Confused about go syntax : <p>Little bit confused with this code. </p>

<pre><code>var _ QueryAppender = (*selectQuery)(nil)
</code></pre>

<p>I found this code in <a href="https://github.com/go-pg/pg/blob/master/orm/select.go" rel="nofollow noreferrer">pg-go</a>
 repository and don't know why <code>QueryAppender</code> declared that way. Please explain me what is the use cases when I should declare variables that way. </p>
