">)</span> <span class="o">-&gt;</span> <span class="kt">Bool</span> <span class="p">{</span>
    <span class="k">return</span> <span class="k">self</span> <span class="o">==</span> <span class="n">source</span>
<span class="p">}</span>
</code></pre>

<p>Therefore, you can simply:</p>
<pre class="highlight swift"><code><span class="kd">extension</span> <span class="kt">String</span><span class="p">:</span> <span class="kt">Differentiable</span> <span class="p">{}</span>
</code></pre>

<p>Calculate the diffs