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Decorator Design Pattern


For this week's blog on Software Design, I decided to watch a short tutorial on one of the design patterns I didn't pick for a previous assignment. I picked Proxy Design pattern to cover before, and now I'm going back to learn about Decorator Design Pattern. It is only a thirteen minute video, so I won't be going as deep as I would had I picked it for the assignment. I am also going to talk about my reflections on it rather than create a tutorial, so I am not going to reteach it to the person reading this blog post.

The tutorial I chose was made by Derek Banas on YouTube. He used an example of a pizza parlor to illustrate the wrong way to code it by using inheritance. He shows the problem with this because you would have to create a very large number of subclasses for all your objects (in this case pizzas).

Composition, on the other hand, is a dynamic way of modifying objects. Instead of creating as many subclasses, you add functionality at run time. It has the benefits of inheritance, but is better to implement in many cases because it is more flexible. Instead of rewriting old code, you extend with new code.

This seems like a more intuitive way of doing things. In the example in the video, he uses the example of creating different kinds of pizza. If you were to design a menu for the same pizza place and there was twenty ingredients and different prices for each, it would make more sense to list the cost of the sizes “Small $5, Medium $7, etc.” and the prices of the toppings in a similar way, with Pepperoni and Sausage being 50¢ and 65¢ respectively. The customer would then choose the size and toppings and add all those together to get the total price.

It seems like the decorator does exactly this. It would seem silly for a pizza shop to list every permutation of toppings and sizes. It would make sense if there were only a handful of pizzas to choose from, but it does not make sense to do this if there are too many ways to list. Same with inheritance instead of decorator design pattern. The same logic is true with inheritance. This seems like an incredibly useful and versatile tool to use. I think learning about this will be incredibly invaluable for the future.

http://www.newthinktank.com/2012/09/decorator-design-pattern-tutorial/

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