 additional
operator implementations for references. For example, for a user-defined
type <code>T</code> which is supposed to support addition, it is probably a good
idea to have both <code>T</code> and <code>&amp;T</code> implement the traits <a href="trait.Add.html"><code>Add&lt;T&gt;</code></a> and
<a href="trait.Add.html"><code>Add&lt;&amp;T&gt;</code></a> so that generic code can be written without unnecessary
cloning.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<