7.3. Core Foundation

Foundation provides a set of Objective-C classes like NSString, but many of these classes actually use code in a lower-level C framework called Core Foundation. You usually don’t have to think about any of this, because Cocoa handles the details for you, but there is code out in the world that refers to this framework directly.

Even if you don’t use it every day, it helps to at least understand the basics of Core Foundation, because some other frameworks are based on the same ideas. First, here’s a quick test to show you something about the NSString class: