 context which is managed by the
        instance of <span class="emphasis"><em>asymmetric_coroutine&lt;&gt;::push_type</em></span>.
        The main execution context passes the strings to the <span class="emphasis"><em>coroutine-function</em></span>
        by calling <span class="emphasis"><em>asymmetric_coroutine&lt;&gt;::push_type::operator()</em></span>.
        An <span class="emphasis"><em>asymmetric_coroutine&lt;&gt;::pull_type</em></span> instance
        is automatically generated by the library 