libs/fiber/doc/html/fiber/synchronization/futures/packaged_task.html

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  25 <div class="section">
  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="fiber.synchronization.futures.packaged_task"></a><a name="class_packaged_task"></a><a class="link" href="packaged_task.html" title="Template packaged_task&lt;&gt;">Template
  28         <code class="computeroutput"><span class="identifier">packaged_task</span><span class="special">&lt;&gt;</span></code></a>
  29 </h4></div></div></div>
  30 <p>
  31           A <a class="link" href="packaged_task.html#class_packaged_task"><code class="computeroutput">packaged_task&lt;&gt;</code></a> wraps a callable target that
  32           returns a value so that the return value can be computed asynchronously.
  33         </p>
  34 <p>
  35           Conventional usage of <code class="computeroutput"><span class="identifier">packaged_task</span><span class="special">&lt;&gt;</span></code> is like this:
  36         </p>
  37 <div class="orderedlist"><ol class="orderedlist" type="1">
  38 <li class="listitem">
  39               Instantiate <code class="computeroutput"><span class="identifier">packaged_task</span><span class="special">&lt;&gt;</span></code> with template arguments matching
  40               the signature of the callable. Pass the callable to the <a class="link" href="packaged_task.html#packaged_task_packaged_task">constructor</a>.
  41             </li>
  42 <li class="listitem">
  43               Call <a class="link" href="packaged_task.html#packaged_task_get_future"><code class="computeroutput">packaged_task::get_future()</code></a> and capture
  44               the returned <a class="link" href="future.html#class_future"><code class="computeroutput">future&lt;&gt;</code></a> instance.
  45             </li>
  46 <li class="listitem">
  47               Launch a <a class="link" href="../../fiber_mgmt/fiber.html#class_fiber"><code class="computeroutput">fiber</code></a> to run the new <code class="computeroutput"><span class="identifier">packaged_task</span><span class="special">&lt;&gt;</span></code>, passing any arguments required
  48               by the original callable.
  49             </li>
  50 <li class="listitem">
  51               Call <a class="link" href="../../fiber_mgmt/fiber.html#fiber_detach"><code class="computeroutput">fiber::detach()</code></a> on the newly-launched <code class="computeroutput"><span class="identifier">fiber</span></code>.
  52             </li>
  53 <li class="listitem">
  54               At some later point, retrieve the result from the <code class="computeroutput"><span class="identifier">future</span><span class="special">&lt;&gt;</span></code>.
  55             </li>
  56 </ol></div>
  57 <p>
  58           This is, in fact, pretty much what <a class="link" href="future.html#fibers_async"><code class="computeroutput">fibers::async()</code></a>
  59 encapsulates.
  60         </p>
  61 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fiber</span><span class="special">/</span><span class="identifier">future</span><span class="special">/</span><span class="identifier">packaged_task</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  62
  63 <span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
  64 <span class="keyword">namespace</span> <span class="identifier">fibers</span> <span class="special">{</span>
  65
  66 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">R</span><span class="special">,</span> <span class="keyword">typename</span> <span class="special">...</span> <span class="identifier">Args</span> <span class="special">&gt;</span>
  67 <span class="keyword">class</span> <span class="identifier">packaged_task</span><span class="special">&lt;</span> <span class="identifier">R</span><span class="special">(</span> <span class="identifier">Args</span> <span class="special">...</span> <span class="special">)</span> <span class="special">&gt;</span> <span class="special">{</span>
  68 <span class="keyword">public</span><span class="special">:</span>
  69     <span class="identifier">packaged_task</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span>
  70
  71     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">&gt;</span>
  72     <span class="keyword">explicit</span> <span class="identifier">packaged_task</span><span class="special">(</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;);</span>
  73
  74     <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <a href="http://en.cppreference.com/w/cpp/concept/Allocator" target="_top"><code class="computeroutput"><span class="identifier">Allocator</span></code></a> <span class="special">&gt;</span>
  75     <span class="identifier">packaged_task</span><span class="special">(</span> <a href="http://en.cppreference.com/w/cpp/memory/allocator_arg_t" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span></code></a><span class="special">,</span> <span class="identifier">Allocator</span> <span class="keyword">const</span><span class="special">&amp;,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;);</span>
  76
  77     <span class="identifier">packaged_task</span><span class="special">(</span> <span class="identifier">packaged_task</span> <span class="special">&amp;&amp;)</span> <span class="keyword">noexcept</span><span class="special">;</span>
  78
  79     <span class="identifier">packaged_task</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">packaged_task</span> <span class="special">&amp;&amp;)</span> <span class="keyword">noexcept</span><span class="special">;</span>
  80
  81     <span class="identifier">packaged_task</span><span class="special">(</span> <span class="identifier">packaged_task</span> <span class="keyword">const</span><span class="special">&amp;)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
  82
  83     <span class="identifier">packaged_task</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">packaged_task</span> <span class="keyword">const</span><span class="special">&amp;)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
  84
  85     <span class="special">~</span><span class="identifier">packaged_task</span><span class="special">();</span>
  86
  87     <span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">packaged_task</span> <span class="special">&amp;)</span> <span class="keyword">noexcept</span><span class="special">;</span>
  88
  89     <span class="keyword">bool</span> <span class="identifier">valid</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
  90
  91     <span class="identifier">future</span><span class="special">&lt;</span> <span class="identifier">R</span> <span class="special">&gt;</span> <span class="identifier">get_future</span><span class="special">();</span>
  92
  93     <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">Args</span> <span class="special">...);</span>
  94
  95     <span class="keyword">void</span> <span class="identifier">reset</span><span class="special">();</span>
  96 <span class="special">};</span>
  97
  98 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Signature</span> <span class="special">&gt;</span>
  99 <span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">packaged_task</span><span class="special">&lt;</span> <span class="identifier">Signature</span> <span class="special">&gt;</span> <span class="special">&amp;,</span> <span class="identifier">packaged_task</span><span class="special">&lt;</span> <span class="identifier">Signature</span> <span class="special">&gt;</span> <span class="special">&amp;)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 100
 101 <span class="special">}}</span>
 102 </pre>
 103 <h6>
 104 <a name="fiber.synchronization.futures.packaged_task.h0"></a>
 105           <span class="phrase"><a name="fiber.synchronization.futures.packaged_task.default_constructor__code__phrase_role__identifier__packaged_task__phrase__phrase_role__special______phrase___code_"></a></span><a class="link" href="packaged_task.html#fiber.synchronization.futures.packaged_task.default_constructor__code__phrase_role__identifier__packaged_task__phrase__phrase_role__special______phrase___code_">Default
 106           constructor <code class="computeroutput"><span class="identifier">packaged_task</span><span class="special">()</span></code></a>
 107         </h6>
 108 <pre class="programlisting"><span class="identifier">packaged_task</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span>
 109 </pre>
 110 <div class="variablelist">
 111 <p class="title"><b></b></p>
 112 <dl class="variablelist">
 113 <dt><span class="term">Effects:</span></dt>
 114 <dd><p>
 115                 Constructs an object of class <code class="computeroutput"><span class="identifier">packaged_task</span></code>
 116                 with no <a class="link" href="future.html#shared_state">shared state</a>.
 117               </p></dd>
 118 <dt><span class="term">Throws:</span></dt>
 119 <dd><p>
 120                 Nothing.
 121               </p></dd>
 122 </dl>
 123 </div>
 124 <a name="packaged_task_packaged_task"></a><h6>
 125 <a name="fiber.synchronization.futures.packaged_task.h1"></a>
 126           <span class="phrase"><a name="fiber.synchronization.futures.packaged_task.templated_constructor__code__phrase_role__identifier__packaged_task__phrase__phrase_role__special______phrase___code_"></a></span><a class="link" href="packaged_task.html#fiber.synchronization.futures.packaged_task.templated_constructor__code__phrase_role__identifier__packaged_task__phrase__phrase_role__special______phrase___code_">Templated
 127           constructor <code class="computeroutput"><span class="identifier">packaged_task</span><span class="special">()</span></code></a>
 128         </h6>
 129 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">&gt;</span>
 130 <span class="keyword">explicit</span> <span class="identifier">packaged_task</span><span class="special">(</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">);</span>
 131
 132 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">typename</span> <a href="http://en.cppreference.com/w/cpp/concept/Allocator" target="_top"><code class="computeroutput"><span class="identifier">Allocator</span></code></a> <span class="special">&gt;</span>
 133 <span class="identifier">packaged_task</span><span class="special">(</span> <a href="http://en.cppreference.com/w/cpp/memory/allocator_arg_t" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span></code></a><span class="special">,</span> <span class="identifier">Allocator</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">alloc</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">fn</span><span class="special">);</span>
 134 </pre>
 135 <div class="variablelist">
 136 <p class="title"><b></b></p>
 137 <dl class="variablelist">
 138 <dt><span class="term">Effects:</span></dt>
 139 <dd><p>
 140                 Constructs an object of class <code class="computeroutput"><span class="identifier">packaged_task</span></code>
 141                 with a <a class="link" href="future.html#shared_state">shared state</a> and copies
 142                 or moves the callable target <code class="computeroutput"><span class="identifier">fn</span></code>
 143                 to internal storage.
 144               </p></dd>
 145 <dt><span class="term">Throws:</span></dt>
 146 <dd><p>
 147                 Exceptions caused by memory allocation.
 148               </p></dd>
 149 <dt><span class="term">Note:</span></dt>
 150 <dd><p>
 151                 The signature of <code class="computeroutput"><span class="identifier">Fn</span></code>
 152                 should have a return type convertible to <code class="computeroutput"><span class="identifier">R</span></code>.
 153               </p></dd>
 154 <dt><span class="term">See also:</span></dt>
 155 <dd><p>
 156                 <a href="http://en.cppreference.com/w/cpp/memory/allocator_arg_t" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_arg_t</span></code></a>
 157               </p></dd>
 158 </dl>
 159 </div>
 160 <h6>
 161 <a name="fiber.synchronization.futures.packaged_task.h2"></a>
 162           <span class="phrase"><a name="fiber.synchronization.futures.packaged_task.move_constructor"></a></span><a class="link" href="packaged_task.html#fiber.synchronization.futures.packaged_task.move_constructor">Move
 163           constructor</a>
 164         </h6>
 165 <pre class="programlisting"><span class="identifier">packaged_task</span><span class="special">(</span> <span class="identifier">packaged_task</span> <span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 166 </pre>
 167 <div class="variablelist">
 168 <p class="title"><b></b></p>
 169 <dl class="variablelist">
 170 <dt><span class="term">Effects:</span></dt>
 171 <dd><p>
 172                 Creates a packaged_task by moving the <a class="link" href="future.html#shared_state">shared
 173                 state</a> from <code class="computeroutput"><span class="identifier">other</span></code>.
 174               </p></dd>
 175 <dt><span class="term">Postcondition:</span></dt>
 176 <dd><p>
 177                 <code class="computeroutput"><span class="identifier">other</span></code> contains no
 178                 valid shared state.
 179               </p></dd>
 180 <dt><span class="term">Throws:</span></dt>
 181 <dd><p>
 182                 Nothing.
 183               </p></dd>
 184 </dl>
 185 </div>
 186 <h6>
 187 <a name="fiber.synchronization.futures.packaged_task.h3"></a>
 188           <span class="phrase"><a name="fiber.synchronization.futures.packaged_task.destructor"></a></span><a class="link" href="packaged_task.html#fiber.synchronization.futures.packaged_task.destructor">Destructor</a>
 189         </h6>
 190 <pre class="programlisting"><span class="special">~</span><span class="identifier">packaged_task</span><span class="special">();</span>
 191 </pre>
 192 <div class="variablelist">
 193 <p class="title"><b></b></p>
 194 <dl class="variablelist">
 195 <dt><span class="term">Effects:</span></dt>
 196 <dd><p>
 197                 Destroys <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 198                 and abandons the <a class="link" href="future.html#shared_state">shared state</a>
 199                 if shared state is ready; otherwise stores <code class="computeroutput"><span class="identifier">future_error</span></code>
 200                 with error condition <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">broken_promise</span></code>
 201                 as if by <a class="link" href="promise.html#promise_set_exception"><code class="computeroutput">promise::set_exception()</code></a>: the shared
 202                 state is set ready.
 203               </p></dd>
 204 </dl>
 205 </div>
 206 <p>
 207           </p>
 208 <h5>
 209 <a name="packaged_task_operator_assign_bridgehead"></a>
 210   <span class="phrase"><a name="packaged_task_operator_assign"></a></span>
 211   <a class="link" href="packaged_task.html#packaged_task_operator_assign">Member
 212           function <code class="computeroutput">operator=</code>()</a>
 213 </h5>
 214 <p>
 215         </p>
 216 <pre class="programlisting"><span class="identifier">packaged_task</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">packaged_task</span> <span class="special">&amp;&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 217 </pre>
 218 <div class="variablelist">
 219 <p class="title"><b></b></p>
 220 <dl class="variablelist">
 221 <dt><span class="term">Effects:</span></dt>
 222 <dd><p>
 223                 Transfers the ownership of <a class="link" href="future.html#shared_state">shared state</a>
 224                 to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
 225               </p></dd>
 226 <dt><span class="term">Postcondition:</span></dt>
 227 <dd><p>
 228                 <code class="computeroutput"><span class="identifier">other</span></code> contains no
 229                 valid shared state.
 230               </p></dd>
 231 <dt><span class="term">Throws:</span></dt>
 232 <dd><p>
 233                 Nothing.
 234               </p></dd>
 235 </dl>
 236 </div>
 237 <p>
 238           </p>
 239 <h5>
 240 <a name="packaged_task_swap_bridgehead"></a>
 241   <span class="phrase"><a name="packaged_task_swap"></a></span>
 242   <a class="link" href="packaged_task.html#packaged_task_swap">Member
 243           function <code class="computeroutput">swap</code>()</a>
 244 </h5>
 245 <p>
 246         </p>
 247 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">packaged_task</span> <span class="special">&amp;</span> <span class="identifier">other</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 248 </pre>
 249 <div class="variablelist">
 250 <p class="title"><b></b></p>
 251 <dl class="variablelist">
 252 <dt><span class="term">Effects:</span></dt>
 253 <dd><p>
 254                 Swaps the <a class="link" href="future.html#shared_state">shared state</a> between
 255                 other and <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
 256               </p></dd>
 257 <dt><span class="term">Throws:</span></dt>
 258 <dd><p>
 259                 Nothing.
 260               </p></dd>
 261 </dl>
 262 </div>
 263 <p>
 264           </p>
 265 <h5>
 266 <a name="packaged_task_valid_bridgehead"></a>
 267   <span class="phrase"><a name="packaged_task_valid"></a></span>
 268   <a class="link" href="packaged_task.html#packaged_task_valid">Member
 269           function <code class="computeroutput">valid</code>()</a>
 270 </h5>
 271 <p>
 272         </p>
 273 <pre class="programlisting"><span class="keyword">bool</span> <span class="identifier">valid</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
 274 </pre>
 275 <div class="variablelist">
 276 <p class="title"><b></b></p>
 277 <dl class="variablelist">
 278 <dt><span class="term">Effects:</span></dt>
 279 <dd><p>
 280                 Returns <code class="computeroutput"><span class="keyword">true</span></code> if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
 281                 contains a <a class="link" href="future.html#shared_state">shared state</a>.
 282               </p></dd>
 283 <dt><span class="term">Throws:</span></dt>
 284 <dd><p>
 285                 Nothing.
 286               </p></dd>
 287 </dl>
 288 </div>
 289 <p>
 290           </p>
 291 <h5>
 292 <a name="packaged_task_get_future_bridgehead"></a>
 293   <span class="phrase"><a name="packaged_task_get_future"></a></span>
 294   <a class="link" href="packaged_task.html#packaged_task_get_future">Member
 295           function <code class="computeroutput">get_future</code>()</a>
 296 </h5>
 297 <p>
 298         </p>
 299 <pre class="programlisting"><span class="identifier">future</span><span class="special">&lt;</span> <span class="identifier">R</span> <span class="special">&gt;</span> <span class="identifier">get_future</span><span class="special">();</span>
 300 </pre>
 301 <div class="variablelist">
 302 <p class="title"><b></b></p>
 303 <dl class="variablelist">
 304 <dt><span class="term">Returns:</span></dt>
 305 <dd><p>
 306                 A <a class="link" href="future.html#class_future"><code class="computeroutput">future&lt;&gt;</code></a> with the same <a class="link" href="future.html#shared_state">shared
 307                 state</a>.
 308               </p></dd>
 309 <dt><span class="term">Throws:</span></dt>
 310 <dd><p>
 311                 <code class="computeroutput"><span class="identifier">future_error</span></code> with
 312                 <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">future_already_retrieved</span></code> or <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">no_state</span></code>.
 313               </p></dd>
 314 </dl>
 315 </div>
 316 <p>
 317           </p>
 318 <h5>
 319 <a name="packaged_task_operator_apply_bridgehead"></a>
 320   <span class="phrase"><a name="packaged_task_operator_apply"></a></span>
 321   <a class="link" href="packaged_task.html#packaged_task_operator_apply">Member
 322           function <code class="computeroutput">operator()</code>()</a>
 323 </h5>
 324 <p>
 325         </p>
 326 <pre class="programlisting"><span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="identifier">Args</span> <span class="special">&amp;&amp;</span> <span class="special">...</span> <span class="identifier">args</span><span class="special">);</span>
 327 </pre>
 328 <div class="variablelist">
 329 <p class="title"><b></b></p>
 330 <dl class="variablelist">
 331 <dt><span class="term">Effects:</span></dt>
 332 <dd><p>
 333                 Invokes the stored callable target. Any exception thrown by the callable
 334                 target <code class="computeroutput"><span class="identifier">fn</span></code> is stored
 335                 in the <a class="link" href="future.html#shared_state">shared state</a> as if by
 336                 <a class="link" href="promise.html#promise_set_exception"><code class="computeroutput">promise::set_exception()</code></a>. Otherwise, the value
 337                 returned by <code class="computeroutput"><span class="identifier">fn</span></code> is
 338                 stored in the shared state as if by <a class="link" href="promise.html#promise_set_value"><code class="computeroutput">promise::set_value()</code></a>.
 339               </p></dd>
 340 <dt><span class="term">Throws:</span></dt>
 341 <dd><p>
 342                 <code class="computeroutput"><span class="identifier">future_error</span></code> with
 343                 <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">no_state</span></code>.
 344               </p></dd>
 345 </dl>
 346 </div>
 347 <p>
 348           </p>
 349 <h5>
 350 <a name="packaged_task_reset_bridgehead"></a>
 351   <span class="phrase"><a name="packaged_task_reset"></a></span>
 352   <a class="link" href="packaged_task.html#packaged_task_reset">Member
 353           function <code class="computeroutput">reset</code>()</a>
 354 </h5>
 355 <p>
 356         </p>
 357 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">reset</span><span class="special">();</span>
 358 </pre>
 359 <div class="variablelist">
 360 <p class="title"><b></b></p>
 361 <dl class="variablelist">
 362 <dt><span class="term">Effects:</span></dt>
 363 <dd><p>
 364                 Resets the <a class="link" href="future.html#shared_state">shared state</a> and abandons
 365                 the result of previous executions. A new shared state is constructed.
 366               </p></dd>
 367 <dt><span class="term">Throws:</span></dt>
 368 <dd><p>
 369                 <code class="computeroutput"><span class="identifier">future_error</span></code> with
 370                 <code class="computeroutput"><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">no_state</span></code>.
 371               </p></dd>
 372 </dl>
 373 </div>
 374 <p>
 375           </p>
 376 <h5>
 377 <a name="swap_for_packaged_task_bridgehead"></a>
 378   <span class="phrase"><a name="swap_for_packaged_task"></a></span>
 379   <a class="link" href="packaged_task.html#swap_for_packaged_task">Non-member
 380           function <code class="computeroutput">swap()</code></a>
 381 </h5>
 382 <p>
 383         </p>
 384 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Signature</span> <span class="special">&gt;</span>
 385 <span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">packaged_task</span><span class="special">&lt;</span> <span class="identifier">Signature</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">l</span><span class="special">,</span> <span class="identifier">packaged_task</span><span class="special">&lt;</span> <span class="identifier">Signature</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 386 </pre>
 387 <div class="variablelist">
 388 <p class="title"><b></b></p>
 389 <dl class="variablelist">
 390 <dt><span class="term">Effects:</span></dt>
 391 <dd><p>
 392                 Same as <code class="computeroutput"><span class="identifier">l</span><span class="special">.</span><span class="identifier">swap</span><span class="special">(</span>
 393                 <span class="identifier">r</span><span class="special">)</span></code>.
 394               </p></dd>
 395 </dl>
 396 </div>
 397 </div>
 398 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 399 <td align="left"></td>
 400 <td align="right"><div class="copyright-footer">Copyright &#169; 2013 Oliver Kowalke<p>
 401         Distributed under the Boost Software License, Version 1.0. (See accompanying
 402         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 403       </p>
 404 </div></td>
 405 </tr></table>
 406 <hr>
 407 <div class="spirit-nav">
 408 <a accesskey="p" href="promise.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../futures.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../fls.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
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