[fpc-devel] Considerations about observer [was: Free Pascal 2.6.2 rc1]

[luiz americo pereira camara]

2012/11/28  <michael.vancanneyt at wisa.be>:
>
>
> On Tue, 27 Nov 2012, luiz americo pereira camara wrote:
>
>> 2012/11/27 Michael Van Canneyt <michael at freepascal.org>:

>> 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 ?
>

I can post a simple example showing what i mean

I'll do today later. Currently i don't have access for a computer with fpc


>> 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...


In this case there's a gain.

The typecast would be done once when setting the parent property (IFPObserver)

Afterwards (setting children) would be no typecast, different as today


>
> During notification, we can gain speed by internally storing the interface.
>

OK. Seems here that we pacify the point of the reference count (not)
requirement to store the interface pointer

>
>> 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.

1) The change in code can be tedious but is simple. from Attach(MyObj)
to Attach(MyObj as IFPObserver)

2) I 'm assuming this as the first public release for wide test so the
best moment for such change

Luiz