On Tue, 27 Nov 2012, luiz americo pereira camara wrote:
2012/11/27 Michael Van Canneyt <mich...@freepascal.org>:
On Tue, 27 Nov 2012, luiz americo pereira camara wrote:
Hi, i requested a change to observer interface with some
considerations in http://bugs.freepascal.org/view.php?id=23394
It will not happen.
If you want to pass around interfaces safely, then you need to implement
them as
descendents of IUnknown to maintain reference counts. They are implemented
as CORBA interfaces exactly to avoid the overhead of IUnknown.
The consequence is that you must pass around the objects themselves.
I don't see the point.
It would be true if the IFPObserved (e.g., TPersistent) takes
ownership of the attached observers. That is not the case.
Currently, in the observer feature, there's no difference between
plain TObject and corba interface (IFPObserver) regarding the life
cycle management.
Correct.
Both there are no guarantees that they will still be alive when accessed.
The current approach limits the programmer flexibility and adds
unnecessary overhead.
As practical example take a LCL Form that is supposed to be observed.
It takes an Observer property and attach it to certain child controls
(TEdit etc)
1) Currently i'm forced to declare as the Observer property as an
TObject. If i declare Observer property as IFPObserver i cannot attach
to children controls.
I do not understand this ?
2) Each time i attach to a child control this Observer property will
be queried to see if implements IFPObserver (but we already know that
it implements, we already checked !!!)
You only gain speed when notifying. When calling FPOAttachAbserver or
FPODetachAbserver, you would need to typecast some object anyway if we
would change the interface, so there is no speed gain there...
During notification, we can gain speed by internally storing the interface.
So, i keep my points. Even because is not a big change with easy
implementation that will fix the above issues.
It IS a big change. There is production code out there that uses this,
and this is an incompatible change.
I can change the internals so speed is gained during notifyobservers,
but I do not see sufficient reasons to change the interface and introduce an
incompatibility.
Michael.
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