title: Tuple2 and tuple of two elements : what are their differences?
body: <p>In the following code, why type mismatch happened?</p>
  
  <pre><code>scala&gt; val lb = ListBuffer[Tuple2[Int, Int]]()
  lb: scala.collection.mutable.ListBuffer[(Int, Int)] = ListBuffer()
  
  scala&gt; lb += (1, 2)
  &lt;console&gt;:11: error: type mismatch;
   found   : Int(1)
   required: (Int, Int)
                lb += (1, 2)
                       ^
  
  scala&gt; lb += Tuple2(1, 2)
  res43: lb.type = ListBuffer((1,2))
  </code></pre>