 class="tmd-code-span">v</code> of type <code class="tmd-code-span">S</code>, we can use <code class="tmd-code-span">v.x</code> and <code class="tmd-code-span">v.y</code>, which are called selectors (or selector expressions), to represent the field values of <code class="tmd-code-span">v</code>. <code class="tmd-code-span">v</code> is called the receiver of the selectors.
</div>
<p></p>
<div class="tmd-usual">
Later, we call the dot <code class="tmd-code-span">.</code> in a selector as the property selectio