scala> collection.mutable.Buffer[Tuple2[Int, Int]]() += (1, 2)
<console>:8: error: type mismatch;
 found   : Int(1)
 required: (Int, Int)
              collection.mutable.Buffer[Tuple2[Int, Int]]() += (1, 2)
                                                                ^

scala> collection.mutable.Buffer[Tuple2[Int, Int]]() += ((1, 2))
res2: scala.collection.mutable.Buffer[(Int, Int)] = ArrayBuffer((1,2))

scala> Seq[Tuple2[Int, Int]]() :+ (1, 2)
res3: Seq[(Int, Int)] = List((1,2))