I've talked with some friends of mine about the use of Interface base classes without reference counting in Delphi like this
type
TNoRefCount = class(TObject, IUnknown)
protected
function QueryInterface(const IID:TGUID; out Obj):HResult; stdcall;
function _AddRef: Integer; stdcall;
function _Release: Integer; stdcall;
end;
function TNoRefCount.QueryInterface(const IID:TGUID; out Obj): HResult;
begin
if GetInterface(IID, Obj) then
Result := 0
else
Result := Windows.E_NoInterface;
end;
function TNoRefCount._AddRef: Integer;
begin
Result := -1
end;
function TNoRefCount._Release: Integer;
begin
Result := -1
end;
We are all experiencing the same kind of problems:
1) there's no easy way to obtain a TObject from an interface (whereas there's no particular reason not to have it. A solution proposed was to implement an AsObject method in all the interfaces used.
2) there's no FreeAndNil function that would free the interface and the object instance.
It would be nice to be able to do something like this in an abstract factory: var MyRef: ISomeInterface; begin MyRef := SomeFactory.CreateObject as ISomeInterface; try ...use MyRef... finally MyRef.AsObject.Free; MyRef := nil; end; end;
Any Idea of a solution in free pascal?
From the fpc wiki (http://www.freepascal.org/wiki/wiki.phtml?title=Language_related_articles)
Interface type selection: The commandline switch -SI and the directive $interfaces (possible values: corba and com) allow you to choose the type of interfaces which has no parent. Interfaces with parent inherit the style from their parent regardless of the currently selected interface type.
* COM style interfaces work like Delphi interfaces: they inherit implicitly from IUnknown and they are reference counted.
* CORBA style interfaces are neither ref. counted nor do they inherit from IUnknown.
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