Re: [Firebird-devel] Reference counters in API - was Re: Providers, yvalve, external engines and object lifecycle

[Adriano d. S. F. <adr...@gm...>]

On 30-03-2011 14:16, Daniel Rail wrote:
> X-UCS- Spam Mail 2
> 
> Hi,
> 
> Just to clarify a few things with relations to Delphi.
> 
> At March-30-11, 12:33 PM, Adriano dos Santos Fernandes wrote:
> 
>> On 30-03-2011 08:04, Vlad Khorsun wrote:
>>>
>>>     With Delphi you will just use IAttachment, without SmartPtr, as Delphi's "interface" have
>>> built-in compiler magic to work with reference counts.
>>>
>> AFAIK, this is not how it works.
> 
>> Delphi "interface" has nothing directly related with refcount.
> 
> Actually, Vlad is correct.
> Here's what is written in Delphi's help for IInterface:
> 
IInterface is a "interface" with three methods. This interface is
understood by the Delphi compiler and makes RAII works.

>   "IInterface introduces the QueryInterface method, which is useful
>   for discovering and using other interfaces implemented by the same
>   object. IInterface also introduces the reference counting methods,
>   _AddRef and _Release. The Delphi compiler automatically provides
>   calls to these methods when interfaces are used. The
>   TInterfacedObject class is provided as a base class for objects that
>   implement interfaces. Use of TInterfacedObject is not mandatory, but
>   will often be easier than designing an implementer class from
>   scratch."
> 
>> Refcount comes on when IInterface is used, but IInterface is about COM
>> (has queryInterface). I don't think you can make our interfaces to work
>> with IInterface, so you won't get RAII with Delphi and our interfaces.
> 
> You are correct when you say "Refcount comes on when IInterface is
> used".  But, Delphi's IInterface has nothing to do with COM, as I can
> use IInterface in an application, without ever using COM.  And, there
> are some that was able to implement RAII in Delphi, with the use of
> IInterface (I did a search on Google).
> 
And IInterface is incompatible with our Interface class, cause our don't
have QueryInterface.

So our Interface must be declared as:
Interface = interface
...
end;

and not:
Interface = interface(IInterface)
...
end;

Hence you can't make the Firebird objects uses Delphi's RAII.


Adriano