Hack #7: Interface to Object [in The Delphi Magazine]

Due to the length and style, the following hack has been turned into a The Delphi Magazine article. IMO, this is simply the best Delphi magazine for professional developers and I highly recommend a subscription. Don't forget to get the Collection CD to read all my old articles :-) (in addition lots of other great articles too, of course).

Read the magazine article (update: in the October issue) to get the complete hack, explanations, history, the clean alternative, sample code and .NET comparison. As a teaser, here is the actual hack code:

function GetImplementingObject(const I: IInterface): TObject;

const  

 AddByte = $04244483; 

 AddLong = $04244481; 

type  

 PAdjustSelfThunk = ^TAdjustSelfThunk;  

 TAdjustSelfThunk = packed record    

   case AddInstruction: longint of      

     AddByte : (AdjustmentByte: shortint);      

     AddLong : (AdjustmentLong: longint);  

   end;  

 PInterfaceMT = ^TInterfaceMT;  

 TInterfaceMT = packed record    

   QueryInterfaceThunk: PAdjustSelfThunk;  

 end;  

 TInterfaceRef = ^PInterfaceMT;

var  

 QueryInterfaceThunk: PAdjustSelfThunk;

begin  

 Result := Pointer(I);  

 if Assigned(Result) then    

   try      

     QueryInterfaceThunk := TInterfaceRef(I)^.QueryInterfaceThunk;      

     case QueryInterfaceThunk.AddInstruction of        

       AddByte: Inc(PAnsiChar(Result), QueryInterfaceThunk.AdjustmentByte);        

       AddLong: Inc(PAnsiChar(Result), QueryInterfaceThunk.AdjustmentLong);         

      else    

       Result := nil;      

     end;    

   except      

     Result := nil;    

   end;

end;