Author: Tomas Rutkauskas

I'm trying to find a way to get the TObject reference from an IInterface object. I 
know that if the interface loses the reference the object will destroy but I've got 
a special need. The environment is based on interfaces but there is one component 
that can't use interfaces. So to work around it I assign the interface to a local 
variable, convert the interface to an object, call the component and when all is 
done get rid of the interface variable. Is this the right approach or can anything 
go wrong?

Answer:
1   
2   function GetImplementingObject(const I: IInterface): TObject;
3   const
4     AddByte = $04244483; {opcode for ADD DWORD PTR [ESP+4], Shortint}
5     AddLong = $04244481; {opcode for ADD DWORD PTR [ESP+4], Longint}
6   type
7     PAdjustSelfThunk = ^TAdjustSelfThunk;
8     TAdjustSelfThunk = packed record
9       case AddInstruction: longint of
10        AddByte: (AdjustmentByte: shortint);
11        AddLong: (AdjustmentLong: longint);
12    end;
13    PInterfaceMT = ^TInterfaceMT;
14    TInterfaceMT = packed record
15      QueryInterfaceThunk: PAdjustSelfThunk;
16    end;
17    TInterfaceRef = ^PInterfaceMT;
18  var
19    QueryInterfaceThunk: PAdjustSelfThunk;
20  begin
21    Result := Pointer(I);
22    if Assigned(Result) then
23    try
24      QueryInterfaceThunk := TInterfaceRef(I)^.QueryInterfaceThunk;
25      case QueryInterfaceThunk.AddInstruction of
26        AddByte: Inc(PChar(Result), QueryInterfaceThunk.AdjustmentByte);
27        AddLong: Inc(PChar(Result), QueryInterfaceThunk.AdjustmentLong);
28      else
29        Result := nil;
30      end;
31    except
32      Result := nil;
33    end;
34  end;