 154 | |||
| 155 | #if __cplusplus >= 201703L // since C++17 | ||
| 156 | |||
| 157 | // To make our intentions more obvious, we can explicitly make the sequence const. | ||
| 158 |
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12 | for (const auto& a : std::as_const(center)) { |
| 159 | // a.name().append("!"); // compile time error | ||
| 160 |
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10 | EXPECT_NE('!', a.name().back()); |
| 161 | 2 | } | |
| 162 | |||
| 163 | // Unfortunately using a const lvalue reference does not have the intended | ||
| 164 | // effect when iterating over a zipped sequence. This is because each tuple | ||
| 165 | // in the zipped sequence contains non-const references. | ||
| 166 | // The tuple may be const, but the elements can still be modified! | ||
| 167 |
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22 | for (const auto& [a, b, c] : std::ranges::views::zip(left, center, right)) { |
| 168 | 10 | c -= a++; // surprise! | |
| 169 |
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10 | b.name().append("!"); // surprise! |
| 170 | 2 | } | |
| 171 | |||
| 172 | // Instead, we must ensure that the underlying sequences being zipped are | ||
| 173 | // const. The const keyword becomes optional, but we can use it anyway | ||
| 174 | // to make our intentions clear. | ||
| 175 | 2 | const auto& cleft = left; | |
| 176 | 2 | const auto& cright = right; | |
| 177 |
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24 | for (const auto& [a, b, c] : std::ranges::views::zip(cleft, ccenter, cright)) { |
| 178 |
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10 | EXPECT_EQ('!', b.name().back()); |
| 179 | // c -= a++; // compile time error | ||
| 180 | // b.name().append("!"); // compile time error | ||
| 181 | 2 | } | |
| 182 | |||
| 183 | // To make our intentions more obvious, and to guard against future changes | ||
| 184 | // in the declarations of the sequences, we can explicitly make each | ||
| 185 | // sequence const before combining them. | ||
| 186 |
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32 | for (const auto& [a, b, c] : std::ranges::views::zip( |
| 187 |
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56 | std::as_const(left), std::as_const(center), std::as_const(right))) { |
| 188 |
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10 | EXPECT_EQ('!', b.name().back()); |
| 189 | // c -= a++; // compile time error | ||
| 190 | // b.name().append("!"); // compile time error | ||
| 191 | 2 | } | |
| 192 | |||
| 193 | #endif // C++17 | ||
| 194 | |||
| 195 | #if __cplusplus >= 202302L // since C++23 | ||
| 196 | |||
| 197 | // To make our intentions more obvious, and to guard against future changes | ||
| 198 | // in the declarations of the sequences, we can explicitly make each | ||
| 199 | // sequence const before combining them. | ||
| 200 | for (const auto& [a, b, c] : | ||
| 201 | std::ranges::views::zip(left, center, right) | std::views::as_const) { | ||
| 202 | EXPECT_EQ('!', b.name().back()); | ||
| 203 | // c -= a++; // compile time error | ||
| 204 | // b.name().append("!"); // compile time error | ||
| 205 | } | ||
| 206 | |||
| 207 | #endif // C++23 | ||
| 208 | 2 | } | |
| 209 | |||
| 210 | 8 | TEST_F(Zip, for_const_tuple) { | |
| 211 | // We can use a tuple instead of structured binding. The const keyword is | ||
| 212 | // optional as it has no effect. This is because each tuple in the zipped | ||
| 213 | // sequence contains non-const references. The tuple may be const, but the | ||
| 214 | // elements could still be modified! Using const lvalue references as we | ||
| 215 | // unpack the tuple makes it clear that the elements cannot be modified. | ||
| 216 |
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24 | for (const auto& tuple : std::ranges::views::zip(left, center, right)) { |
| 217 |
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10 | const auto& a = std::get<0>(tuple); |
| 218 |
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10 | const auto& b = std::get<1>(tuple); |
| 219 |
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10 | const auto& c = std::get<2>(tuple); |
| 220 |
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10 | EXPECT_FLOAT_EQ(1.1 * a, c); |
| 221 |
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10 | EXPECT_NE('!', b.name().back()); |
| 222 | // b.name().append("!"); // compile time error | ||
| 223 | 2 | } | |
| 224 | 2 | } | |
| 225 | |||
| 226 | 8 | TEST_F(Zip, for_copy) { | |
| 227 | // When iterating over a single sequence, convention dictates that we | ||
| 228 | // avoid using a reference when we intend to make copies of the elements. | ||
| 229 | // The absence of a reference indicates that a copy is being made. | ||
| 230 | // The absence of the const keyword indicates that the copies can be modified. | ||
| 231 |
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12 | for (auto a : center) { |
| 232 |
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10 | a.name().append("!"); |
| 233 |
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10 | EXPECT_EQ('!', a.name().back()); // Verify that copy is modified. |
| 234 | 12 | } | |
| 235 |
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12 | for (const auto& a : center) { |
| 236 |
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10 | EXPECT_NE('!', a.name().back()); // Verify that original is not modified. |
| 237 | 2 | } | |
| 238 | |||
| 239 | #if __cplusplus >= 201703L // since C++17 | ||
| 240 | |||
| 241 | // Unfortunately using the same convention with a zipped sequence does not | ||
| 242 | // have the intended effect. This is because each tuple in the zipped | ||
| 243 | // sequence contains non-const references. The tuple may have been copied, | ||
| 244 | // but the original elements can still be modified! | ||
| 245 |
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24 | for (auto [a, b, c] : std::ranges::views::zip(left, center, right)) { |
| 246 | 10 | c -= a++; // surprise! | |
| 247 |
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10 | b.name().append("!"); // surprise! |
| 248 | // Put things back the way we found them. | ||
| 249 | 10 | c += --a; | |
| 250 | 10 | b.name().pop_back(); | |
| 251 | 2 | } | |
| 252 | |||
| 253 | #endif // C++17 | ||
| 254 | |||
| 255 | // The least confusing solution is to make copies as we unpack a tuple. | ||
| 256 |
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24 | for (auto tuple : std::ranges::views::zip(left, center, right)) { |
| 257 |
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10 | auto a = std::get<0>(tuple); |
| 258 |
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10 | auto b = std::get<1>(tuple); |
| 259 |
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10 | auto c = std::get<2>(tuple); |
| 260 |
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10 | EXPECT_FALSE(std::is_reference<decltype(a)>::value); |
| 261 |
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10 | EXPECT_FALSE(std::is_reference<decltype(b)>::value); |
| 262 |
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10 | EXPECT_FALSE(std::is_reference<decltype(c)>::value); |
| 263 | // Modify the copies. | ||
| 264 | 10 | c -= a++; | |
| 265 |
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10 | b.name().append("!"); |
| 266 | 12 | } | |
| 267 |
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24 | for (const auto& tuple : std::ranges::views::zip(left, center, right)) { |
| 268 |
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10 | const auto& a = std::get<0>(tuple); |
| 269 |
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10 | const auto& b = std::get<1>(tuple); |
| 270 |
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10 | const auto& c = std::get<2>(tuple); |
| 271 | // Verify that original values were not modified. | ||
| 272 |
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10 | EXPECT_FLOAT_EQ(1.1 * a, c); |
| 273 |
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10 | EXPECT_NE('!', b.name().back()); |
| 274 | 2 | } | |
| 275 | 2 | } | |
| 276 |