title: What is difference between "as" and "is" operator in Kotlin?
body: <p>In Java, I can write code like:</p>
  
  <pre><code>    void cast(A a)  {
      if(a  instanceof  Person)  {
          Person p = (Person) a;
      }
  }
  </code></pre>
  
  <p>In Kotlin, what should I do?
  Use <code>as</code> operator or <code>is</code> operator?</p>