Re: POC destructors? (was Re: bogus retain via NSEnumerator)

[Laurent Deniau]

Ben Golding wrote:
> In article <4088AA4F.DDE8A533@nospam.idiom.com>,
>  "John C. Randolph" <jcr@nospam.idiom.com> wrote:
>
>
> > Of course not.  I balance my retains and releases, I use -release when I
> > want to get rid of something immediately, and I use autorelease when
> > something else might want to keep the object in question around.  In
> > other words, I follow the published rules for retain/release.
>
>
> This discussion left me wondering how you can be sure when a program 
> using garbage collection can know when an object is finally released.  
>
> If I have a class that opens a file in it's init method, like:
>
>    @implementation MyFile
>
>    - (id)initWithPath:(char *)path
>    {
>       if ((self = [super init]) == nil)
>          return nil;
>
>       _fp = fopen(path, "r");
>
>       return self;
>    }
>
>    - (void)dealloc
>    {
>       fclose(_fp);
>       [super dealloc];
>    }
>   
>    @end
>
> How can I know when the -dealloc method is called by the garbage 
> collector?  If I create a lot of files using my class, how can I get POC 
> to call the destructor so I don't run out of file descriptors?

You can't (do not rely on finalization) but you should not need to do it...

-(void)dealloc
{
  [self close];
  [super dealloc];
}

-(int)close
{
  int err = 0;

  if (_fp != NULL)
    err = fclose(_fp), fp = NULL;

  return err;
}

This is a "well-know" design pattern in OO language when you use the 
paradigm "ressource acquisition is initialization".

> I had a look at the POC documentation and I couldn't see any 
> documentation on what conditions a destructor is called, or even if 
> there is a destructor method that's invoked when an object is destroyed.
>
> One advantage of the autorelease pool mechanism is that when I send a 
> -release message to an object and there are no other references, I know 
> that its -dealloc method will be called then and there.  There are 
> occasions when I want to defer the release of the objects because it 
> could impact the UI experience in which case I use -autorelease.  The 
> simple control that gives is quite something.
>
> So is there a way to force an object to call a destructor in POC or are 
> you at the dependent on the garbage collector?
>
>    Ben.

ld.