design patterns

With all the posts about Objective-C and design patterns lately that David's been posting, it's only fair that we bring back some of it to Python with some simple patterns. So, let's steal the strategy pattern one today!

When working with the Observer Pattern and the Singleton Pattern it is easy to see how they relate to the Java or C++ versions of the same concept. Everything basically plugs into the same places you would expect, coming from another Object Oriented language. The implementation isn't all that different.

We are going to see something a little more interesting when working with the Strategy Pattern in Objective-C. The Strategy Pattern is one of the most basic patterns and is even covered in the introduction to Head First Design Patterns. While the concept is identical in Objective-C as it is in Java and C++, the implementation is much closer to languages with first-class functions such as Python.

To do this, we will take advantage of one of the more powerful features of Objective-C: Forwarding.

One of the most common patterns, after the Singleton, in Java is the Observer Pattern. Also referred to as a Broadcaster/Listener or a Publish/Subscribe pattern. The basic principle is that there are two components: An Observer (or Listener) and a Subject (or Broadcaster).

One of the challenges in switching to a new language is figuring out how design patterns adapt. Sometimes the language has built-in facilities for the pattern, or features that work-around what the pattern was designed to do in the first place.