styleguide/c++/c++11.html

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  21 <h1>C++11 use in Chromium</h1>
  22
  23 <p><i>This document lives at src/styleguide/c++/c++11.html in a Chromium
  24 checkout.</i></p>
  25
  26 <p>This document summarizes the features of C++11 (both in the language itself
  27 and in enhancements to the Standard Library) and describes which features are
  28 allowed in Chromium and contains pointers to more detailed information. The
  29 Guide applies to Chromium and its subprojects. Subprojects can choose to be
  30 more restrictive if they need to compile on more toolchains than Chromium.</p>
  31
  32 <p>You can propose to make a feature available or to ban a
  33 feature by sending an email to chromium-dev. Ideally include a short blurb
  34 on what the feature is, and why you think it should or should not be allowed.
  35 Ideally, the list will arrive at some consensus and the wiki page will be
  36 updated to mention that consensus. If there's no consensus,
  37 <code>src/styleguide/C++/OWNERS</code> get to decide -- for divisive features, we expect
  38 the decision to be to not use the feature yet and possibly discuss it again a
  39 few months later, when we have more experience with the language.</p>
  40
  41 <p class="warning">Unless otherwise noted, <strong>no</strong> C++11
  42 <strong>library</strong> features are allowed.</p>
  43
  44 <h2 id="whitelist">C++11 Allowed Features</h2>
  45
  46 <p>The following features are currently allowed.</p>
  47
  48 <table id="whitelist_lang_list" class="unlined striped">
  49 <tbody>
  50
  51 <tr>
  52 <th style='width:220px;'>Feature</th>
  53 <th style='width:260px;'>Snippet</th>
  54 <th style='width:240px;'>Description</th>
  55 <th style='width:240px;'>Documentation Link</th>
  56 <th style='width:240px;'>Notes and Discussion Thread</th>
  57 </tr>
  58
  59 <tr>
  60 <td>Aliases</td>
  61 <td><code>using <i>new_alias</i> = <i>typename</i></code></td>
  62 <td>Allow parameterized typedefs</td>
  63 <td><a href="http://en.cppreference.com/w/cpp/language/type_alias">Type alias (using syntax)</a></td>
  64 <td>Use instead of typedef, unless the header needs to be compatible with C. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/8dOAMzgR4ao">Discussion thread</a></td>
  65 </tr>
  66
  67 <tr>
  68 <td>Angle Bracket Parsing in Templates</td>
  69 <td><code>&gt;&gt;</code> for <code>&gt; &gt;</code> and <br />
  70 <code>&lt;::</code> for <code>&lt; ::</code></td>
  71 <td>More intuitive parsing of template parameters</td>
  72 <td><a href="http://stackoverflow.com/questions/15785496/c-templates-angle-brackets-pitfall-what-is-the-c11-fix">
  73 C++ Templates Angle Brackets Pitfall</a></td>
  74 <td>Recommended to increase readability. Approved without discussion.</td>
  75 </tr>
  76
  77 <tr>
  78 <td>Automatic Types</td>
  79 <td><code>auto</code></td>
  80 <td>Automatic type deduction</td>
  81 <td>TODO: documentation link</td>
  82 <td>Use according to the <a
  83 href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#auto">Google
  84 Style Guide on <code>auto</code></a>. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/OQyYSfH9m2M">Discussion thread</a>. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/5-Bt3BJzAo0">Another discussion thread</a>.</td>
  85 </tr>
  86
  87 <tr>
  88 <td>Declared Type Accessor</td>
  89 <td><code>decltype(<i>expression</i>)</code></td>
  90 <td>Provides a means to determine the type of an expression at compile-time,
  91 useful most often in templates.</td>
  92 <td><a href="http://en.cppreference.com/w/cpp/language/decltype">
  93 decltype specifier</a></td>
  94 <td>Usage should be rare. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/_zoNvZd_dSo">Discussion thread</a></td>
  95 </tr>
  96
  97 <tr>
  98 <td>Default Function Creation</td>
  99 <td><code><i>Function</i>(<i>arguments</i>) = default;</code></td>
 100 <td>Instructs the compiler to generate a default version
 101 of the indicated function</td>
 102 <td><a href="http://stackoverflow.com/questions/823935/whats-the-point-in-defaulting-functions-in-c11">
 103 What's the point in defaulting functions in C++11?</a></td>
 104 <td>Doesn't work for move constructors and move assignment operators in MSVC2013.
 105 <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/qgU4mh_MpGA">Discussion thread</a></td>
 106 </tr>
 107
 108 <tr>
 109 <td>Delegated Constructors</td>
 110 <td><code>Class() : Class(0) {}</code><br />
 111 <code>Class(<i>type</i> <i>var</i>) : Class(<i>var</i>, 0)</code></td>
 112 <td>Allow overloaded constructors to use common initialization code</td>
 113 <td><a href="https://www.ibm.com/developerworks/community/blogs/5894415f-be62-4bc0-81c5-3956e82276f3/entry/introduction_to_the_c_11_feature_delegating_constructors?lang=en">
 114 Introduction to the C++11 feature: delegating constructors</a></td>
 115 <td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/0zVA8Ctx3Xo">Discussion thread</a></td>
 116 </tr>
 117
 118 <tr>
 119 <td>Enumerated Type Classes and Enum Bases</td>
 120 <td><code>enum class <i>classname</i></code><br>
 121     <code>enum class <i>classname</i> : <i>base-type</i></code><br>
 122     <code>enum <i>enumname</i> : <i>base-type</i></code></td>
 123 <td>Provide enums as full classes, with no implicit
 124 conversion to booleans or integers. Provide an explicit underlying type for
 125 enum classes and regular enums.</td>
 126 <td><a href="http://www.stroustrup.com/C++11FAQ.html#enum">enum-class</a></td>
 127 <td>Enum classes are still enums and follow enum naming rules
 128 (which means SHOUTY_CASE in the <a href="http://www.chromium.org/developers/coding-style#Naming">current style guide</a>).
 129 <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/Q5WmkAImanc">Discussion thread</a></td>
 130 </tr>
 131
 132 <tr>
 133 <td>Final Specifier</td>
 134 <td><code>final</code></td>
 135 <td> Indicates that a class or function is final and cannot be overridden</td>
 136 <td><a href="http://en.cppreference.com/w/cpp/language/final">final Language Reference</a></td>
 137 <td>Recommended for new code. Existing uses of the <code>FINAL</code> macro will be <a href="https://crbug.com/417463">replaced throughout the codebase</a>. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/VTNZzizN0zo">Discussion thread</a></td>
 138 </tr>
 139
 140 <tr>
 141 <td>Function Suppression</td>
 142 <td><code><i>Function</i>(<i>arguments</i>) = delete;</code></td>
 143 <td>Suppresses the implementation of a function, especially a
 144 synthetic function such as a copy constructor</td>
 145 <td>TODO: documentation link</td>
 146 <td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/i1o7-RNRnMs">Discussion thread</a></td>
 147 </tr>
 148
 149 <tr>
 150 <td>Lambda Expressions</td>
 151 <td><code>[<i>captures</i>](<i>params</i>) -&gt; <i>ret</i> { <i>body</i> }</code></td>
 152 <td>Anonymous functions</td>
 153 <td><a href="http://en.cppreference.com/w/cpp/language/lambda">Lambda functions</a></td>
 154 <td>Do not bind or store lambdas; use <code>base::Bind</code> and
 155 <code>base::Callback</code> instead, because they offer protection against a
 156 large class of object lifetime mistakes. Don't use default captures
 157 (<code>[=]</code>, <code>[&amp;]</code> &ndash; <a
 158   href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Lambda_expressions">Google Style Guide</a>).
 159 Lambdas are typically useful as a parameter to methods or
 160 functions that will use them immediately, such as those in
 161 <code>&lt;algorithm&gt;</code>. <a
 162   href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/D9UnnxBnciQ">Discussion
 163   thread</a></td>
 164 </tr>
 165
 166 <tr>
 167 <td>Local Types as Template Arguments</td>
 168 <td></td>
 169 <td>Allows local and unnamed types as template arguments</td>
 170 <td><a href="http://stackoverflow.com/questions/742607/using-local-classes-with-stl-algorithms">
 171 Local types, types without linkage and unnamed types as template arguments</a></td>
 172 <td>Usage should be rare. Approved without discussion.</td>
 173 </tr>
 174
 175 <tr>
 176 <td>Non-Static Class Member Initializers</td>
 177 <td>
 178 <code>
 179 class C {<br />
 180   <i>type</i> <i>var</i> = <i>value</i>;<br/>
 181   C()  // copy-initializes <i>var</i><br/>
 182 </code>
 183 <td>Allows non-static class members to be initialized at their definitions (outside constructors)</td>
 184 <td><a href="http://en.cppreference.com/w/cpp/language/data_members">
 185 Non-static data members</a></td>
 186 <td><a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Initialization">Google
 187 Style Guide</a>.
 188 <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/zqB-DySA4V0">Discussion thread</a>
 189 </td>
 190 </tr>
 191
 192 <tr>
 193 <td>Null Pointer Constant</td>
 194 <td><code>nullptr</code></td>
 195 <td>Declares a type-safe null pointer</td>
 196 <td>TODO: documentation link</td>
 197 <td>Recommended for new code.
 198 <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/4mijeJHzxLg">Discussion thread</a>.
 199 <a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#0_and_nullptr/NULL">Google Style Guide</a>.
 200 Note: <code>std::nullptr_t</code> is a library feature and not available.
 201 </td>
 202 </tr>
 203
 204 <tr>
 205 <td>Override Specifier</td>
 206 <td><code>override</code></td>
 207 <td>Indicates that a class or function overrides a base implementation</td>
 208 <td><a href="http://en.cppreference.com/w/cpp/language/override">override Language Reference</a></td>
 209 <td>Recommended for new code. Existing uses of the <code>OVERRIDE</code> macro will be <a href="https://crbug.com/417463">replaced throughout the codebase</a>. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/VTNZzizN0zo">Discussion</a></td>
 210 </tr>
 211
 212 <tr>
 213 <td>Range-Based For Loops</td>
 214 <td><code>for (<i>type</i> <i>var</i> : <i>range</i>)</code></td>
 215 <td>Facilitates a more concise syntax for iterating over the elements
 216 of a container (or a range of iterators) in a <code>for</code> loop</td>
 217 <td>TODO: documentation link</td>
 218 <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/chromium.org/forum/#!topic/chromium-dev/hpzz4EqbVmc">Discussion thread</a></td>
 219 </tr>
 220
 221 <tr>
 222 <td>Standard Integers</td>
 223 <td>Typedefs within <code>&lt;stdint.h&gt;</code>
 224 and <code>&lt;inttypes&gt;</code></td>
 225 <td>Provides fixed-size integers independent of platforms</td>
 226 <td><a href="http://www.cplusplus.com/reference/cstdint/">
 227 &lt;stdint.h&gt; (cstdint)</a></td>
 228 <td>Already in common use in the codebase. Approved without discussion.</td>
 229 </tr>
 230
 231 <tr>
 232 <td>Static Assertions</td>
 233 <td><code>static_assert(<i>bool</i>, <i>string</i>)</code></td>
 234 <td>Tests compile-time conditions</td>
 235 <td><a href="http://en.cppreference.com/w/cpp/language/static_assert">Static Assertion</a></td>
 236 <td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/POISBQEhGzU">Discussion thread</a></td>
 237 </tr>
 238
 239 <tr>
 240 <td>Variadic Macros</td>
 241 <td><code>#define <i>MACRO</i>(...) <i>Impl</i>(<i>args</i>, __VA_ARGS__)</code></td>
 242 <td>Allows macros that accept a variable number of arguments</td>
 243 <td><a href="http://stackoverflow.com/questions/4786649/are-variadic-macros-nonstandard">
 244 Are Variadic macros nonstandard?</a></td>
 245 <td>Usage should be rare. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/sRx9j3CQqyA">Discussion thread</a></td>
 246 </tr>
 247
 248 <tr>
 249 <td>Variadic Templates</td>
 250 <td><code>template &lt;<i>typename</i> ... <i>arg</i>&gt;</code></td>
 251 <td>Allows templates that accept a variable number of arguments</td>
 252 <td>TODO: documentation link</td>
 253 <td>Usage should be rare. Use instead of .pump files. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/6ItymeMXpMc">Discussion thread</a></td>
 254 </tr>
 255
 256 </tbody>
 257 </table>
 258
 259 <h2 id="blacklist">C++11 Blacklist (Disallowed and Banned Features)</h2>
 260
 261 <p>This section lists features that are not allowed to be used yet.
 262
 263 <h3 id="blacklist_banned">C++11 Banned Features</h3>
 264
 265 <p>This section lists C++11 features that are not allowed in the Chromium
 266 codebase.
 267 </p>
 268
 269 <table id="banned_list" class="unlined striped">
 270 <tbody>
 271
 272 <tr>
 273 <th style='width:240px;'>Feature or Library</th>
 274 <th style='width:240px;'>Snippet</th>
 275 <th style='width:240px;'>Description</th>
 276 <th style='width:240px;'>Documentation Link</th>
 277 <th style='width:240px;'>Notes</th>
 278 </tr>
 279
 280 <tr>
 281 <td>Constant Expressions</td>
 282 <td><code>constexpr</code></td>
 283 <td>Compile-time constant expressions</td>
 284 <td>TODO: documentation link</td>
 285 <td>Doesn't work in MSVS2013. Reevalute once it does. <a
 286 href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Use_of_constexpr">Google
 287 Style Guide on <code>constexpr</code></a></td>
 288 </tr>
 289
 290 <tr>
 291 <td>Explicit Conversion Operators</td>
 292 <td><code>explicit operator <i>type</i>() {
 293 <br />&nbsp;&nbsp;// code<br /> }</code></td>
 294 <td>Allows conversion operators that cannot be implicitly invoked</td>
 295 <td><a href="http://en.cppreference.com/w/cpp/language/explicit">
 296 explicit specifier</a></td>
 297 <td><a href="https://connect.microsoft.com/VisualStudio/feedback/details/811334/bug-in-vs-2013-support-for-explicit-conversion-operators">Doesn't work in MSVS2013</a>. Reevaluate once it does. <a href="https://groups.google.com/a/chromium.org/d/msg/chromium-dev/zGF1SrQ-1HQ/BAiC12vwPeEJ">Discussion thread</a></td>
 298 </tr>
 299
 300 <tr>
 301 <td>Function Local Variable</td>
 302 <td><code>__func__</code></td>
 303 <td>Provides a local variable of the name of the enclosing
 304 function for logging purposes</td>
 305 <td><a href="http://www.informit.com/guides/content.aspx?g=cplusplus&amp;seqNum=338">
 306 The __func__ Predeclared Identifier is Coming to C++</a></td>
 307 <td>Doesn't work in MSVS2013. Reevaluate once it does. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/ojGfcgSDzHM">Discussion thread</a></td>
 308 </tr>
 309
 310 <tr>
 311 <td>Inherited Constructors</td>
 312 <td><code>class Derived : Base {
 313 <br />&nbsp;&nbsp;using Base::Base;
 314 <br />};</code></td>
 315 <td>Allow derived classes to inherit constructors from base classes</td>
 316 <td><a href="http://en.cppreference.com/w/cpp/language/using_declaration">Using-declaration</a></td>
 317 <td>Doesn't work in MSVS2013. Reevaluate once it does. <a
 318 href="https://groups.google.com/a/chromium.org/d/msg/chromium-dev/BULzgIKZ-Ao/PLO7_GoVNvYJ">Discussion thread</a></td>
 319 </tr>
 320
 321 <tr>
 322 <td><code>long long</code> Type</td>
 323 <td><code>long long <i>var</i>= <i>value</i>;</code></td>
 324 <td>An integer of at least 64 bits</td>
 325 <td><a href="http://en.cppreference.com/w/cpp/language/types">
 326 Fundamental types</a></td>
 327 <td>Use an stdint.h type if you need a 64bit number. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/RxugZ-pIDxk">Discussion thread</a></td>
 328 </tr>
 329
 330 <tr>
 331 <td>Raw String Literals</td>
 332 <td><code>string <i>var</i>=R&quot;(<i>raw_string</i>)&quot;;</code></td>
 333 <td>Allows a string to be encoded without any escape
 334 sequences, easing parsing in regex expressions, for example</td>
 335 <td>TODO: documentation link</td>
 336 <td>Causes incorrect line numbers in MSVS2014 and gcc. Reevaluate once that works. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/2kWQHbbuMHI">Discussion thread</a></td>
 337 </tr>
 338
 339 <tr>
 340 <td>Rvalue References (and Move Semantics)</td>
 341 <td><code>T(T&amp;&amp; t)</code> and <code>T&amp; operator=(T&amp;&amp; t)</code></td>
 342 <td>Reference that only binds to a temporary object</td>
 343 <td>TODO: documentation link</td>
 344 <td>To be revisited in the future.  Allowed in exceptional cases where approved by the OWNERS of src/styleguide/c++/.</td>
 345 </tr>
 346
 347 <tr>
 348 <td>(Uniform) Initialization Syntax</td>
 349 <td><code><i>type</i> <i>name</i> { [<i>value</i> ..., <i>value</i>]};</code></td>
 350 <td>Allows any object of primitive, aggregate or class
 351 type to be initialized using brace syntax</td>
 352 <td>TODO: documentation link</td>
 353 <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/#!topic/chromium-dev/GF96FshwHLw">Discussion thread</a></td>
 354 </tr>
 355
 356 <tr>
 357 <td>UTF-16 and UTF-32 Support (16-Bit and 32-Bit Character Types)</td>
 358 <td><code>char16_t</code> and <code>char32_t</code></td>
 359 <td>Provides character types for handling 16-bit
 360 and 32-bit code units (useful for encoding
 361 UTF-16 and UTF-32 string data)</td>
 362 <td><a href="http://en.cppreference.com/w/cpp/language/types">
 363 Fundamental types</a></td>
 364 <td>Doesn't work in MSVS2013. Reevaluate once it does.  Non-UTF-8 text is
 365 banned by the
 366 <a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Non-ASCII_Characters">
 367 C++ Style Guide</a>. However, may be useful for
 368 consuming non-ASCII data. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/ME2kL7_Kvyk">Discussion thread</a></td>
 369 </tr>
 370
 371 <tr>
 372 <td>UTF-8, UTF-16, UTF-32 String Literals</td>
 373 <td><code>u8&quot;<i>string</i>&quot;, u&quot;<i>string</i>&quot;, U&quot;<i>string</i>&quot;</code></td>
 374 <td>Enforces UTF-8, UTF-16, UTF-32 encoding on all string literals</td>
 375 <td><a href="http://en.cppreference.com/w/cpp/language/string_literal">
 376 string literal</a></td>
 377 <td>Does not yet work in MSVS2013. Reevaluate once it does. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/gcoUbcjfsII">Discussion thread</a></td>
 378 </tr>
 379
 380 </tbody>
 381 </table>
 382
 383 <h3 id="blacklist_review">C++11 Features To Be Discussed</h3>
 384
 385 <p>The following C++ language features are currently disallowed.
 386 See the top of this page on how to propose moving a feature from this list
 387 into the allowed or banned sections. Note that not all of these features
 388 work in all our compilers yet.</p>
 389
 390 <table id="blacklist_review_list" class="unlined striped">
 391 <tbody>
 392
 393 <tr>
 394 <th style='width:240px;'>Feature</th>
 395 <th style='width:240px;'>Snippet</th>
 396 <th style='width:240px;'>Description</th>
 397 <th style='width:240px;'>Documentation Link</th>
 398 <th style='width:240px;'>Notes</th>
 399 </tr>
 400
 401 <tr>
 402 <td>Alignment Features</td>
 403 <td>
 404 <code>alignas</code> specifier,
 405 <code>std::alignment_of&lt;T&gt;</code>,
 406 <code>std::aligned_union&lt;Size, ...Types&gt;</code> and
 407 <code>std::max_align_t</code></td>
 408 <td>Object alignment</td>
 409 <td><a href="http://en.cppreference.com/w/cpp/types/alignment_of">std::alignment_of</a></td>
 410 <td></td>
 411 </tr>
 412
 413 <tr>
 414 <td>Attributes</td>
 415 <td><code>[[<i>attribute_name</i>]]</code></td>
 416 <td>Attaches properties to declarations that
 417 specific compiler implementations may use.</td>
 418 <td><a href="http://www.codesynthesis.com/~boris/blog/2012/04/18/cxx11-generalized-attributes/">
 419 C++11 generalized attributes</a></td>
 420 <td></td>
 421 </tr>
 422
 423 <tr>
 424 <td>Default Function Template Arguments</td>
 425 <td><code>template &lt;typename T = <i>type</i>&gt; <br />
 426 &nbsp;&nbsp;<i>type</i> <i>Function</i>(T <i>var</i>) {}</code></td>
 427 <td>Allow function templates, like classes, to have default arguments</td>
 428 <td><a href="http://stackoverflow.com/questions/2447458/default-template-arguments-for-function-templates">
 429 Default Template Arguments for Function Templates</a></td>
 430 <td></td>
 431 </tr>
 432
 433 <tr>
 434 <td>Exception Features</td>
 435 <td><code>noexcept</code>, <code>exception_ptr</code>,
 436 <code>current_exception()</code>, <code>rethrow_exception</code>,
 437 and <code>nested_exception</code></td>
 438 <td>Enhancements to exception throwing and handling</td>
 439 <td><a href="http://en.cppreference.com/w/cpp/error/exception">
 440 std::exception</a></td>
 441 <td>Exceptions are banned by the
 442 <a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Exceptions"> C++ Style Guide</a>. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/8i4tMqNpHhg">Discussion thread</a></td>
 443 </tr>
 444
 445 <tr>
 446 <td>Inline Namespaces</td>
 447 <td><code>inline</code></td>
 448 <td>Allows better versioning of namespaces</td>
 449 <td><a href="http://en.cppreference.com/w/cpp/language/namespace">Namespaces</a></td>
 450 <td>Unclear how it will work with components</td>
 451 </tr>
 452
 453 <tr>
 454 <td>Union Class Members</td>
 455 <td><code>union <i>name</i> { <i>class</i> <i>var</i>}</code></td>
 456 <td>Allows class type members</td>
 457 <td><a href="http://en.cppreference.com/w/cpp/language/union">
 458 Union declarations</a></td>
 459 <td></td>
 460 </tr>
 461
 462 <tr>
 463 <td>User-Defined Literals</td>
 464 <td><code><i>type</i> <i>var</i> = <i>literal_value</i>_<i>type</i></code></td>
 465 <td>Allows user-defined literal expressions</td>
 466 <td>TODO: documentation link</td>
 467 <td></td>
 468 </tr>
 469
 470 </tbody>
 471 </table>
 472
 473 <h3 id="blacklist_stdlib">C++11 Standard Library features</h3>
 474
 475 <details>
 476
 477 <p><summary class="note">All C++11 <strong>Standard Library features are currently
 478 banned</strong>, because they are not supported on all of our toolchains yet.
 479 In particular, chromium/android is currently using STLport, and chromium/mac is
 480 currently using libstdc++4.2, which predate C++11.
 481 </summary></p>
 482
 483 <table id="banned_stdlib" class="unlined striped">
 484
 485 <tbody>
 486 <tr>
 487 <th style='width:240px;'>Feature</th>
 488 <th style='width:240px;'>Snippet</th>
 489 <th style='width:240px;'>Description</th>
 490 <th style='width:240px;'>Documentation Link</th>
 491 <th style='width:240px;'>Style Guide Usage</th>
 492 </tr>
 493
 494 <tr>
 495 <td>Address Retrieval</td>
 496 <td><code>std::addressof()</code></td>
 497 <td>Obtains the address of an object even with overloaded <code>operator&amp;</code></td>
 498 <td><a href="http://en.cppreference.com/w/cpp/memory/addressof">std::addressof</a></td>
 499 <td>Usage should be rare as
 500 <a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Operator_Overloading">
 501 Operator Overloading</a> is rare and <code>&amps;</code>
 502 should suffice in most cases. May be preferable
 503 over <code>&amps;</code> for performing object
 504 identity checks.</td>
 505 </tr>
 506
 507 <tr>
 508 <td>Aligned Storage</td>
 509 <td><code>std::aligned_storage&lt;Size, Align&gt;::type</code></td>
 510 <td>Declare uninitialized storage having a specified alignment.</td>
 511 <td><a href="http://en.cppreference.com/w/cpp/types/aligned_storage">std::aligned_storage</a></td>
 512 <td>Note: <code>std::aligned_storage</code> is allowed, but some other C++11
 513 alignment features are still disallowed.</td>
 514 </tr>
 515
 516 <tr>
 517 <td>Allocator Traits</td>
 518 <td><code>std::allocator_traits</code></td>
 519 <td>Provides an interface for accessing custom allocators</td>
 520 <td><a href="http://en.cppreference.com/w/cpp/memory/allocator_traits">
 521 std::allocator_traits</a></td>
 522 <td>Usage should be rare.</td>
 523 </tr>
 524
 525 <tr>
 526 <td>Atomics</td>
 527 <td><code>std::atomic</code> and others in <code>&lt;atomic&gt;</code></td>
 528 <td>Fine-grained atomic types and operations</td>
 529 <td><a href="http://en.cppreference.com/w/cpp/atomic">&lt;atomic&gt;</a></td>
 530 <td></td>
 531 </tr>
 532
 533 <tr>
 534 <td>Arrays</td>
 535 <td><code>std::array</code></td>
 536 <td>A fixed-size replacement for built-in arrays, with STL support</td>
 537 <td><a href="http://en.cppreference.com/w/cpp/container/array">
 538 std::array</a></td>
 539 <td></td>
 540 </tr>
 541
 542 <tr>
 543 <td>Begin and End Non-Member Functions</td>
 544 <td><code>std::begin()</code> and <code>std::end()</code></td>
 545 <td>Allows use of free functions on any container, including
 546 built-in arrays</td>
 547 <td><a href="http://en.cppreference.com/w/cpp/iterator/begin">
 548 std::begin</a> and
 549 <a href="http://en.cppreference.com/w/cpp/iterator/end">
 550 std::end</a></td>
 551 <td>Useful for built-in arrays.</td>
 552 </tr>
 553
 554 <tr>
 555 <td>Bind Operations</td>
 556 <td><code>std::bind(<i>function</i>, <i>args</i>, ...)</code></td>
 557 <td>Declares a function object bound to certain arguments</td>
 558 <td>TODO: documentation link</td>
 559 <td></td>
 560 </tr>
 561
 562 <tr>
 563 <td>C Floating-Point Environment</td>
 564 <td><code>&lt;cfenv&gt;</code></td>
 565 <td>Provides floating point status flags and control modes for C-compatible code</td>
 566 <td><a href="http://en.cppreference.com/w/cpp/header/cfenv">Standard library header &lt;cfenv&gt;</a></td>
 567 <td>Compilers do not support use</td>
 568 </tr>
 569
 570 <tr>
 571 <td>Chrono Library</td>
 572 <td><code>&lt;chrono&gt;</code></td>
 573 <td>Provides a standard date and time library</td>
 574 <td><a href="http://en.cppreference.com/w/cpp/chrono">Date and time utilities</a></td>
 575 <td></td>
 576 </tr>
 577
 578 <tr>
 579 <td>Complex Inverse Trigonometric and Hyperbolic Functions</td>
 580 <td>Functions within <code>&lt;complex&gt;</code></td>
 581 <td>Adds inverse trigonomentric and hyperbolic non-member functions to
 582 the <code>&lt;complex&gt;</code> library.</td>
 583 <td><a href="http://en.cppreference.com/w/cpp/numeric/complex">std::complex</a></td>
 584 <td></td>
 585 </tr>
 586
 587 <tr>
 588 <td>Conditional Type Selection</td>
 589 <td><code>std::enable_if</code> and <code>std::conditional</code></td>
 590 <td>Enables compile-time conditional type selection</td>
 591 <td><a href="http://en.cppreference.com/w/cpp/types/enable_if">
 592 std::enable_if</a> and
 593 <a href="http://en.cppreference.com/w/cpp/types/conditional">
 594 conditional</a></td>
 595 <td></td>
 596 </tr>
 597
 598 <tr>
 599 <td>Constant Iterator Methods on Containers</td>
 600 <td><code>std::cbegin()</code> and <code>std::cend()</code></td>
 601 <td>Enforces iteration methods that don't change container contents</td>
 602 <td>TODO: documentation link</td>
 603 <td></td>
 604 </tr>
 605
 606 <tr>
 607 <td>Construct Elements in Containers</td>
 608 <td><code>emplace()</code>,<code>emplace_back()</code>,
 609 <code>emplace_front()</code>, <code>emplace_hint()</code></td>
 610 <td>Constructs elements directly within a container without a copy
 611 or a move</td>
 612 <td>TODO: documentation link</td>
 613 <td>Use where element construction within a container
 614 is needed.</td>
 615 </tr>
 616
 617 <tr>
 618 <td>Container Compaction Functions</td>
 619 <td><code>std::vector::shrink_to_fit()</code>,
 620 <code>std::deque::shrink_to_fit()</code>, and
 621 <code>std::string::shrink_to_fit()</code></td>
 622 <td>Requests the removal of unused space
 623 in the container</td>
 624 <td><a href="http://en.cppreference.com/w/cpp/container/vector/shrink_to_fit">
 625 std::vector::shrink_to_fit</a>,
 626 <a href="http://en.cppreference.com/w/cpp/container/deque/shrink_to_fit">
 627 std::deque::shrink_to_fit</a>, and
 628 <a href="http://en.cppreference.com/w/cpp/string/basic_string/shrink_to_fit">
 629 std::basic_string::shrink_to_fit</a></td>
 630 <td></td>
 631 </tr>
 632
 633 <tr>
 634 <td>Date/Time String Formatting Specifiers</td>
 635 <td><code>std::strftime()</code></td>
 636 <td>Converts date and time information into a
 637 formatted string using new specifiers</td>
 638 <td><a href="http://en.cppreference.com/w/cpp/chrono/c/strftime">
 639 std::strftime</a></td>
 640 <td></td>
 641 </tr>
 642
 643 <tr>
 644 <td>Function Return Type Deduction</td>
 645 <td><code>std::result_of&lt;<i>Functor(ArgTypes...)</i>&gt;</code></td>
 646 <td>Extracts the return type from the type signature of
 647 a function call invocation at compile-time.</td>
 648 <td><a href="http://en.cppreference.com/w/cpp/types/result_of">
 649 std::result_of</a></td>
 650 <td>
 651 <a href="http://stackoverflow.com/questions/15486951/why-does-stdresult-of-take-an-unrelated-function-type-as-a-type-argument">
 652 Why does std::result_of take an (unrelated) function type as a type argument?
 653 </a></td>
 654 </tr>
 655
 656 <tr>
 657 <td>Function Objects</td>
 658 <td><code>std::function</code></td>
 659 <td>Wraps a standard polymorphic function</td>
 660 <td>TODO: documentation link</td>
 661 <td></td>
 662 </tr>
 663
 664 <tr>
 665 <td>Forward Lists</td>
 666 <td><code>std::forward_list</code></td>
 667 <td>Provides an efficient singly linked list</td>
 668 <td><a href="http://en.cppreference.com/w/cpp/container/forward_list">
 669 std::forward_list</a></td>
 670 <td></td>
 671 </tr>
 672
 673 <tr>
 674 <td>Gamma Natural Log</td>
 675 <td><code>std::lgamma()</code></td>
 676 <td>Computes the natural log of the gamma of a
 677 floating point value</td>
 678 <td><a href="http://en.cppreference.com/w/cpp/numeric/math/lgamma">
 679 std::lgamma</a></td>
 680 <td></td>
 681 </tr>
 682
 683 <tr>
 684 <td>Garbage Collection Features</td>
 685 <td><code>std::{un}declare_reachable()</code> and
 686 <code>std::{un}declare_no_pointers()</code></td>
 687 <td>Enables garbage collection implementations</td>
 688 <td><a href="http://en.cppreference.com/w/cpp/memory/gc/declare_reachable">
 689 std::declare_reachable</a>
 690 and <a href="http://en.cppreference.com/w/cpp/memory/gc/declare_no_pointers">
 691 std::declare_no_pointers</a></td>
 692 <td></td>
 693 </tr>
 694
 695 <tr>
 696 <td>Heap Validation</td>
 697 <td><code>std::is_heap()</code></td>
 698 <td>Checks whether an iterator range is in fact a heap</td>
 699 <td>TODO: documentation link</td>
 700 <td></td>
 701 </tr>
 702
 703 <tr>
 704 <td>Is Nan</td>
 705 <td><code>std::isnan()</code></td>
 706 <td>Determines if a floating point value is not-a-number</td>
 707 <td><a href="http://en.cppreference.com/w/cpp/numeric/math/isnan">std::isnan</a></td>
 708 <td></td>
 709 </tr>
 710
 711 <tr>
 712 <td>Iterator Operators</td>
 713 <td><code>std::next()</code> and <code>std::prev()</code></td>
 714 <td>Copies an iterator and increments or decrements the copy by
 715 some value</td>
 716 <td><a href="http://en.cppreference.com/w/cpp/iterator/next">std::next</a>
 717 and <a href="http://en.cppreference.com/w/cpp/iterator/prev">std::prev</a>
 718 </td>
 719 <td></td>
 720 </tr>
 721
 722 <tr>
 723 <td>Initializer Lists</td>
 724 <td><code>std::initializer_list&lt;T&gt;</code></td>
 725 <td>Allows containers to be initialized with aggregate elements</td>
 726 <td>TODO: documentation link</td>
 727 <td></td>
 728 </tr>
 729
 730 <tr>
 731 <td>Move Semantics</td>
 732 <td><code>std::move()</code></td>
 733 <td>Facilitates efficient move operations</td>
 734 <td><a href="http://en.cppreference.com/w/cpp/utility/move">
 735 <code>std::move</code> reference</a></td>
 736 <td></td>
 737 </tr>
 738
 739 <tr>
 740 <td>Pointer Traits Class Template</td>
 741 <td><code>std::pointer_traits</code></td>
 742 <td>Provides a standard way to access properties
 743 of pointers and pointer-like types</td>
 744 <td><a href="http://en.cppreference.com/w/cpp/memory/pointer_traits">
 745 std::pointer_traits</a></td>
 746 <td>Useful for determining the element type
 747 pointed at by a (possibly smart) pointer.</td>
 748 </tr>
 749
 750 <tr>
 751 <td>Random Number Generators</td>
 752 <td>Functions within <code>&lt;random&gt;</code></td>
 753 <td>Random number generation algorithms and utilities</td>
 754 <td><a href="http://en.cppreference.com/w/cpp/numeric/random">
 755 Pseudo-random number generation</a></td>
 756 <td></td>
 757 </tr>
 758
 759 <tr>
 760 <td>Ratio Template Class</td>
 761 <td><code>std::ratio&lt;<i>numerator</i>, <i>denominator</i>&gt;</code></td>
 762 <td>Provides compile-time rational numbers</td>
 763 <td>TODO: documentation link</td>
 764 <td></td>
 765 </tr>
 766
 767 <tr>
 768 <td>Reference Wrapper Classes</td>
 769 <td><code>std::reference_wrapper</code> and
 770 <code>std::ref()</code>, <code>std::cref()</code></td>
 771 <td>Allows you to wrap a reference within a standard
 772 object (and use those within containers)</td>
 773 <td><a href="http://www.informit.com/guides/content.aspx?g=cplusplus&amp;seqNum=217">
 774 Reference Wrappers</a></td>
 775 <td></td>
 776 </tr>
 777
 778 <tr>
 779 <td>Regex Library</td>
 780 <td><code>&lt;regex&gt;</code></td>
 781 <td>Provides a standard regular expressions library</td>
 782 <td><a href="http://en.cppreference.com/w/cpp/regex">Regular expressions library</a></td>
 783 <td></td>
 784 </tr>
 785
 786 <tr>
 787 <td>Shared Pointers</td>
 788 <td><code>std::shared_ptr</code></td>
 789 <td>Allows shared ownership of a pointer through reference counts</td>
 790 <td><a href="http://en.cppreference.com/w/cpp/memory/shared_ptr">std::shared_ptr</a></td>
 791 <td><a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Ownership_and_Smart_Pointers">
 792 Ownership and Smart Pointers</a></td>
 793 </tr>
 794
 795 <tr>
 796 <td>Soft Program Exits</td>
 797 <td><code>std::at_quick_exit()</code>
 798 and <code>std::quick_exit()</code></td>
 799 <td>Allows registration of functions to be called upon exit,
 800 allowing cleaner program exit than <code>abort()</code> or
 801 <code>exit</code></td>
 802 <td><a href="http://en.cppreference.com/w/cpp/utility/program/quick_exit">
 803 std:quick_exit</a></td>
 804 <td></td>
 805 </tr>
 806
 807 <tr>
 808 <td>String Direct Reference Functions</td>
 809 <td><code>std::string::front()</code> and <code>std::string::back()</code></td>
 810 <td>Returns a reference to the front or back of a string</td>
 811 <td><a href="http://en.cppreference.com/w/cpp/string/basic_string/front">
 812 std::basic_string::front</a> and
 813 <a href="http://en.cppreference.com/w/cpp/string/basic_string/back">
 814 std::basic_string::back</a></td>
 815 <td></td>
 816 </tr>
 817
 818 <tr>
 819 <td>String to Number Functions</td>
 820 <td><code>std::stoi()</code>, <code>std::stol()</code>,
 821 <code>std::stoul()</code>, <code>std::stoll</code>, <code>std::stoull()</code>,
 822 <code>std::stof()</code>, <code>std::stod()</code>, <code>std::stold()</code>,
 823 and <code>std::to_string()</code></td>
 824 <td>Converts strings to numbers</td>
 825 <td><a href="http://en.cppreference.com/w/cpp/string/basic_string/stol">
 826 std::stoi, std::stol, std::stoll</a>,
 827 <a href="http://en.cppreference.com/w/cpp/string/basic_string/stoul">
 828 std::stoul, std::stoull</a>, and
 829 <a href="http://en.cppreference.com/w/cpp/string/basic_string/stof">
 830 std::stof, std::stod, std::stold</a> </td>
 831 <td></td>
 832 </tr>
 833
 834 <tr>
 835 <td>STL Algorithms</td>
 836 <td>Functions within <code>&lt;algorithm&gt;</code>.</td>
 837 <td>Enhancements to the set of STL algorithms</td>
 838 <td>See the <a href="http://en.cppreference.com/w/cpp/algorithm">
 839 Algorithms library</a> for a complete list.</td>
 840 <td></td>
 841 </tr>
 842
 843 <tr>
 844 <td>System Errors</td>
 845 <td><code>&lt;system_error&gt;</code></td>
 846 <td>Provides a standard system error library</td>
 847 <td><a href="http://en.cppreference.com/w/cpp/error/system_error">std::system_error</a></td>
 848 <td></td>
 849 </tr>
 850
 851 <tr>
 852 <td>Trailing Return Types</td>
 853 <td><code>auto <i>function declaration</i> -> <i>return_type</i></code></td>
 854 <td>Allows trailing function return value syntax</td>
 855 <td><a href="http://en.cppreference.com/w/cpp/language/function">
 856 Declaring functions</a></td>
 857 <td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/OQyYSfH9m2M">Discussion thread</a></td>
 858 </tr>
 859
 860 <tr>
 861 <td>Thread Library</td>
 862 <td><code>&lt;thread&gt; support, including &lt;future&gt;,
 863 &lt;mutex&gt;, &lt;condition_variable&gt;</code></td>
 864 <td>Provides a standard mulitthreading library using <code>std::thread</code> and associates</td>
 865 <td><a href="http://en.cppreference.com/w/cpp/thread">Thread support library</a></td>
 866 <td></td>
 867 </tr>
 868
 869 <tr>
 870 <td>Tuples</td>
 871 <td><code>std::tuple</code></td>
 872 <td>A fixed-size ordered collection of values of mixed types</td>
 873 <td>TODO: documentation link</td>
 874 <td></td>
 875 </tr>
 876
 877 <tr>
 878 <td>Type-Generic Math Functions</td>
 879 <td>Functions within <code>&lt;ctgmath&gt;</code></td>
 880 <td>Provides a means to call real or complex functions
 881 based on the type of arguments</td>
 882 <td><a href="http://en.cppreference.com/w/cpp/header/ctgmath">
 883 Standard library header &lt;ctgmath&gt;</a></td>
 884 <td></td>
 885 </tr>
 886
 887 <tr>
 888 <td>Type Info Enhancements</td>
 889 <td><code>std::type_index</code> and <code>std::type_info::hash_code()</code></td>
 890 <td>Allows type information (most often within containers)
 891 that can be copied, assigned, or hashed</td>
 892 <td><a href="http://en.cppreference.com/w/cpp/types/type_index">
 893 std::type_index</a> and
 894 <a href="http://en.cppreference.com/w/cpp/types/type_info/hash_code">
 895 std::type_info::hash_code</a></td>
 896 <td><code>std::type_index</code> is a thin wrapper for
 897 <code>std::type_info</code>, allowing you to use it directly
 898 within both associative and unordered containers</td>
 899 </tr>
 900
 901 <tr>
 902 <td>Type Traits</td>
 903 <td>Class templates within <code>&lt;type_traits&gt;</code></td>
 904 <td>Allows compile-time inspection of the properties of types</td>
 905 <td><a href="http://en.cppreference.com/w/cpp/header/type_traits">
 906 Standard library header &lt;type_traits&gt;</a></td>
 907 <td></td>
 908 </tr>
 909
 910 <tr>
 911 <td>Unique Pointers</td>
 912 <td><code>std::unique_ptr&lt;<i>type</i>&gt;</code></td>
 913 <td>Defines a pointer with clear and unambiguous ownership</td>
 914 <td>TODO: documentation link</td>
 915 <td><a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Ownership_and_Smart_Pointers">
 916 Ownership and Smart Pointers</a></td>
 917 </tr>
 918
 919 <tr>
 920 <td>Unordered Associative Containers</td>
 921 <td><code>std::unordered_set</code>, <code>std::unordered_map</code>,
 922 <code>std::unordered_multiset</code>, and <code>std::unordered_multimap</code></td>
 923 <td>Allows efficient containers of key/value pairs</td>
 924 <td><a href="http://en.cppreference.com/w/cpp/container/unordered_map">std::unordered_map</a>
 925 and <a href="http://en.cppreference.com/w/cpp/container/unordered_set">std::unordered_set</a>
 926 </td>
 927 <td></td>
 928 </tr>
 929
 930 <tr>
 931 <td>Variadic Copy Macro</td>
 932 <td><code>va_copy(va_list <i>dest</i>, va_list <i>src</i>)</code></td>
 933 <td>Makes a copy of the variadic function arguments</td>
 934 <td></td>
 935 <td></td>
 936 </tr>
 937
 938 <tr>
 939 <td>Weak Pointers</td>
 940 <td><code>std::weak_ptr</code></td>
 941 <td>Allows a weak reference to a <code>std::shared_ptr</code></td>
 942 <td><a href="http://en.cppreference.com/w/cpp/memory/weak_ptr">
 943 std::weak_ptr</a></td>
 944 <td><a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Ownership_and_Smart_Pointers">
 945 Ownership and Smart Pointers</a></td>
 946 </tr>
 947
 948 <tr>
 949 <td>Wide String Support</td>
 950 <td><code>std::wstring_convert</code>,
 951 <code>std::wbuffer_convert</code>.
 952 <code>std::codecvt_utf8</code>, <code>std::codecvt_utf16</code>,
 953 and <code>std::codecvt_utf8_utf16</code></td>
 954 <td>Converts between string encodings</td>
 955 <td><a href="http://en.cppreference.com/w/cpp/locale/wstring_convert">
 956 std::wstring_convert</a>,
 957 <a href="http://en.cppreference.com/w/cpp/locale/wbuffer_convert">
 958 std::wbuffer_convert</a>,
 959 <a href="http://en.cppreference.com/w/cpp/locale/codecvt_utf8">
 960 std::codecvt_utf8</a>,
 961 <a href="http://en.cppreference.com/w/cpp/locale/codecvt_utf16">
 962 std::codecvt_utf16</a>, and
 963 <a href="http://en.cppreference.com/w/cpp/locale/codecvt_utf8_utf16">
 964 std::codecvt_utf8_utf16</a>
 965 </td>
 966 <td>Non-UTF-8 text is banned by the
 967 <a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Non-ASCII_Characters">
 968 C++ Style Guide</a>. However, may be useful for
 969 consuming non-ASCII data.</td>
 970 </tr>
 971
 972 </tbody>
 973 </table>
 974
 975 </details>
 976
 977 </div>
 978 </body>
 979 </html>