As someone who is becoming more comfortable working in Objective-C I would like to be able to incorporate more design patterns and OOP features in my projects but struggle to implement them as required by GoF because you cannot create an abstract class. I want to 1) avoid lots of subclassing, 2) minimize use of respondsToSelector, conformsToProtocol, etc, 3) avoid techniques like swizzling as much as possible, 4) maximize encapsulation, and 5) avoid long conditionals or lots of typedef enum.
For example, in a recent project I wanted to separate RestKit (a library for accessing RESTful services) from my UIViewController subclasses. I did so by incorporating an Adapter between the two with a base class of ModelController, which could access models. I also created the ModelControllerDelegate protocol for my VC's to wire up. But I experienced great difficulty in creating a ModelControllerDecorator without the use of an abstract base class. I wanted to be able to decorate my ModelController with different aspects, like PaginationDecorator, CompressionDecorator, QueryableDecorator, and so forth.
I've heard that using Objective-C++ is one way to incorporate more OOP features, but how about using standard Objective-C language features? How have you been able to incorporate GoF design patterns that use C++ style features (like virtual classes) in your projects?
