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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.reference.use_future_t"></a><a class="link" href="use_future_t.html" title="use_future_t">use_future_t</a>
</h3></div></div></div>
<p>
<a class="indexterm" name="asio.indexterm.use_future_t"></a>
</p>
<p>
A <a class="link" href="../overview/model/completion_tokens.html" title="Completion Tokens">completion token</a>
type that causes an asynchronous operation to return a future.
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">Allocator</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span><span class="special"><</span><span class="keyword">void</span><span class="special">>></span>
<span class="keyword">class</span> <span class="identifier">use_future_t</span>
</pre>
<h5>
<a name="asio.reference.use_future_t.h0"></a>
<span><a name="asio.reference.use_future_t.types"></a></span><a class="link" href="use_future_t.html#asio.reference.use_future_t.types">Types</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
<a class="link" href="use_future_t/allocator_type.html" title="use_future_t::allocator_type"><span class="bold"><strong>allocator_type</strong></span></a>
</p>
</td>
<td>
<p>
The allocator type. The allocator is used when constructing the
std::promise object for a given asynchronous operation.
</p>
</td>
</tr></tbody>
</table></div>
<h5>
<a name="asio.reference.use_future_t.h1"></a>
<span><a name="asio.reference.use_future_t.member_functions"></a></span><a class="link" href="use_future_t.html#asio.reference.use_future_t.member_functions">Member
Functions</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
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<th>
<p>
Name
</p>
</th>
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<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="use_future_t/get_allocator.html" title="use_future_t::get_allocator"><span class="bold"><strong>get_allocator</strong></span></a>
</p>
</td>
<td>
<p>
Obtain allocator.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="use_future_t/operator_lp__rp_.html" title="use_future_t::operator()"><span class="bold"><strong>operator()</strong></span></a>
</p>
</td>
<td>
<p>
Wrap a function object in a packaged task.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="use_future_t/operator_lb__rb_.html" title="use_future_t::operator[]"><span class="bold"><strong>operator[]</strong></span></a>
</p>
</td>
<td>
<p>
(Deprecated: Use rebind().) Specify an alternate allocator.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="use_future_t/rebind.html" title="use_future_t::rebind"><span class="bold"><strong>rebind</strong></span></a>
</p>
</td>
<td>
<p>
Specify an alternate allocator.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="use_future_t/use_future_t.html" title="use_future_t::use_future_t"><span class="bold"><strong>use_future_t</strong></span></a> <span class="silver">[constructor]</span>
</p>
</td>
<td>
<p>
Construct using default-constructed allocator. <br> <span class="silver"> —</span><br> Construct
using specified allocator.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
The <a class="link" href="use_future_t.html" title="use_future_t"><code class="computeroutput"><span class="identifier">use_future_t</span></code></a>
class is a completion token type that is used to indicate that an asynchronous
operation should return a std::future object. A <a class="link" href="use_future_t.html" title="use_future_t"><code class="computeroutput"><span class="identifier">use_future_t</span></code></a> object may be passed
as a completion token to an asynchronous operation, typically using the special
value <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span></code>. For example:
</p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">my_future</span>
<span class="special">=</span> <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span><span class="special">);</span>
</pre>
<p>
The initiating function (async_read_some in the above example) returns a
future that will receive the result of the operation. If the operation completes
with an <a class="link" href="error_code.html" title="error_code"><code class="computeroutput"><span class="identifier">error_code</span></code></a>
indicating failure, it is converted into a <a class="link" href="system_error.html" title="system_error"><code class="computeroutput"><span class="identifier">system_error</span></code></a> and passed back to
the caller via the future.
</p>
<h5>
<a name="asio.reference.use_future_t.h2"></a>
<span><a name="asio.reference.use_future_t.requirements"></a></span><a class="link" href="use_future_t.html#asio.reference.use_future_t.requirements">Requirements</a>
</h5>
<p>
<span class="emphasis"><em>Header: </em></span><code class="literal">asio/use_future.hpp</code>
</p>
<p>
<span class="emphasis"><em>Convenience header: </em></span><code class="literal">asio.hpp</code>
</p>
</div>
<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
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