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><a href="http://en.cppreference.com/w/cpp/language/auto">
  82 auto specifier</a></td>
  83 <td>Use according to the <a
  84 href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#auto">Google
  85 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>
  86 </tr>
  87
  88 <tr>
  89 <td>Declared Type Accessor</td>
  90 <td><code>decltype(<i>expression</i>)</code></td>
  91 <td>Provides a means to determine the type of an expression at compile-time,
  92 useful most often in templates.</td>
  93 <td><a href="http://en.cppreference.com/w/cpp/language/decltype">
  94 decltype specifier</a></td>
  95 <td>Usage should be rare. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/_zoNvZd_dSo">Discussion thread</a></td>
  96 </tr>
  97
  98 <tr>
  99 <td>Default Function Creation</td>
 100 <td><code><i>Function</i>(<i>arguments</i>) = default;</code></td>
 101 <td>Instructs the compiler to generate a default version
 102 of the indicated function</td>
 103 <td><a href="http://stackoverflow.com/questions/823935/whats-the-point-in-defaulting-functions-in-c11">
 104 What's the point in defaulting functions in C++11?</a></td>
 105 <td>Doesn't work for move constructors and move assignment operators in MSVC2013.
 106 <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/qgU4mh_MpGA">Discussion thread</a></td>
 107 </tr>
 108
 109 <tr>
 110 <td>Delegated Constructors</td>
 111 <td><code>Class() : Class(0) {}</code><br />
 112 <code>Class(<i>type</i> <i>var</i>) : Class(<i>var</i>, 0)</code></td>
 113 <td>Allow overloaded constructors to use common initialization code</td>
 114 <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">
 115 Introduction to the C++11 feature: delegating constructors</a></td>
 116 <td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/0zVA8Ctx3Xo">Discussion thread</a></td>
 117 </tr>
 118
 119 <tr>
 120 <td>Enumerated Type Classes and Enum Bases</td>
 121 <td><code>enum class <i>classname</i></code><br>
 122     <code>enum class <i>classname</i> : <i>base-type</i></code><br>
 123     <code>enum <i>enumname</i> : <i>base-type</i></code></td>
 124 <td>Provide enums as full classes, with no implicit
 125 conversion to booleans or integers. Provide an explicit underlying type for
 126 enum classes and regular enums.</td>
 127 <td><a href="http://www.stroustrup.com/C++11FAQ.html#enum">enum-class</a></td>
 128 <td>Enum classes are still enums and follow enum naming rules
 129 (which means SHOUTY_CASE in the <a href="http://www.chromium.org/developers/coding-style#Naming">current style guide</a>).
 130 <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/Q5WmkAImanc">Discussion thread</a></td>
 131 </tr>
 132
 133 <tr>
 134 <td>Final Specifier</td>
 135 <td><code>final</code></td>
 136 <td> Indicates that a class or function is final and cannot be overridden</td>
 137 <td><a href="http://en.cppreference.com/w/cpp/language/final">final Language Reference</a></td>
 138 <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>
 139 </tr>
 140
 141 <tr>
 142 <td>Function Suppression</td>
 143 <td><code><i>Function</i>(<i>arguments</i>) = delete;</code></td>
 144 <td>Suppresses the implementation of a function, especially a
 145 synthetic function such as a copy constructor</td>
 146 <td>TODO: documentation link</td>
 147 <td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/i1o7-RNRnMs">Discussion thread</a></td>
 148 </tr>
 149
 150 <tr>
 151 <td>Lambda Expressions</td>
 152 <td><code>[<i>captures</i>](<i>params</i>) -&gt; <i>ret</i> { <i>body</i> }</code></td>
 153 <td>Anonymous functions</td>
 154 <td><a href="http://en.cppreference.com/w/cpp/language/lambda">Lambda functions</a></td>
 155 <td>Do not bind or store lambdas; use <code>base::Bind</code> and
 156 <code>base::Callback</code> instead, because they offer protection against a
 157 large class of object lifetime mistakes. Don't use default captures
 158 (<code>[=]</code>, <code>[&amp;]</code> &ndash; <a
 159   href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Lambda_expressions">Google Style Guide</a>).
 160 Lambdas are typically useful as a parameter to methods or
 161 functions that will use them immediately, such as those in
 162 <code>&lt;algorithm&gt;</code>. <a
 163   href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/D9UnnxBnciQ">Discussion
 164   thread</a></td>
 165 </tr>
 166
 167 <tr>
 168 <td>Local Types as Template Arguments</td>
 169 <td></td>
 170 <td>Allows local and unnamed types as template arguments</td>
 171 <td><a href="http://stackoverflow.com/questions/742607/using-local-classes-with-stl-algorithms">
 172 Local types, types without linkage and unnamed types as template arguments</a></td>
 173 <td>Usage should be rare. Approved without discussion.</td>
 174 </tr>
 175
 176 <tr>
 177 <td>Non-Static Class Member Initializers</td>
 178 <td>
 179 <code>
 180 class C {<br />
 181   <i>type</i> <i>var</i> = <i>value</i>;<br/>
 182   C()  // copy-initializes <i>var</i><br/>
 183 </code>
 184 <td>Allows non-static class members to be initialized at their definitions (outside constructors)</td>
 185 <td><a href="http://en.cppreference.com/w/cpp/language/data_members">
 186 Non-static data members</a></td>
 187 <td><a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Initialization">Google
 188 Style Guide</a>.
 189 <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/zqB-DySA4V0">Discussion thread</a>
 190 </td>
 191 </tr>
 192
 193 <tr>
 194 <td>Null Pointer Constant</td>
 195 <td><code>nullptr</code></td>
 196 <td>Declares a type-safe null pointer</td>
 197 <td><a href="http://en.cppreference.com/w/cpp/language/nullptr">
 198 nullptr</a></td>
 199 <td>Recommended for new code.
 200 <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/4mijeJHzxLg">Discussion thread</a>.
 201 <a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#0_and_nullptr/NULL">Google Style Guide</a>.
 202 Note: <code>std::nullptr_t</code> is a library feature and not available.
 203 </td>
 204 </tr>
 205
 206 <tr>
 207 <td>Override Specifier</td>
 208 <td><code>override</code></td>
 209 <td>Indicates that a class or function overrides a base implementation</td>
 210 <td><a href="http://en.cppreference.com/w/cpp/language/override">override Language Reference</a></td>
 211 <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>
 212 </tr>
 213
 214 <tr>
 215 <td>Range-Based For Loops</td>
 216 <td><code>for (<i>type</i> <i>var</i> : <i>range</i>)</code></td>
 217 <td>Facilitates a more concise syntax for iterating over the elements
 218 of a container (or a range of iterators) in a <code>for</code> loop</td>
 219 <td><a href="http://en.cppreference.com/w/cpp/language/range-for">
 220 Range-based for loop</a></td>
 221 <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>
 222 </tr>
 223
 224 <tr>
 225 <td>Standard Integers</td>
 226 <td>Typedefs within <code>&lt;stdint.h&gt;</code>
 227 and <code>&lt;inttypes&gt;</code></td>
 228 <td>Provides fixed-size integers independent of platforms</td>
 229 <td><a href="http://www.cplusplus.com/reference/cstdint/">
 230 &lt;stdint.h&gt; (cstdint)</a></td>
 231 <td>Already in common use in the codebase. Approved without discussion.</td>
 232 </tr>
 233
 234 <tr>
 235 <td>Static Assertions</td>
 236 <td><code>static_assert(<i>bool</i>, <i>string</i>)</code></td>
 237 <td>Tests compile-time conditions</td>
 238 <td><a href="http://en.cppreference.com/w/cpp/language/static_assert">Static Assertion</a></td>
 239 <td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/POISBQEhGzU">Discussion thread</a></td>
 240 </tr>
 241
 242 <tr>
 243 <td>Variadic Macros</td>
 244 <td><code>#define <i>MACRO</i>(...) <i>Impl</i>(<i>args</i>, __VA_ARGS__)</code></td>
 245 <td>Allows macros that accept a variable number of arguments</td>
 246 <td><a href="http://stackoverflow.com/questions/4786649/are-variadic-macros-nonstandard">
 247 Are Variadic macros nonstandard?</a></td>
 248 <td>Usage should be rare. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/sRx9j3CQqyA">Discussion thread</a></td>
 249 </tr>
 250
 251 <tr>
 252 <td>Variadic Templates</td>
 253 <td><code>template &lt;<i>typename</i> ... <i>arg</i>&gt;</code></td>
 254 <td>Allows templates that accept a variable number of arguments</td>
 255 <td><a href="http://en.cppreference.com/w/cpp/language/parameter_pack">
 256 Parameter pack</a></td>
 257 <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>
 258 </tr>
 259
 260 </tbody>
 261 </table>
 262
 263 <h2 id="blacklist">C++11 Blacklist (Disallowed and Banned Features)</h2>
 264
 265 <p>This section lists features that are not allowed to be used yet.
 266
 267 <h3 id="blacklist_banned">C++11 Banned Features</h3>
 268
 269 <p>This section lists C++11 features that are not allowed in the Chromium
 270 codebase.
 271 </p>
 272
 273 <table id="banned_list" class="unlined striped">
 274 <tbody>
 275
 276 <tr>
 277 <th style='width:240px;'>Feature or Library</th>
 278 <th style='width:240px;'>Snippet</th>
 279 <th style='width:240px;'>Description</th>
 280 <th style='width:240px;'>Documentation Link</th>
 281 <th style='width:240px;'>Notes</th>
 282 </tr>
 283
 284 <tr>
 285 <td>Constant Expressions</td>
 286 <td><code>constexpr</code></td>
 287 <td>Compile-time constant expressions</td>
 288 <td><a href="http://en.cppreference.com/w/cpp/language/constexpr">
 289 constexpr specifier</a></td>
 290 <td>Doesn't work in MSVS2013. Reevalute once it does. <a
 291 href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Use_of_constexpr">Google
 292 Style Guide on <code>constexpr</code></a></td>
 293 </tr>
 294
 295 <tr>
 296 <td>Explicit Conversion Operators</td>
 297 <td><code>explicit operator <i>type</i>() {
 298 <br />&nbsp;&nbsp;// code<br /> }</code></td>
 299 <td>Allows conversion operators that cannot be implicitly invoked</td>
 300 <td><a href="http://en.cppreference.com/w/cpp/language/explicit">
 301 explicit specifier</a></td>
 302 <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>
 303 </tr>
 304
 305 <tr>
 306 <td>Function Local Variable</td>
 307 <td><code>__func__</code></td>
 308 <td>Provides a local variable of the name of the enclosing
 309 function for logging purposes</td>
 310 <td><a href="http://www.informit.com/guides/content.aspx?g=cplusplus&amp;seqNum=338">
 311 The __func__ Predeclared Identifier is Coming to C++</a></td>
 312 <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>
 313 </tr>
 314
 315 <tr>
 316 <td>Inherited Constructors</td>
 317 <td><code>class Derived : Base {
 318 <br />&nbsp;&nbsp;using Base::Base;
 319 <br />};</code></td>
 320 <td>Allow derived classes to inherit constructors from base classes</td>
 321 <td><a href="http://en.cppreference.com/w/cpp/language/using_declaration">Using-declaration</a></td>
 322 <td>Doesn't work in MSVS2013. Reevaluate once it does. <a
 323 href="https://groups.google.com/a/chromium.org/d/msg/chromium-dev/BULzgIKZ-Ao/PLO7_GoVNvYJ">Discussion thread</a></td>
 324 </tr>
 325
 326 <tr>
 327 <td><code>long long</code> Type</td>
 328 <td><code>long long <i>var</i>= <i>value</i>;</code></td>
 329 <td>An integer of at least 64 bits</td>
 330 <td><a href="http://en.cppreference.com/w/cpp/language/types">
 331 Fundamental types</a></td>
 332 <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>
 333 </tr>
 334
 335 <tr>
 336 <td>Raw String Literals</td>
 337 <td><code>string <i>var</i>=R&quot;(<i>raw_string</i>)&quot;;</code></td>
 338 <td>Allows a string to be encoded without any escape
 339 sequences, easing parsing in regex expressions, for example</td>
 340 <td><a href="http://en.cppreference.com/w/cpp/language/string_literal">
 341 string literal</a></td>
 342 <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>
 343 </tr>
 344
 345 <tr>
 346 <td>Rvalue References (and Move Semantics)</td>
 347 <td><code>T(T&amp;&amp; t)</code> and <code>T&amp; operator=(T&amp;&amp; t)</code></td>
 348 <td>Reference that only binds to a temporary object</td>
 349 <td><a href="http://en.cppreference.com/w/cpp/language/references#Rvalue_references">
 350 Rvalue references</a></td>
 351 <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/chromium.org/d/topic/chromium-dev/UnRaORb4TSw">Discussion thread</a></td>
 352 </tr>
 353
 354 <tr>
 355 <td>(Uniform) Initialization Syntax</td>
 356 <td><code><i>type</i> <i>name</i> { [<i>value</i> ..., <i>value</i>]};</code></td>
 357 <td>Allows any object of primitive, aggregate or class
 358 type to be initialized using brace syntax</td>
 359 <td>TODO: documentation link</td>
 360 <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>
 361 </tr>
 362
 363 <tr>
 364 <td>UTF-16 and UTF-32 Support (16-Bit and 32-Bit Character Types)</td>
 365 <td><code>char16_t</code> and <code>char32_t</code></td>
 366 <td>Provides character types for handling 16-bit
 367 and 32-bit code units (useful for encoding
 368 UTF-16 and UTF-32 string data)</td>
 369 <td><a href="http://en.cppreference.com/w/cpp/language/types">
 370 Fundamental types</a></td>
 371 <td>Doesn't work in MSVS2013. Reevaluate once it does.  Non-UTF-8 text is
 372 banned by the
 373 <a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Non-ASCII_Characters">
 374 C++ Style Guide</a>. However, may be useful for
 375 consuming non-ASCII data. <a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/ME2kL7_Kvyk">Discussion thread</a></td>
 376 </tr>
 377
 378 <tr>
 379 <td>UTF-8, UTF-16, UTF-32 String Literals</td>
 380 <td><code>u8&quot;<i>string</i>&quot;, u&quot;<i>string</i>&quot;, U&quot;<i>string</i>&quot;</code></td>
 381 <td>Enforces UTF-8, UTF-16, UTF-32 encoding on all string literals</td>
 382 <td><a href="http://en.cppreference.com/w/cpp/language/string_literal">
 383 string literal</a></td>
 384 <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>
 385 </tr>
 386
 387 </tbody>
 388 </table>
 389
 390 <h3 id="blacklist_review">C++11 Features To Be Discussed</h3>
 391
 392 <p>The following C++ language features are currently disallowed.
 393 See the top of this page on how to propose moving a feature from this list
 394 into the allowed or banned sections. Note that not all of these features
 395 work in all our compilers yet.</p>
 396
 397 <table id="blacklist_review_list" class="unlined striped">
 398 <tbody>
 399
 400 <tr>
 401 <th style='width:240px;'>Feature</th>
 402 <th style='width:240px;'>Snippet</th>
 403 <th style='width:240px;'>Description</th>
 404 <th style='width:240px;'>Documentation Link</th>
 405 <th style='width:240px;'>Notes</th>
 406 </tr>
 407
 408 <tr>
 409 <td>Alignment Features</td>
 410 <td>
 411 <code>alignas</code> specifier,
 412 <code>std::alignment_of&lt;T&gt;</code>,
 413 <code>std::aligned_union&lt;Size, ...Types&gt;</code> and
 414 <code>std::max_align_t</code></td>
 415 <td>Object alignment</td>
 416 <td><a href="http://en.cppreference.com/w/cpp/types/alignment_of">std::alignment_of</a></td>
 417 <td></td>
 418 </tr>
 419
 420 <tr>
 421 <td>Attributes</td>
 422 <td><code>[[<i>attribute_name</i>]]</code></td>
 423 <td>Attaches properties to declarations that
 424 specific compiler implementations may use.</td>
 425 <td><a href="http://www.codesynthesis.com/~boris/blog/2012/04/18/cxx11-generalized-attributes/">
 426 C++11 generalized attributes</a></td>
 427 <td></td>
 428 </tr>
 429
 430 <tr>
 431 <td>Default Function Template Arguments</td>
 432 <td><code>template &lt;typename T = <i>type</i>&gt; <br />
 433 &nbsp;&nbsp;<i>type</i> <i>Function</i>(T <i>var</i>) {}</code></td>
 434 <td>Allow function templates, like classes, to have default arguments</td>
 435 <td><a href="http://stackoverflow.com/questions/2447458/default-template-arguments-for-function-templates">
 436 Default Template Arguments for Function Templates</a></td>
 437 <td></td>
 438 </tr>
 439
 440 <tr>
 441 <td>Exception Features</td>
 442 <td><code>noexcept</code>, <code>exception_ptr</code>,
 443 <code>current_exception()</code>, <code>rethrow_exception</code>,
 444 and <code>nested_exception</code></td>
 445 <td>Enhancements to exception throwing and handling</td>
 446 <td><a href="http://en.cppreference.com/w/cpp/error/exception">
 447 std::exception</a></td>
 448 <td>Exceptions are banned by the
 449 <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>
 450 </tr>
 451
 452 <tr>
 453 <td>Inline Namespaces</td>
 454 <td><code>inline</code></td>
 455 <td>Allows better versioning of namespaces</td>
 456 <td><a href="http://en.cppreference.com/w/cpp/language/namespace">Namespaces</a></td>
 457 <td>Unclear how it will work with components</td>
 458 </tr>
 459
 460 <tr>
 461 <td>Union Class Members</td>
 462 <td><code>union <i>name</i> { <i>class</i> <i>var</i>}</code></td>
 463 <td>Allows class type members</td>
 464 <td><a href="http://en.cppreference.com/w/cpp/language/union">
 465 Union declarations</a></td>
 466 <td></td>
 467 </tr>
 468
 469 <tr>
 470 <td>User-Defined Literals</td>
 471 <td><code><i>type</i> <i>var</i> = <i>literal_value</i>_<i>type</i></code></td>
 472 <td>Allows user-defined literal expressions</td>
 473 <td><a href="http://en.cppreference.com/w/cpp/language/user_literal">
 474 User-defined literals</a></td>
 475 <td></td>
 476 </tr>
 477
 478 </tbody>
 479 </table>
 480
 481 <h3 id="blacklist_stdlib">C++11 Standard Library features</h3>
 482
 483 <details>
 484
 485 <p><summary class="note">All C++11 <strong>Standard Library features are currently
 486 banned</strong>, because they are not supported on all of our toolchains yet.
 487 In particular, chromium/android is currently using STLport, and chromium/mac is
 488 currently using libstdc++4.2, which predate C++11.
 489 </summary></p>
 490
 491 <table id="banned_stdlib" class="unlined striped">
 492
 493 <tbody>
 494 <tr>
 495 <th style='width:240px;'>Feature</th>
 496 <th style='width:240px;'>Snippet</th>
 497 <th style='width:240px;'>Description</th>
 498 <th style='width:240px;'>Documentation Link</th>
 499 <th style='width:240px;'>Style Guide Usage</th>
 500 </tr>
 501
 502 <tr>
 503 <td>Address Retrieval</td>
 504 <td><code>std::addressof()</code></td>
 505 <td>Obtains the address of an object even with overloaded <code>operator&amp;</code></td>
 506 <td><a href="http://en.cppreference.com/w/cpp/memory/addressof">std::addressof</a></td>
 507 <td>Usage should be rare as
 508 <a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Operator_Overloading">
 509 Operator Overloading</a> is rare and <code>&amps;</code>
 510 should suffice in most cases. May be preferable
 511 over <code>&amps;</code> for performing object
 512 identity checks.</td>
 513 </tr>
 514
 515 <tr>
 516 <td>Aligned Storage</td>
 517 <td><code>std::aligned_storage&lt;Size, Align&gt;::type</code></td>
 518 <td>Declare uninitialized storage having a specified alignment.</td>
 519 <td><a href="http://en.cppreference.com/w/cpp/types/aligned_storage">std::aligned_storage</a></td>
 520 <td>Note: <code>std::aligned_storage</code> is allowed, but some other C++11
 521 alignment features are still disallowed.</td>
 522 </tr>
 523
 524 <tr>
 525 <td>Allocator Traits</td>
 526 <td><code>std::allocator_traits</code></td>
 527 <td>Provides an interface for accessing custom allocators</td>
 528 <td><a href="http://en.cppreference.com/w/cpp/memory/allocator_traits">
 529 std::allocator_traits</a></td>
 530 <td>Usage should be rare.</td>
 531 </tr>
 532
 533 <tr>
 534 <td>Atomics</td>
 535 <td><code>std::atomic</code> and others in <code>&lt;atomic&gt;</code></td>
 536 <td>Fine-grained atomic types and operations</td>
 537 <td><a href="http://en.cppreference.com/w/cpp/atomic">&lt;atomic&gt;</a></td>
 538 <td></td>
 539 </tr>
 540
 541 <tr>
 542 <td>Arrays</td>
 543 <td><code>std::array</code></td>
 544 <td>A fixed-size replacement for built-in arrays, with STL support</td>
 545 <td><a href="http://en.cppreference.com/w/cpp/container/array">
 546 std::array</a></td>
 547 <td></td>
 548 </tr>
 549
 550 <tr>
 551 <td>Begin and End Non-Member Functions</td>
 552 <td><code>std::begin()</code> and <code>std::end()</code></td>
 553 <td>Allows use of free functions on any container, including
 554 built-in arrays</td>
 555 <td><a href="http://en.cppreference.com/w/cpp/iterator/begin">
 556 std::begin</a> and
 557 <a href="http://en.cppreference.com/w/cpp/iterator/end">
 558 std::end</a></td>
 559 <td>Useful for built-in arrays.</td>
 560 </tr>
 561
 562 <tr>
 563 <td>Bind Operations</td>
 564 <td><code>std::bind(<i>function</i>, <i>args</i>, ...)</code></td>
 565 <td>Declares a function object bound to certain arguments</td>
 566 <td>TODO: documentation link</td>
 567 <td></td>
 568 </tr>
 569
 570 <tr>
 571 <td>C Floating-Point Environment</td>
 572 <td><code>&lt;cfenv&gt;</code></td>
 573 <td>Provides floating point status flags and control modes for C-compatible code</td>
 574 <td><a href="http://en.cppreference.com/w/cpp/header/cfenv">Standard library header &lt;cfenv&gt;</a></td>
 575 <td>Compilers do not support use</td>
 576 </tr>
 577
 578 <tr>
 579 <td>Chrono Library</td>
 580 <td><code>&lt;chrono&gt;</code></td>
 581 <td>Provides a standard date and time library</td>
 582 <td><a href="http://en.cppreference.com/w/cpp/chrono">Date and time utilities</a></td>
 583 <td></td>
 584 </tr>
 585
 586 <tr>
 587 <td>Complex Inverse Trigonometric and Hyperbolic Functions</td>
 588 <td>Functions within <code>&lt;complex&gt;</code></td>
 589 <td>Adds inverse trigonomentric and hyperbolic non-member functions to
 590 the <code>&lt;complex&gt;</code> library.</td>
 591 <td><a href="http://en.cppreference.com/w/cpp/numeric/complex">std::complex</a></td>
 592 <td></td>
 593 </tr>
 594
 595 <tr>
 596 <td>Conditional Type Selection</td>
 597 <td><code>std::enable_if</code> and <code>std::conditional</code></td>
 598 <td>Enables compile-time conditional type selection</td>
 599 <td><a href="http://en.cppreference.com/w/cpp/types/enable_if">
 600 std::enable_if</a> and
 601 <a href="http://en.cppreference.com/w/cpp/types/conditional">
 602 conditional</a></td>
 603 <td></td>
 604 </tr>
 605
 606 <tr>
 607 <td>Constant Iterator Methods on Containers</td>
 608 <td><code>std::cbegin()</code> and <code>std::cend()</code></td>
 609 <td>Enforces iteration methods that don't change container contents</td>
 610 <td>TODO: documentation link</td>
 611 <td></td>
 612 </tr>
 613
 614 <tr>
 615 <td>Construct Elements in Containers</td>
 616 <td><code>emplace()</code>,<code>emplace_back()</code>,
 617 <code>emplace_front()</code>, <code>emplace_hint()</code></td>
 618 <td>Constructs elements directly within a container without a copy
 619 or a move</td>
 620 <td>TODO: documentation link</td>
 621 <td>Use where element construction within a container
 622 is needed.</td>
 623 </tr>
 624
 625 <tr>
 626 <td>Container Compaction Functions</td>
 627 <td><code>std::vector::shrink_to_fit()</code>,
 628 <code>std::deque::shrink_to_fit()</code>, and
 629 <code>std::string::shrink_to_fit()</code></td>
 630 <td>Requests the removal of unused space
 631 in the container</td>
 632 <td><a href="http://en.cppreference.com/w/cpp/container/vector/shrink_to_fit">
 633 std::vector::shrink_to_fit</a>,
 634 <a href="http://en.cppreference.com/w/cpp/container/deque/shrink_to_fit">
 635 std::deque::shrink_to_fit</a>, and
 636 <a href="http://en.cppreference.com/w/cpp/string/basic_string/shrink_to_fit">
 637 std::basic_string::shrink_to_fit</a></td>
 638 <td></td>
 639 </tr>
 640
 641 <tr>
 642 <td>Date/Time String Formatting Specifiers</td>
 643 <td><code>std::strftime()</code></td>
 644 <td>Converts date and time information into a
 645 formatted string using new specifiers</td>
 646 <td><a href="http://en.cppreference.com/w/cpp/chrono/c/strftime">
 647 std::strftime</a></td>
 648 <td></td>
 649 </tr>
 650
 651 <tr>
 652 <td>Function Return Type Deduction</td>
 653 <td><code>std::result_of&lt;<i>Functor(ArgTypes...)</i>&gt;</code></td>
 654 <td>Extracts the return type from the type signature of
 655 a function call invocation at compile-time.</td>
 656 <td><a href="http://en.cppreference.com/w/cpp/types/result_of">
 657 std::result_of</a></td>
 658 <td>
 659 <a href="http://stackoverflow.com/questions/15486951/why-does-stdresult-of-take-an-unrelated-function-type-as-a-type-argument">
 660 Why does std::result_of take an (unrelated) function type as a type argument?
 661 </a></td>
 662 </tr>
 663
 664 <tr>
 665 <td>Function Objects</td>
 666 <td><code>std::function</code></td>
 667 <td>Wraps a standard polymorphic function</td>
 668 <td>TODO: documentation link</td>
 669 <td></td>
 670 </tr>
 671
 672 <tr>
 673 <td>Forward Lists</td>
 674 <td><code>std::forward_list</code></td>
 675 <td>Provides an efficient singly linked list</td>
 676 <td><a href="http://en.cppreference.com/w/cpp/container/forward_list">
 677 std::forward_list</a></td>
 678 <td></td>
 679 </tr>
 680
 681 <tr>
 682 <td>Gamma Natural Log</td>
 683 <td><code>std::lgamma()</code></td>
 684 <td>Computes the natural log of the gamma of a
 685 floating point value</td>
 686 <td><a href="http://en.cppreference.com/w/cpp/numeric/math/lgamma">
 687 std::lgamma</a></td>
 688 <td></td>
 689 </tr>
 690
 691 <tr>
 692 <td>Garbage Collection Features</td>
 693 <td><code>std::{un}declare_reachable()</code> and
 694 <code>std::{un}declare_no_pointers()</code></td>
 695 <td>Enables garbage collection implementations</td>
 696 <td><a href="http://en.cppreference.com/w/cpp/memory/gc/declare_reachable">
 697 std::declare_reachable</a>
 698 and <a href="http://en.cppreference.com/w/cpp/memory/gc/declare_no_pointers">
 699 std::declare_no_pointers</a></td>
 700 <td></td>
 701 </tr>
 702
 703 <tr>
 704 <td>Heap Validation</td>
 705 <td><code>std::is_heap()</code></td>
 706 <td>Checks whether an iterator range is in fact a heap</td>
 707 <td>TODO: documentation link</td>
 708 <td></td>
 709 </tr>
 710
 711 <tr>
 712 <td>Is Nan</td>
 713 <td><code>std::isnan()</code></td>
 714 <td>Determines if a floating point value is not-a-number</td>
 715 <td><a href="http://en.cppreference.com/w/cpp/numeric/math/isnan">std::isnan</a></td>
 716 <td></td>
 717 </tr>
 718
 719 <tr>
 720 <td>Iterator Operators</td>
 721 <td><code>std::next()</code> and <code>std::prev()</code></td>
 722 <td>Copies an iterator and increments or decrements the copy by
 723 some value</td>
 724 <td><a href="http://en.cppreference.com/w/cpp/iterator/next">std::next</a>
 725 and <a href="http://en.cppreference.com/w/cpp/iterator/prev">std::prev</a>
 726 </td>
 727 <td></td>
 728 </tr>
 729
 730 <tr>
 731 <td>Initializer Lists</td>
 732 <td><code>std::initializer_list&lt;T&gt;</code></td>
 733 <td>Allows containers to be initialized with aggregate elements</td>
 734 <td>TODO: documentation link</td>
 735 <td></td>
 736 </tr>
 737
 738 <tr>
 739 <td>Move Semantics</td>
 740 <td><code>std::move()</code></td>
 741 <td>Facilitates efficient move operations</td>
 742 <td><a href="http://en.cppreference.com/w/cpp/utility/move">
 743 <code>std::move</code> reference</a></td>
 744 <td></td>
 745 </tr>
 746
 747 <tr>
 748 <td>Pointer Traits Class Template</td>
 749 <td><code>std::pointer_traits</code></td>
 750 <td>Provides a standard way to access properties
 751 of pointers and pointer-like types</td>
 752 <td><a href="http://en.cppreference.com/w/cpp/memory/pointer_traits">
 753 std::pointer_traits</a></td>
 754 <td>Useful for determining the element type
 755 pointed at by a (possibly smart) pointer.</td>
 756 </tr>
 757
 758 <tr>
 759 <td>Random Number Generators</td>
 760 <td>Functions within <code>&lt;random&gt;</code></td>
 761 <td>Random number generation algorithms and utilities</td>
 762 <td><a href="http://en.cppreference.com/w/cpp/numeric/random">
 763 Pseudo-random number generation</a></td>
 764 <td></td>
 765 </tr>
 766
 767 <tr>
 768 <td>Ratio Template Class</td>
 769 <td><code>std::ratio&lt;<i>numerator</i>, <i>denominator</i>&gt;</code></td>
 770 <td>Provides compile-time rational numbers</td>
 771 <td>TODO: documentation link</td>
 772 <td></td>
 773 </tr>
 774
 775 <tr>
 776 <td>Reference Wrapper Classes</td>
 777 <td><code>std::reference_wrapper</code> and
 778 <code>std::ref()</code>, <code>std::cref()</code></td>
 779 <td>Allows you to wrap a reference within a standard
 780 object (and use those within containers)</td>
 781 <td><a href="http://www.informit.com/guides/content.aspx?g=cplusplus&amp;seqNum=217">
 782 Reference Wrappers</a></td>
 783 <td></td>
 784 </tr>
 785
 786 <tr>
 787 <td>Regex Library</td>
 788 <td><code>&lt;regex&gt;</code></td>
 789 <td>Provides a standard regular expressions library</td>
 790 <td><a href="http://en.cppreference.com/w/cpp/regex">Regular expressions library</a></td>
 791 <td></td>
 792 </tr>
 793
 794 <tr>
 795 <td>Shared Pointers</td>
 796 <td><code>std::shared_ptr</code></td>
 797 <td>Allows shared ownership of a pointer through reference counts</td>
 798 <td><a href="http://en.cppreference.com/w/cpp/memory/shared_ptr">std::shared_ptr</a></td>
 799 <td><a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Ownership_and_Smart_Pointers">
 800 Ownership and Smart Pointers</a></td>
 801 </tr>
 802
 803 <tr>
 804 <td>Soft Program Exits</td>
 805 <td><code>std::at_quick_exit()</code>
 806 and <code>std::quick_exit()</code></td>
 807 <td>Allows registration of functions to be called upon exit,
 808 allowing cleaner program exit than <code>abort()</code> or
 809 <code>exit</code></td>
 810 <td><a href="http://en.cppreference.com/w/cpp/utility/program/quick_exit">
 811 std:quick_exit</a></td>
 812 <td></td>
 813 </tr>
 814
 815 <tr>
 816 <td>String Direct Reference Functions</td>
 817 <td><code>std::string::front()</code> and <code>std::string::back()</code></td>
 818 <td>Returns a reference to the front or back of a string</td>
 819 <td><a href="http://en.cppreference.com/w/cpp/string/basic_string/front">
 820 std::basic_string::front</a> and
 821 <a href="http://en.cppreference.com/w/cpp/string/basic_string/back">
 822 std::basic_string::back</a></td>
 823 <td></td>
 824 </tr>
 825
 826 <tr>
 827 <td>String to Number Functions</td>
 828 <td><code>std::stoi()</code>, <code>std::stol()</code>,
 829 <code>std::stoul()</code>, <code>std::stoll</code>, <code>std::stoull()</code>,
 830 <code>std::stof()</code>, <code>std::stod()</code>, <code>std::stold()</code>,
 831 and <code>std::to_string()</code></td>
 832 <td>Converts strings to numbers</td>
 833 <td><a href="http://en.cppreference.com/w/cpp/string/basic_string/stol">
 834 std::stoi, std::stol, std::stoll</a>,
 835 <a href="http://en.cppreference.com/w/cpp/string/basic_string/stoul">
 836 std::stoul, std::stoull</a>, and
 837 <a href="http://en.cppreference.com/w/cpp/string/basic_string/stof">
 838 std::stof, std::stod, std::stold</a> </td>
 839 <td></td>
 840 </tr>
 841
 842 <tr>
 843 <td>STL Algorithms</td>
 844 <td>Functions within <code>&lt;algorithm&gt;</code>.</td>
 845 <td>Enhancements to the set of STL algorithms</td>
 846 <td>See the <a href="http://en.cppreference.com/w/cpp/algorithm">
 847 Algorithms library</a> for a complete list.</td>
 848 <td></td>
 849 </tr>
 850
 851 <tr>
 852 <td>System Errors</td>
 853 <td><code>&lt;system_error&gt;</code></td>
 854 <td>Provides a standard system error library</td>
 855 <td><a href="http://en.cppreference.com/w/cpp/error/system_error">std::system_error</a></td>
 856 <td></td>
 857 </tr>
 858
 859 <tr>
 860 <td>Trailing Return Types</td>
 861 <td><code>auto <i>function declaration</i> -> <i>return_type</i></code></td>
 862 <td>Allows trailing function return value syntax</td>
 863 <td><a href="http://en.cppreference.com/w/cpp/language/function">
 864 Declaring functions</a></td>
 865 <td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/OQyYSfH9m2M">Discussion thread</a></td>
 866 </tr>
 867
 868 <tr>
 869 <td>Thread Library</td>
 870 <td><code>&lt;thread&gt; support, including &lt;future&gt;,
 871 &lt;mutex&gt;, &lt;condition_variable&gt;</code></td>
 872 <td>Provides a standard mulitthreading library using <code>std::thread</code> and associates</td>
 873 <td><a href="http://en.cppreference.com/w/cpp/thread">Thread support library</a></td>
 874 <td></td>
 875 </tr>
 876
 877 <tr>
 878 <td>Tuples</td>
 879 <td><code>std::tuple</code></td>
 880 <td>A fixed-size ordered collection of values of mixed types</td>
 881 <td>TODO: documentation link</td>
 882 <td></td>
 883 </tr>
 884
 885 <tr>
 886 <td>Type-Generic Math Functions</td>
 887 <td>Functions within <code>&lt;ctgmath&gt;</code></td>
 888 <td>Provides a means to call real or complex functions
 889 based on the type of arguments</td>
 890 <td><a href="http://en.cppreference.com/w/cpp/header/ctgmath">
 891 Standard library header &lt;ctgmath&gt;</a></td>
 892 <td></td>
 893 </tr>
 894
 895 <tr>
 896 <td>Type Info Enhancements</td>
 897 <td><code>std::type_index</code> and <code>std::type_info::hash_code()</code></td>
 898 <td>Allows type information (most often within containers)
 899 that can be copied, assigned, or hashed</td>
 900 <td><a href="http://en.cppreference.com/w/cpp/types/type_index">
 901 std::type_index</a> and
 902 <a href="http://en.cppreference.com/w/cpp/types/type_info/hash_code">
 903 std::type_info::hash_code</a></td>
 904 <td><code>std::type_index</code> is a thin wrapper for
 905 <code>std::type_info</code>, allowing you to use it directly
 906 within both associative and unordered containers</td>
 907 </tr>
 908
 909 <tr>
 910 <td>Type Traits</td>
 911 <td>Class templates within <code>&lt;type_traits&gt;</code></td>
 912 <td>Allows compile-time inspection of the properties of types</td>
 913 <td><a href="http://en.cppreference.com/w/cpp/header/type_traits">
 914 Standard library header &lt;type_traits&gt;</a></td>
 915 <td></td>
 916 </tr>
 917
 918 <tr>
 919 <td>Unique Pointers</td>
 920 <td><code>std::unique_ptr&lt;<i>type</i>&gt;</code></td>
 921 <td>Defines a pointer with clear and unambiguous ownership</td>
 922 <td>TODO: documentation link</td>
 923 <td><a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Ownership_and_Smart_Pointers">
 924 Ownership and Smart Pointers</a></td>
 925 </tr>
 926
 927 <tr>
 928 <td>Unordered Associative Containers</td>
 929 <td><code>std::unordered_set</code>, <code>std::unordered_map</code>,
 930 <code>std::unordered_multiset</code>, and <code>std::unordered_multimap</code></td>
 931 <td>Allows efficient containers of key/value pairs</td>
 932 <td><a href="http://en.cppreference.com/w/cpp/container/unordered_map">std::unordered_map</a>
 933 and <a href="http://en.cppreference.com/w/cpp/container/unordered_set">std::unordered_set</a>
 934 </td>
 935 <td></td>
 936 </tr>
 937
 938 <tr>
 939 <td>Variadic Copy Macro</td>
 940 <td><code>va_copy(va_list <i>dest</i>, va_list <i>src</i>)</code></td>
 941 <td>Makes a copy of the variadic function arguments</td>
 942 <td></td>
 943 <td></td>
 944 </tr>
 945
 946 <tr>
 947 <td>Weak Pointers</td>
 948 <td><code>std::weak_ptr</code></td>
 949 <td>Allows a weak reference to a <code>std::shared_ptr</code></td>
 950 <td><a href="http://en.cppreference.com/w/cpp/memory/weak_ptr">
 951 std::weak_ptr</a></td>
 952 <td><a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Ownership_and_Smart_Pointers">
 953 Ownership and Smart Pointers</a></td>
 954 </tr>
 955
 956 <tr>
 957 <td>Wide String Support</td>
 958 <td><code>std::wstring_convert</code>,
 959 <code>std::wbuffer_convert</code>.
 960 <code>std::codecvt_utf8</code>, <code>std::codecvt_utf16</code>,
 961 and <code>std::codecvt_utf8_utf16</code></td>
 962 <td>Converts between string encodings</td>
 963 <td><a href="http://en.cppreference.com/w/cpp/locale/wstring_convert">
 964 std::wstring_convert</a>,
 965 <a href="http://en.cppreference.com/w/cpp/locale/wbuffer_convert">
 966 std::wbuffer_convert</a>,
 967 <a href="http://en.cppreference.com/w/cpp/locale/codecvt_utf8">
 968 std::codecvt_utf8</a>,
 969 <a href="http://en.cppreference.com/w/cpp/locale/codecvt_utf16">
 970 std::codecvt_utf16</a>, and
 971 <a href="http://en.cppreference.com/w/cpp/locale/codecvt_utf8_utf16">
 972 std::codecvt_utf8_utf16</a>
 973 </td>
 974 <td>Non-UTF-8 text is banned by the
 975 <a href="https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Non-ASCII_Characters">
 976 C++ Style Guide</a>. However, may be useful for
 977 consuming non-ASCII data.</td>
 978 </tr>
 979
 980 </tbody>
 981 </table>
 982
 983 </details>
 984
 985 </div>
 986 </body>
 987 </html>