title: Extension Property Kotlin
body: <p>I'm new in Kotlin
  I have a class Person with (name) and (age) property.
  How can I set the extension property for Person class like that</p>
  
  <pre><code>var Person.phone: Int
      get() = this.phone
      set(value) {this.phone = value}
  </code></pre>
  
  <p>How I can use setter in this case?
  Thank you.</p>