Re-compiling on need basis

• Objective C provides a way to limit the effects of dependency-caused re-compilation.

• Dependency issue exists because the Objective-C compiler needs certain piece of information to be able to do its work.

• Sometimes compiler needs to know everything about the class, such as instance variable, layout and which classes it ultimately inherits from.

• Sometimes the compiler only needs to know is name of class rather than entire definition

• Object C introduces @class keyword as a way to tell compiler “This thing is a class and I am only going to refer to it via pointer”

• This calms the compiler down: it doesn't need to know more about the class, just that it's something referred to by pointer.