Re: Memory Management Mismanaged
Re: Memory Management Mismanaged
- Subject: Re: Memory Management Mismanaged
- From: Marcel Weiher <email@hidden>
- Date: Thu, 8 May 2003 12:00:30 +0200
- Mark and sweep garbage collection does not work well with
distributed
objects. Reference counting does.
<SNIP>Most excellent reply</SNIP>
Agreed
And there you have it.
As one who recently had the "Aha!" experience with Cocoa memory
management,
I have a piece of advice for anyone struggling with it...
When you create a new class (say, MyFoo), also create a class method to
allocate new instances, as many of the Cocoa classes do (e.g.,
[NSDictionary dictionary]).
Yes, this is excellent advice.
For example,
+ (MyFoo*) myFoo
{
MyFoo* aFoo = [[[myFoo alloc] init] autorelease];
return aFoo;
}
Three minor nits:
1. Don't use a static return type, this will break for subclasses. Use
id
2. For the same reason, use 'self' to refer to the current class
3. I don't think the temporary variable is buying you anything here, so:
+myFoo
{
return [[[self alloc] init] autorelease];
}
Now you can say...
MyFoo* newFoo = [MyFoo myFoo]; // this guy will die in the next
event cycle
More accurate and simpler: // I am not responsible for releasing
this guy.
So, if you want to keep the object longer than one event cycle, do this
instead:
MyFoo* newFoo = [[MyFoo myFoo] retain];
Possibly easier:
[self setFoo:[MyFoo myFoo]];
It's much better, IMHO, to create temporary objects by default, since
that
eliminates a large number of potential leaks (and it was leaks that
lead me
to the "Aha!" moment), and you'll soon find out which objects need to
be
retained, since you'll get a crash if try to access one which wasn't.
Yes. Although I don't get many crashes, because I uses accessors for
all instance variable access and only instance variables stick around.
So memory management has almost completely left the picture.
Actualy, I was amazed at how much simpler the code got after I adopted
this
approach. In my app, I was generating a lot of temporary objects
simply to
pass around as values from one method to another, plus a few instances
which were suppposed to stay alive for the lifespan of the document.
Long
story short, things got a lot better :o)
Yup. Couldn't agree more with what Duncan is saying, except I would
say it can get even simpler... ;-)
Marcel
--
Marcel Weiher Metaobject Software Technologies
email@hidden www.metaobject.com
Metaprogramming for the Graphic Arts. HOM, IDEAs, MetaAd etc.
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