d passed back to the caller
          through the future.
        </p>
<p>
          Where a handler signature has the form:
        </p>
<pre class="programlisting">void handler(boost::system::error_code ec);
</pre>
<p>
          the initiating function returns <code class="computeroutput">std::future&lt;void&gt;</code>. As
          above, an error is passed back in the future as a <code class="computeroutput">system_error</code>
          exception.
        </p>
<p>
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