title: Cannot use mutating member on immutable value of type 'String'
body: <p>I need to print <code>String</code> inside the <code>String</code> extensions. I am aware the addition of one <code>String</code> with another <code>String</code>. But, </p>
  
  <p>Why below code give me an error?</p>
  
  <p>Is it possible to solve this error with this way?</p>
  
  <p>If yes, How?</p>
  
  <p><strong>Code:</strong></p>
  
  <pre><code>extension String{
  
      func fruit(){
          //After some manipulation with self I need to print
          print("Apple".parent("Tree"))
          print("Tomato".parent("Plant"))
  
  
      }
  
      mutating func parent(_ word:String){
  
          self = self+" "+word
  
      }
  }
  </code></pre>
  
  <p><strong>Error :</strong></p>
  
  <blockquote>
    <p>Cannot use mutating member on immutable value of type 'String'</p>
  </blockquote>