>goal</a></h2>
<p>合理完成调试...</p>
<h2 id="trace"><a class="header" href="#trace">trace</a></h2>
<p>有同学建议:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>if let Ok(exists) = conn.exists::&lt;bool, _&gt;(key).await {
    unimplemented!()
}
<span class="boring">}</span></code></pre></pre>
<p>于是开始探问:</p>
<blockquote>
<p>Q:</p>
</blockquote>
<p>if let Ok(exists) = conn.e