other four types, and vice versa, because the corresponding field names are different.
</div>
</li>
<li class="tmd-list-item">
<div class="tmd-usual">
two values of two different types among <code class="tmd-code-span">S1</code>, <code class="tmd-code-span">S2</code>, <code class="tmd-code-span">S3</code> and <code class="tmd-code-span">S4</code> can be converted to each other's type.
</div>
</li>
</ul>
<p></p>
<div class="tmd-usual">
In particular,
</div>
<ul class="tmd-list">
<li class="tmd-list-item">
<d