[fpc-devel] {$Interfaces Corba} and TInterfacedObject

[Joao Morais]

Graeme Geldenhuys wrote:
> So what do I use to create interfaces and classes that implement interfaces?
> Which declaration style do I use?  Or doesn't it make a difference?
> 
> type
>   ICommand = interface(IInterface)
>   vs
>   ICommand = interface(IUnkown)

They are exactly the same ? (D<=5 and D>=6 compatibility)

>   ICommand = interface

Under $interfaces com, interface = interface(iunknown)

> Now for created classes that implement those interfaces. What base
> object do I use?
> 
> type
>   TCommandClass = class(TInterfacedObject, ICommand)
>   vs
>   TCommandClass = class(TSomeCustomNonReferenceCountedClass, ICommand)

I am using my own classes that implement _addref, _release and QueryIntf 
and am very happy with them. I do use refcounting where I want 
(everywhere btw) and don't destroy the instance where I don't want.

You will want to use TInterfacedObject class if you:

1. Want refcounting;
2. Don't want to destroy the instance if the refcount <> 0 (the object 
will raise an exception);
3. Don't need to descend from another class.
4. Will take care with circular references.

Otherwise you will need to create your own class and:

1. implement _addref, _release and QueryIntf if using com interfaces;
2. do nothing if using corba interfaces (I have no idea how an interface 
is "queried" here).

> I can't imagine that usig Corba style interfaces that I'm allowed to
> use TInterfacedObject as a based class, because TInterfacedObject
> implements reference counting.  Is there some other base class I'm
> supposed to use with Corba style interfaces?

Any class. Afaik corba interfaces doesn't implement a method ?

> Does FPC have a Non-Reference counted base class already?  It's quite
> simple to implement you own, but is stupid if FPC doesn't already have
> one.

Err... a class doesn't have refcount, just start with TObject or a 
descendant.

> Also, do I have to specify {$Interfaces Corba} in every unit I have,
> or is it only needed in the using that defines the interface itself?

You need. See eg MSE units.

> Basically, is that compiler setting unit based or project (global)
> based.  Why I ask, is because {$mode xxx} is unit based, not global
> across my whole project.  So can I mix Reference counted and
> Non-Reference counted interface styles in the same project?

Any compiler directive is unit based. The unit where you declared the 
interface is what will count here.

> I found find any help referencing these issues.... The help topics on
> interfaces and $Interfaces styles are very vague.

Not vague, they was straight to the point imo.

--
Joao Morais