Question

In delphi 2009 I have a reference to a IInterface which I want to cast to the underlying TObject

Using TObject(IInterface) obviously doesn’t work in Delphi 2009 (it’s supposed to work in Delphi 2010 though)

My searches lead me to a function that should do the trick, but it doesn’t work for me, I get AV’s when I try to call methods on the returned object.

^{I can’t really modify the Classes and I know that this breaks OOP}

Answer 1

Instead of relying on Delphi’s internal object layout you could also have your objects implement another interface which would simply return the object. This, of course, only works if you have access to the source code of the objects to begin with, but you probably shouldn’t even use these hacks if you don’t have access the source code of the objects.

interface 

type
  IGetObject = interface
    function GetObject: TObject;
  end;

  TSomeClass = class(TInterfacedObject, IGetObject)
  public
    function GetObject: TObject;
  end;

implementation

function TSomeClass.GetObject: TObject;
begin
  Result := Self;
end;