Chromium Code Reviews Chromium Code Reviews
Issue 1499293002:
Move Rvalue references to the allowed section of the C++11 styleguide. (Closed)
Base URL: https://chromium.googlesource.com/chromium/src.git@master| OLD | NEW |
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| 1 <!DOCTYPE html> | 1 <!DOCTYPE html> |
| 2 <!-- | 2 <!-- |
| 3 Copyright 2014 The Chromium Authors. All rights reserved. | 3 Copyright 2014 The Chromium Authors. All rights reserved. |
| 4 Use of this source code is governed by a BSD-style license that can be | 4 Use of this source code is governed by a BSD-style license that can be |
| 5 found in the LICENSE file. | 5 found in the LICENSE file. |
| 6 --> | 6 --> |
| 7 <html> | 7 <html> |
| 8 <head> | 8 <head> |
| 9 <meta charset="utf-8"> | 9 <meta charset="utf-8"> |
| 10 <title>C++11 use in Chromium</title> | 10 <title>C++11 use in Chromium</title> |
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| 238 <td>Range-Based For Loops</td> | 238 <td>Range-Based For Loops</td> |
| 239 <td><code>for (<i>type</i> <i>var</i> : <i>range</i>)</code></td> | 239 <td><code>for (<i>type</i> <i>var</i> : <i>range</i>)</code></td> |
| 240 <td>Facilitates a more concise syntax for iterating over the elements | 240 <td>Facilitates a more concise syntax for iterating over the elements |
| 241 of a container (or a range of iterators) in a <code>for</code> loop</td> | 241 of a container (or a range of iterators) in a <code>for</code> loop</td> |
| 242 <td><a href="http://en.cppreference.com/w/cpp/language/range-for"> | 242 <td><a href="http://en.cppreference.com/w/cpp/language/range-for"> |
| 243 Range-based for loop</a></td> | 243 Range-based for loop</a></td> |
| 244 <td>As a rule of thumb, use <code>for (const auto& ...)</code>, <code>for (auto& ...)</code>, or <code>for (<i>concrete type</i> ...)</code>. For pointers, use <code>for (auto* ...)</code> to make clear that the copy of the loop variable is intended, and only a pointer is copied. <a href="https://groups.google.com/a/ch romium.org/forum/#!topic/chromium-dev/hpzz4EqbVmc">Discussion thread</a></td> | 244 <td>As a rule of thumb, use <code>for (const auto& ...)</code>, <code>for (auto& ...)</code>, or <code>for (<i>concrete type</i> ...)</code>. For pointers, use <code>for (auto* ...)</code> to make clear that the copy of the loop variable is intended, and only a pointer is copied. <a href="https://groups.google.com/a/ch romium.org/forum/#!topic/chromium-dev/hpzz4EqbVmc">Discussion thread</a></td> |
| 245 </tr> | 245 </tr> |
| 246 | 246 |
| 247 <tr> | 247 <tr> |
| 248 <td>Rvalue References</td> | |
| 249 <td><code>T(T&& t)</code> and <code>T& operator=(T&& t)</cod e><br/> | |
| 250 <code>template <typename T>void Function(T&& t) { ... }</code></td> | |
| 251 <td>Reference that only binds to a temporary object</td> | |
| 252 <td><a href="http://en.cppreference.com/w/cpp/language/references#Rvalue_referen ces"> | |
| 253 Rvalue references</a></td> | |
| 254 <td>As per the <a href="https://google.github.io/styleguide/cppguide.html#Rvalue _references">Google style guide</a>: Only use these to define move constructors and move assignment operators, and for perfect forwarding.<br/>Most classes shou ld not be copyable, even if movable. Continue to use DISALLOW_COPY_AND_ASSIGN (o r DISALLOW_COPY_AND_ASSIGN_WITH_MOVE_FOR_BIND if needed) in most cases. <a href= "https://groups.google.com/a/chromium.org/d/topic/chromium-dev/UnRaORb4TSw">Disc ussion thread</a> and <a href="https://groups.google.com/a/chromium.org/d/topic/ cxx/Q526tkruXpM">discussion thread</a>. | |
| 255 <br/><br/> | |
| 256 MSVC 2013 has some known bugs with rvalue references: | |
| 257 <ul> | |
| 258 <li>Exported classes generate copy constructors even if they are not used, which tries to use copy constructors on members. Use DISALLOW_COPY_AND_ASSIGN on the exported class to resolve it.</li> | |
| 259 <li>The compiler chooses a T::(T&) constructor before T::(T&&). However copy con structors should be written as T::T(const T&) and these are prioritized correctl y.</li> | |
| 260 <li>The compile does not create default move constructors, either implicitly or with the =default keyword. You must provide such constructors explicitly to crea te them.</li> | |
|
Nico
2015/12/07 19:34:46
s/the compile/the compiler/
danakj
2015/12/07 19:36:07
Yaaa oops. I typod in my patchset description abou
| |
| 261 </ul> | |
| 262 </td> | |
| 263 </tr> | |
| 264 | |
| 265 <tr> | |
| 248 <td>Standard Integers</td> | 266 <td>Standard Integers</td> |
| 249 <td>Typedefs within <code><stdint.h></code> | 267 <td>Typedefs within <code><stdint.h></code> |
| 250 and <code><inttypes></code></td> | 268 and <code><inttypes></code></td> |
| 251 <td>Provides fixed-size integers independent of platforms</td> | 269 <td>Provides fixed-size integers independent of platforms</td> |
| 252 <td><a href="http://www.cplusplus.com/reference/cstdint/"> | 270 <td><a href="http://www.cplusplus.com/reference/cstdint/"> |
| 253 <stdint.h> (cstdint)</a></td> | 271 <stdint.h> (cstdint)</a></td> |
| 254 <td>Already in common use in the codebase. Approved without discussion.</td> | 272 <td>Already in common use in the codebase. Approved without discussion.</td> |
| 255 </tr> | 273 </tr> |
| 256 | 274 |
| 257 <tr> | 275 <tr> |
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| 348 <td>Wraps an iterator so that it moves objects instead of copying them.</td> | 366 <td>Wraps an iterator so that it moves objects instead of copying them.</td> |
| 349 <td><a href="http://en.cppreference.com/w/cpp/iterator/make_move_iterator">std:: make_move_iterator</a></td> | 367 <td><a href="http://en.cppreference.com/w/cpp/iterator/make_move_iterator">std:: make_move_iterator</a></td> |
| 350 <td>Useful to move objects between containers that contain move-only types like <code>scoped_ptr</code>. <a href="https://groups.google.com/a/chromium.org/forum /#!topic/cxx/lccnUljOHQU">Discussion thread</a></td> | 368 <td>Useful to move objects between containers that contain move-only types like <code>scoped_ptr</code>. <a href="https://groups.google.com/a/chromium.org/forum /#!topic/cxx/lccnUljOHQU">Discussion thread</a></td> |
| 351 </tr> | 369 </tr> |
| 352 | 370 |
| 353 <tr> | 371 <tr> |
| 354 <td>Move Semantics</td> | 372 <td>Move Semantics</td> |
| 355 <td><code>std::move()</code></td> | 373 <td><code>std::move()</code></td> |
| 356 <td>Facilitates efficient move operations</td> | 374 <td>Facilitates efficient move operations</td> |
| 357 <td><a href="http://en.cppreference.com/w/cpp/utility/move"><code>std::move</cod e> reference</a></td> | 375 <td><a href="http://en.cppreference.com/w/cpp/utility/move"><code>std::move</cod e> reference</a></td> |
| 358 <td>Note: std::move() is allowed but writing your own move constructors is still only allowed in exceptional cases for now, see 'Rvalue References (and Move Sem antics)'. <a href='https://groups.google.com/a/chromium.org/forum/#!topic/cxx/x_ dWFxJFdbM'>Discussion thread</a></td> | 376 <td><a href='https://groups.google.com/a/chromium.org/forum/#!topic/cxx/x_dWFxJF dbM'>Discussion thread</a></td> |
| 359 </tr> | 377 </tr> |
| 360 | 378 |
| 361 <tr> | 379 <tr> |
| 362 <td>Type Traits</td> | 380 <td>Type Traits</td> |
| 363 <td>Class templates within <code><type_traits></code></td> | 381 <td>Class templates within <code><type_traits></code></td> |
| 364 <td>Allows compile-time inspection of the properties of types</td> | 382 <td>Allows compile-time inspection of the properties of types</td> |
| 365 <td><a href="http://en.cppreference.com/w/cpp/header/type_traits"> | 383 <td><a href="http://en.cppreference.com/w/cpp/header/type_traits"> |
| 366 Standard library header <type_traits></a></td> | 384 Standard library header <type_traits></a></td> |
| 367 <td>Note that not all type traits are available on all platforms (eg std::underl ying_type doesn't work in libstdc++4.6). Use judiciously. <a href='https://group s.google.com/a/chromium.org/forum/#!topic/cxx/vCxo4tZNd_M'>Discussion thread</a> </td> | 385 <td>Note that not all type traits are available on all platforms (eg std::underl ying_type doesn't work in libstdc++4.6). Use judiciously. <a href='https://group s.google.com/a/chromium.org/forum/#!topic/cxx/vCxo4tZNd_M'>Discussion thread</a> </td> |
| 368 </tr> | 386 </tr> |
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| 454 <td>Raw String Literals</td> | 472 <td>Raw String Literals</td> |
| 455 <td><code>string <i>var</i>=R"(<i>raw_string</i>)";</code></td> | 473 <td><code>string <i>var</i>=R"(<i>raw_string</i>)";</code></td> |
| 456 <td>Allows a string to be encoded without any escape | 474 <td>Allows a string to be encoded without any escape |
| 457 sequences, easing parsing in regex expressions, for example</td> | 475 sequences, easing parsing in regex expressions, for example</td> |
| 458 <td><a href="http://en.cppreference.com/w/cpp/language/string_literal"> | 476 <td><a href="http://en.cppreference.com/w/cpp/language/string_literal"> |
| 459 string literal</a></td> | 477 string literal</a></td> |
| 460 <td>Causes incorrect line numbers in MSVS2013 and gcc. Reevaluate once that work s. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/ 2kWQHbbuMHI">Discussion thread</a></td> | 478 <td>Causes incorrect line numbers in MSVS2013 and gcc. Reevaluate once that work s. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/ 2kWQHbbuMHI">Discussion thread</a></td> |
| 461 </tr> | 479 </tr> |
| 462 | 480 |
| 463 <tr> | 481 <tr> |
| 464 <td>Rvalue References (and Move Semantics)</td> | |
| 465 <td><code>T(T&& t)</code> and <code>T& operator=(T&& t)</cod e></td> | |
| 466 <td>Reference that only binds to a temporary object</td> | |
| 467 <td><a href="http://en.cppreference.com/w/cpp/language/references#Rvalue_referen ces"> | |
| 468 Rvalue references</a></td> | |
| 469 <td>To be revisited in the future. Allowed in exceptional cases where approved by the OWNERS of src/styleguide/c++/. <a href="https://groups.google.com/a/chrom ium.org/d/topic/chromium-dev/UnRaORb4TSw">Discussion thread</a></td> | |
| 470 </tr> | |
| 471 | |
| 472 <tr> | |
| 473 <td>(Uniform) Initialization Syntax</td> | 482 <td>(Uniform) Initialization Syntax</td> |
| 474 <td><code><i>type</i> <i>name</i> { [<i>value</i> ..., <i>value</i>]};</code></t d> | 483 <td><code><i>type</i> <i>name</i> { [<i>value</i> ..., <i>value</i>]};</code></t d> |
| 475 <td>Allows any object of primitive, aggregate or class | 484 <td>Allows any object of primitive, aggregate or class |
| 476 type to be initialized using brace syntax</td> | 485 type to be initialized using brace syntax</td> |
| 477 <td>TODO: documentation link</td> | 486 <td>TODO: documentation link</td> |
| 478 <td>Dangerous without library support, see thread. Reevaulate once we have C++11 library support. <a href="https://groups.google.com/a/chromium.org/forum/#!topi c/chromium-dev/GF96FshwHLw">Discussion thread</a></td> | 487 <td>Dangerous without library support, see thread. Reevaulate once we have C++11 library support. <a href="https://groups.google.com/a/chromium.org/forum/#!topi c/chromium-dev/GF96FshwHLw">Discussion thread</a></td> |
| 479 </tr> | 488 </tr> |
| 480 | 489 |
| 481 <tr> | 490 <tr> |
| 482 <td>UTF-16 and UTF-32 Support (16-Bit and 32-Bit Character Types)</td> | 491 <td>UTF-16 and UTF-32 Support (16-Bit and 32-Bit Character Types)</td> |
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| 1063 C++ Style Guide</a>. However, may be useful for | 1072 C++ Style Guide</a>. However, may be useful for |
| 1064 consuming non-ASCII data.</td> | 1073 consuming non-ASCII data.</td> |
| 1065 </tr> | 1074 </tr> |
| 1066 | 1075 |
| 1067 </tbody> | 1076 </tbody> |
| 1068 </table> | 1077 </table> |
| 1069 | 1078 |
| 1070 </div> | 1079 </div> |
| 1071 </body> | 1080 </body> |
| 1072 </html> | 1081 </html> |
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