How to create a GUID at runtime

uses
  ComObj, ActiveX;

function CreateGuid: string;
var
  ID: TGUID;
begin
  Result := '';
  if CoCreateGuid(ID) = S_OK then
    Result := GUIDToString(ID);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Edit1.Text := CreateGuid;
  // or: Edit1.Text := CreateClassID
end;