rom context switch function enables
        to check if <span class="emphasis"><em>asymmetric_coroutine&lt;&gt;::pull_type</em></span>
        is valid after return from <span class="emphasis"><em>asymmetric_coroutine&lt;&gt;::pull_type::operator()</em></span>,
        e.g. <span class="emphasis"><em>asymmetric_coroutine&lt;&gt;::pull_type</em></span> has values
        and <span class="emphasis"><em>coroutine-function</em></span> has not terminated.
      </p>
<pre class="programlisting"><span class="ident