xcode 4 garbage collection removed?
macos, objective-c, xcode
Solution
Xcode 4 still has Garbage Collection, all you do is go into your project (the top option in the navigation bar with the big xcode project icon). Select your target which should just be the name of your app with the application icon next to it. When you select that, along the top there is a bar with different options, such as summary, info, build settings etc. Hit "Build Settings" and type "garbage" in the search field. Then set garbage collection to required.
One very important note about GC is that it is officially deprecated as of Mac OS 10.8, which means you should be transitioning your code to ARC if possible because GC might not be around for much longer.
Update: See other answers for enabling GC in current versions of Xcode. As I stated above, you should be transitioning to ARC if you haven't already.
Problem
I am learning Xcode and objective c, but the book I am reading is using the older version (3.2) of Xcode. One chapter, which is completely dedicated to memory and leaks, says I need to turn on garbage collection through Project Settings > Build. However, I can't find the garbage collection setting. Has it been removed or am I just missing it?