What kind of leaks does Objective-C's automatic reference counting (in Xcode 4.2) not prevent/minimize?

The primary memory-related problem you'll still need to be aware of is retain cycles. This occurs when one object has a strong pointer to another, but the target object has a strong pointer back to the original. Even when all other references to these objects are removed, they still will hold on to one another and will not be released.

This can also happen indirectly, by a chain of objects that might have the last one in the chain referring back to an earlier object It is for this reason that the unsafe_unretained and weak ownership qualifiers exist. The former will not retain any object it points to, but leaves open the possibility of that object going away and it pointing to bad memory, whereas the latter doesn't retain the object and automatically sets itself to nil when its target is deallocated. Of the two weak is generally preferred on platforms that support it You would use these qualifiers for things like delegates, where you don't want the object to retain its delegate and potentially lead to a cycle Of course, there are several other less frequent, but still potentially problematic cases, which the published specification goes into in detail Much of the new behavior, based on keeping objects around as long as there is a strong pointer to them, is very similar to garbage collection on the Mac.

However, the technical underpinnings are very different. Rather than having a garbage collector process that runs at regular intervals to clean up objects no longer being pointed to, this style of memory management relies on the rigid retain / release rules we all need to obey in Objective-C ARC simply takes the repetitive memory management tasks we've had to do for years and offloads them to the compiler so we never have to worry about them again. This way, you don't have the halting problems or sawtooth memory profiles experienced on garbage collected platforms.

I've experienced both of these in my garbage collected Mac applications, and am eager to see how they behave under ARC For more on garbage collection vs. ARC, see this very interesting response by Chris Lattner on the Objective-C mailing list where he lists many advantages of ARC over Objective-C 2.0 garbage collection. I've run into several of the GC issues he describes.

The primary memory-related problem you'll still need to be aware of is retain cycles. This occurs when one object has a strong pointer to another, but the target object has a strong pointer back to the original. Even when all other references to these objects are removed, they still will hold on to one another and will not be released.

This can also happen indirectly, by a chain of objects that might have the last one in the chain referring back to an earlier object. It is for this reason that the __unsafe_unretained and __weak ownership qualifiers exist. The former will not retain any object it points to, but leaves open the possibility of that object going away and it pointing to bad memory, whereas the latter doesn't retain the object and automatically sets itself to nil when its target is deallocated.

Of the two, __weak is generally preferred on platforms that support it. You would use these qualifiers for things like delegates, where you don't want the object to retain its delegate and potentially lead to a cycle. Of course, there are several other less frequent, but still potentially problematic cases, which the published specification goes into in detail.

Much of the new behavior, based on keeping objects around as long as there is a strong pointer to them, is very similar to garbage collection on the Mac. However, the technical underpinnings are very different. Rather than having a garbage collector process that runs at regular intervals to clean up objects no longer being pointed to, this style of memory management relies on the rigid retain / release rules we all need to obey in Objective-C.

ARC simply takes the repetitive memory management tasks we've had to do for years and offloads them to the compiler so we never have to worry about them again. This way, you don't have the halting problems or sawtooth memory profiles experienced on garbage collected platforms. I've experienced both of these in my garbage collected Mac applications, and am eager to see how they behave under ARC.

For more on garbage collection vs. ARC, see this very interesting response by Chris Lattner on the Objective-C mailing list, where he lists many advantages of ARC over Objective-C 2.0 garbage collection. I've run into several of the GC issues he describes.

Theoretically, ARC should take care of 100% of normally allocated and released objects. Because of the new compiler you often don't even need an autoreleasepool (@autoreleasepool) where you did before. They did specifically mention that if you retain/released objects based upon the retain counts of other objects (really confusing cases that nobody should ever use) then the compiler wouldn't understand how to fix it.

When it runs into issues it will ask for your intervention so that assuming your corrections are good, you can rely on the ARC code 100% of the time.

A freckle is a tan color spot on the surface of your skin. They usually appear after exposure to the sun in fair skinned people. Two different types of freckles are simple and sunburn.

You can find more information here: medicinenet.com/freckles/article.htm#1wh....

Hair Rebonding is a chemical hair treatment that makes your hair straight, sleek and shiny. It is a permanent and expensive procedure. Prices for the treatment may vary across many different salons, this being due to products used, service, your hair type and post treatment care.

Each type of hair has a natural bond. Curly or wavy, are the result of natural bonds that give the hair its physical quality. The cream softener or relaxant used in the rebonding treatment breaks the hair structure.

Then a simple neutralizer bonds the structure again and makes hair straight. In simpler terms the rebonding treatment changes your natural hair structure and then also restructures it. Once you have gotten you hair completely straightened you will then have to actually touch up the new growth every three months, six months or a year, depending on how fast your hair actually grows on its own.

Hair rebonding is a chemical treatment that straightens your hair. It's different from regular straightening way. This require of ironing the hair, so once all hair are straightened, they apply this neutralizer.

The results of rebonding is more straigther, and shinier. It looks like your hair is ironed everyday. In asian contry, it's not too expensive, you can actually have a long hair rebonded for $30 to $50 dollars.

Hair rebonding is hair straightening using the chemical treatment. It is a procedure done at the salons by professional rebonders. Source: beauty-cosmetic-guide.com/ hair-style-salon.org.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.