anchor.diff:   *                                                        *
    * hprose common unit for delphi.                         *
    *                                                        *
  - * LastModified: Nov 23, 2016                             *
  + * LastModified: Nov 27, 2016                             *
    * Author: Ma Bingyao <andot@hprose.com>                  *
    *                                                        *
   \**********************************************************/
  
positive.code:       Result := TObject(P^.VPointer);
        if not (Result is AClass) then Error(reInvalidCast);
      end
      else if P^.VType <> varNull then Error(reInvalidCast);
    except
      Error(reInvalidCast);
    end;
  
negative.code:     P := FindVarData(Value);
      if P^.VType = varObject then
        Result := TObject(P^.VPointer) is AClass
      else if (P^.VType <> varNull) and (P^.VType <> varEmpty) then
        Result := False;
    except
      Result := False;
  