On Sep 3, 2009, at 11:47 AM, Jens Alfke wrote:
On Sep 3, 2009, at 11:40 AM, Scott Andrew wrote:
I could have sworn in either the apple docs (or one of the cocoa
books, maybe this board). I maybe thinking of the general rule that
you don't own the object until you retain it and its only valid or
the within the method that its recieved. My bad.
Here's an example of a return value that isn't autoreleased:
- (Foo*) foo {
static Foo* sharedFoo;
if (!sharedFoo) sharedFoo = [[Foo alloc] init];
return _sharedFoo;
}
Something similar is exactly what happens in the original code. On
Snow Leopard at least, both NSDictionary and NSArray have
optimizations for the "empty immutable collection" case. In both
classes there's a single shared instance that lives forever, so it
won't be destroyed even after every retain count that you are
responsible for has been released.
Try this:
{
NSDictionary *di = [[NSDictionary alloc] init];
NSArray *ar = [di allKeys];
NSDictionary *di2 = [[NSDictionary alloc] init];
NSArray *ar2 = [di allKeys];
NSLog(@"di %p, di2 %p", di, di2);
NSLog(@"ar %p, ar2 %p", ar, ar2);
}
You'll see that there's only one NSDictionary object and one NSArray
object, even though you called +alloc twice.
Then try your original test with a non-empty NSDictionary. You'll see
the memory management behave more like you expect. (Of course, `[ar
retainCount]` is likely to crash if called after `ar` is deallocated.)
--
Greg Parker gpar...@apple.com Runtime Wrangler
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