code: func (n *NamedStmt) Exec(arg interface{}) (sql.Result, error) {
  	args, err := bindAnyArgs(n.Params, arg, n.Stmt.Mapper)
  	if err != nil {
  		return *new(sql.Result), err
  	}
  	return n.Stmt.Exec(args...)
  }
docs: // Exec executes a named statement using the struct passed.
  // Any named placeholder parameters are replaced with fields from arg.