PData = ^TData;
  TData = object
   private
    dtype:byte;
    procedure SetType(t:byte);
   public
    idata:THiInt;
    sdata:string;
    rdata:real;
    Next:PHI_Event;
    ldata:PData;
    property Data_type:byte read dtype write SetType;
  end;
...................
procedure TData.SetType;
begin
  ldata := nil;
  dtype := t;
end;

  ldata := nil;