sealed abstract class LogRow
case class SemasioRow(x: String, y: Int) extends LogRow
case class TectonicRow(y: String, z: Float) extends LogRow

// Here comes the factory
object LogRow {
  def apply[T](s: String)(implicit m: Manifest[T]) = m match {
    case x: Manifest[SemasioRow] => new SemasioRow("xpto", 1)    // It's technically possible to make this a call to a companion SemasioRow object that decodes a string
    case x: Manifest[TectonicRow] => new TectonicRow("xpto", 2)
  }
}

object LogReader{
  def apply(filename: String): List[LogRow] = {
    List(LogRow[SemasioRow]("hello"))
  }
}