Why the autorelease pool is necessary in main.m?

Cocoa Development: When does an autorelease pool get deallocated?

• It's a question with many answers on the internet, but it's kind of hard to get around it. Can someone explain it nicely?

• Answer:

  NSAutoeleasePool objects are under the same Memory-Management rules like any other object. The catch here is that a pool may not be an autorelease object and you may not retain it, either. On iOS (that doesn't have GC), calling 'drain' and 'release' on your autorelease pool are effectively the same thing - that means that your pool gets deallocated the moment you call 'drain' on it. Calling release and drain are exactly the same thing, but if you call release in an NSAutoreleasePool you created, it may throw off the developer who has to maintain your code. Things are a bit different when you are working in GC environments (Mac OS X, as a relevant example). In a GC environment, there's no use to have autorelease pools. However, if you are writing a program for GC environments but plan on giving it support for non-GC environments, you cannot call 'release' on an autorelease pool, but you may freely call 'drain' on it, and the moment you do that, you are actually triggering Garbage Collection, rather than draining the 'pool' itself. Hope this is clear enough. If something is not clear, feel free to ask.