code: func (tx *Tx) Stmtx(stmt interface{}) *Stmt {
  	var s *sql.Stmt
  	switch v := stmt.(type) {
  	case Stmt:
  		s = v.Stmt
  	case *Stmt:
  		s = v.Stmt
  	case *sql.Stmt:
  		s = v
  	default:
  		panic(fmt.Sprintf("non-statement type %v passed to Stmtx", reflect.ValueOf(stmt).Type()))
  	}
  	return &Stmt{Stmt: tx.Stmt(s), Mapper: tx.Mapper}
  }
docs: // Stmtx returns a version of the prepared statement which runs within a transaction.  Provided
  // stmt can be either *sql.Stmt or *sqlx.Stmt.