title: Clarification on Swift line of dictionary and possible translation of map[x]!.append(product) to Kotlin
body: <p>I have a line in Swift that is:</p>
  <pre class="lang-swift prettyprint-override"><code>var map: [String:[String]] = [String:[String]]()
  map[x]!.append(product)
  </code></pre>
  <p>I am curious what the implementation <code>map[x]!.append(product)</code> is meant to be, additionally what an appropriate translation to Kotlin would be.</p>