On Thu, 24 Mar 2005 [EMAIL PROTECTED] wrote:
Quoting Michael Van Canneyt <[EMAIL PROTECTED]>:
On Wed, 23 Mar 2005 [EMAIL PROTECTED] wrote:
Quoting Marco van de Voort <[EMAIL PROTECTED]>:
On Tue, 22 Mar 2005, ml wrote:
// than one interface
a := (object as IA); // correct
b := (object as IB); // returns pointer to the first interface
vmt=IA
c := (object as IC); // returns pointer to the first interface
vmt=IA
// there's no way to do again it's like direct call to exception
obj := a; // returns pointer(obj) + 12 ???
This is nonsense. You cannot assign an interface to a class.
A class IMPLEMENTS an interface, it is not an interface.
Ok, its nonsense. I said it already works with my patch, but I guess you
know it better. So my example down there doesn't work (with patch). You
should know.
I (; can't ;) transfer from one interface to other back to object and to
3rd interface. I just imagine my results.
Tell me, what is
obj := a;
supposed to DO ? A class has a set of methods. Some of these methods form
the VMT of an interface. What your code does, is say
"don't use your VMT methods, use these instead' ?
Yes, exactly. I even provided test example at the bottom of my previous
message,
where I transfered from class to IA, back to class and then to ID. And called
ID.D; And it just works (this is also nice start for blind properties
implementation, which now also became possible, since original vmt is now
visible)
But, It should be used as
if (TObject(a).InheritedFrom(TSomeClass)) then begin
obj := TSomeClass(a); // note that here obj is declared as TSomeClass
// now safely use as this vmt
end;
if SupportsInterface(TObject(a), IB) then begin
ibvar := a; // declared ibvar: IB
// now safely use as this vmt
end;
in perfect world "is" would return InheritedFrom or SupportsInterface result and
not actual class check, if true then all needed operations are satisfied.
I can understand that 'is' should be able to check interfaces; this is a
useful patch.
I also understand what your code should do.
BUT I see some flaws in your design.
IA = Interface
procedure InitF;
end;
TA = class(TObject,IA)
F : TList;
Procedure InitF;
Procedure B;
end;
Procedure TA.InitF;
begin
F:=Tlist.Create;
end;
Procedure TA.B;
begin
F.Add(SomePointer);
end;
Var
A : TA;
C : IA;
begin
A:=TA.Create;
C:=SomeIA; // Get an IA interface from somewhere.
A:=C;
A.InitF; // <<--- Which InitF should be used ?
A.B; // Crash or not ?
end;
If TA.InitF is used, then B runs OK, but then A:=C has no meaning at all.
If the InitF from C is used, then F will not be initialized, and B will
fail.
Michael.
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