Re: ObjectPtrT question

On Dec 21, 2004, at 6:35 AM, Jess.Morecroft@xxxxxxx wrote:

> Hi,
>
> I'm writing a custom appender for log4cxx, and have a few questions 
> about the Object/ObjectImpl/ObjectPtrT classes.....Basically I'm going 
> to code a number of classes that extend ObjectImpl, to make use of the 
> ObjectPtrT "smart pointer" template and the Java-inspired threading 
> methods, wait, notifiy, notifyAll (and I notice you have a semaphore 
> imp...nice).

Actually, I've been removing the Java-inspired threading methods from 
the underlying Object interface in the APR rework.  Only a few classes 
used the constructs but it required every object to carry around 
mutexes and trying to precisely reproduce the Java threading semantics 
is a non-trivial task.


> My question is a very general one.....what are the general rules of 
> thumb you've been using when extending the ObjectImpl class?.... I've 
> noticed the object macros (eg. casting ones), and will be including 
> them in the declarations and implementations for my descendant 
> classes. Can't say I'm entirely sure of the purpose of the cast method 
> defined by the object class and implemented by the macros....is this 
> just supposed to be a safe way of dynamically down-casting an 
> object?....if so why was this method chosen in favour of the builtin 
> dynamic_cast mechanism?...anyway, my C++ is good, but not exceptional 
> (yet :-) ), so please excuse me if I've missed something here.

I can only speculate on the motivation since I wasn't in the project 
when the code was originally written.  The casting mechanism is an 
attempt to do support safe down-casting and could have been written 
using RTTI.  I assume that RTTI was avoided since compiler support 
varies and use of RTTI may have required code that used log4cxx be 
compiled with RTTI enabled.  It might be good to see if downcasting is 
actually used within log4cxx, if not maybe those macros could be 
stubbed out.