On 21.09.2014 21:09, Hans-Peter Diettrich wrote:
Sven Barth schrieb:
On 20.09.2014 13:42, Sven Barth wrote:
On 20.09.2014 13:11, Peter Popov wrote:
- to remedy this TObject is extended with non-virtual methods that
allow manual reference counting and would rely on the RTTI data I
mentioned (let's call the methods AddRef, Release, IsReferenceCounted
and RefCount for now, which can also be used to hook up the reference
counting of IUnknown interfaces);
I'd add a _RefCount field to TObject, regardless of whether it's really
used later; this will fix the field offset - just like the VMT reference
is fixed in TObject, but not in Object types. This will eliminate
problems with class helpers.
I've especially written that it's not part of *every* objects, because
people complained about the size increase for all instances.
make it safe:
=== code begin ===
function CreateObject: TObject;
begin
Result := TARCObject.Create;
Result.AddRef;
end;
=== code end ===
Here the compiler would always insert _AddRef, just like with
interfaces, eventually optimized (inlined?) like:
if Result._RefCounter <> -1 then
Result._AddRef; //or InterlockedIncrement(Result._RefCounter);
And that's another thing: people complained about having that reference
count overhead for *all* assignments.
- this now only leaves the problems of cycles; take this code:
=== code begin ===
type
TSomeClass = class(TARCObject)
Children: specialize TList<TSomeClass>;
Owner: TSomeClass;
constructor Create(aOwner: TSomeClass);
end;
constructor TSomeClass.Create(aOwner: TSomeClass);
begin
Children := specialize TList<TSomeClass>.Create;
Owner := aOwner;
if Assigned(Owner) then
Owner.Children.Add(Self);
end;
Here I'd prefer
Owner.AddChild(Self);
so that the Owner can implement any decent/appropriate child management
under the hood.
It. Was. Just. An. Example. To. Illustrate. The. Problem!
I would implement that differently as well, but there's *no* point to do
that inside an example that's supposed to be as simple as possible!
Regards,
Sven
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