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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.DescriptorService"></a><a class="link" href="DescriptorService.html" title="Descriptor service requirements">Descriptor service
requirements</a>
</h3></div></div></div>
<p>
A descriptor service must meet the requirements for an <a class="link" href="IoObjectService.html" title="I/O object service requirements">I/O
object service</a> with support for movability, as well as the additional
requirements listed below.
</p>
<p>
In the table below, <code class="computeroutput"><span class="identifier">X</span></code> denotes
a descriptor service class, <code class="computeroutput"><span class="identifier">a</span></code>
and <code class="computeroutput"><span class="identifier">ao</span></code> denote values of type
<code class="computeroutput"><span class="identifier">X</span></code>, <code class="computeroutput"><span class="identifier">b</span></code>
and <code class="computeroutput"><span class="identifier">c</span></code> denote values of type
<code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">implementation_type</span></code>, <code class="computeroutput"><span class="identifier">n</span></code>
denotes a value of type <code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">native_handle_type</span></code>,
<code class="computeroutput"><span class="identifier">ec</span></code> denotes a value of type
<code class="computeroutput"><span class="identifier">error_code</span></code>, <code class="computeroutput"><span class="identifier">i</span></code> denotes a value meeting <a class="link" href="IoControlCommand.html" title="I/O control command requirements"><code class="computeroutput"><span class="identifier">IoControlCommand</span></code></a> requirements, and
<code class="computeroutput"><span class="identifier">u</span></code> and <code class="computeroutput"><span class="identifier">v</span></code>
denote identifiers.
</p>
<div class="table">
<a name="boost_asio.reference.DescriptorService.t0"></a><p class="title"><b>Table 9. DescriptorService requirements</b></p>
<div class="table-contents"><table class="table" summary="DescriptorService requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
expression
</p>
</th>
<th>
<p>
return type
</p>
</th>
<th>
<p>
assertion/note<br> pre/post-condition
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">native_handle_type</span></code>
</p>
</td>
<td>
</td>
<td>
<p>
The implementation-defined native representation of a descriptor.
Must satisfy the requirements of <code class="computeroutput"><span class="identifier">CopyConstructible</span></code>
types (C++ Std, 20.1.3), and the requirements of <code class="computeroutput"><span class="identifier">Assignable</span></code> types (C++ Std, 23.1).
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">construct</span><span class="special">(</span><span class="identifier">b</span><span class="special">);</span></code>
</p>
</td>
<td>
</td>
<td>
<p>
From <a class="link" href="IoObjectService.html" title="I/O object service requirements">IoObjectService</a>
requirements.<br> post: <code class="computeroutput"><span class="special">!</span><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">destroy</span><span class="special">(</span><span class="identifier">b</span><span class="special">);</span></code>
</p>
</td>
<td>
</td>
<td>
<p>
From <a class="link" href="IoObjectService.html" title="I/O object service requirements">IoObjectService</a>
requirements. Implicitly cancels asynchronous operations, as if
by calling <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">close</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
<span class="identifier">ec</span><span class="special">)</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">move_construct</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">c</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
</td>
<td>
<p>
From <a class="link" href="IoObjectService.html" title="I/O object service requirements">IoObjectService</a>
requirements. The underlying native representation is moved from
<code class="computeroutput"><span class="identifier">c</span></code> to <code class="computeroutput"><span class="identifier">b</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">move_assign</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">ao</span><span class="special">,</span> <span class="identifier">c</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
</td>
<td>
<p>
From <a class="link" href="IoObjectService.html" title="I/O object service requirements">IoObjectService</a>
requirements. Implicitly cancels asynchronous operations associated
with <code class="computeroutput"><span class="identifier">b</span></code>, as if by
calling <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">close</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
<span class="identifier">ec</span><span class="special">)</span></code>.
Then the underlying native representation is moved from <code class="computeroutput"><span class="identifier">c</span></code> to <code class="computeroutput"><span class="identifier">b</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">assign</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">n</span><span class="special">,</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">error_code</span></code>
</p>
</td>
<td>
<p>
pre: <code class="computeroutput"><span class="special">!</span><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br> post: <code class="computeroutput"><span class="special">!!</span><span class="identifier">ec</span> <span class="special">||</span>
<span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">bool</span></code>
</p>
</td>
<td>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="keyword">const</span> <span class="identifier">X</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="identifier">a</span><span class="special">;</span>
<span class="keyword">const</span> <span class="identifier">X</span><span class="special">::</span><span class="identifier">implementation_type</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">b</span><span class="special">;</span>
<span class="identifier">u</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">bool</span></code>
</p>
</td>
<td>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">close</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">error_code</span></code>
</p>
</td>
<td>
<p>
If <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">()</span></code>
is true, causes any outstanding asynchronous operations to complete
as soon as possible. Handlers for cancelled operations shall be
passed the error code <code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">operation_aborted</span></code>.<br>
post: <code class="computeroutput"><span class="special">!</span><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">native_handle</span><span class="special">(</span><span class="identifier">b</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">native_handle_type</span></code>
</p>
</td>
<td>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">cancel</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">error_code</span></code>
</p>
</td>
<td>
<p>
pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br>
Causes any outstanding asynchronous operations to complete as soon
as possible. Handlers for cancelled operations shall be passed
the error code <code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">operation_aborted</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">.</span><span class="identifier">io_control</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span> <span class="identifier">i</span><span class="special">,</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">error_code</span></code>
</p>
</td>
<td>
<p>
pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.
</p>
</td>
</tr>
</tbody>
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