> On Nov 12, 2016, at 3:22 AM, Jonas Maebe <[email protected]> wrote:
>
> You're passing a class, not an object. Passing a class that implements an
> interface to a method that expects that interface should work fine.
> Converting a class instance to an interface that it implements is trivial and
> always works, it's doing the opposite that is hard and that requires specific
> support in the interface.
Here’s a better example of where this breaks. Yes casting does work to an
extent but breaks eventually down the chain when I lose the reference. Is there
anyway to get around this? Maybe I could store the reference from Supports
inside TMyObjectClass so I don’t need to call Supports again?
type
IMyInterface = interface
procedure DoSomething;
function GetObject: TObject;
end;
type
TMyObjectClass = class(IMyInterface)
procedure DoSomething;
function GetObject: TObject;
end;
var Obj: TMyObjectClass
ObjInt: IMyInterface;
Obj := TMyObject.Create;
ObjInt := Obj; // this works fine, casting to an interface
// Unit A only knows about IMyInterface so we pass
// the class cast as an interface (not sure what to call this)
DomeSomethingInUnitA(ObjInt);
// Unit A
var Obj: TObject;
Arr: TArray; // collection class the stores TObject
Arr := TArray.Create;
Obj := ObjInt.GetObject;
Arr.AddObject(Obj);
[do some stuff]
// here the problems start because TArray always returns TObject
// and I can’t cast TObject to IMyInterface even though the object
// stored in the array does in fact implement IMyInterface
ObjInt := IMyInterface(Arr.GetObject(0)); // error! but I need to get a
reference to IMyInterface from the array
// I have to use “as” or Supports here and it defeats the purpose
ObjInt := Arr.GetObject(0) as IMyInterface;
Regards,
Ryan Joseph
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