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I'm watching a course about Design Patterns and the example they used for decorator pattern is the Pizza and Toppings example ( you can find the example here as well). Please have a look at the link to understand my issue

What I don't like about this pattern as mentioned in the comments of the link I added is that a topping is not a pizza so why should it inherit the pizza class?

The solution I have in my mind is using an array of PizzaDecorators objects in a Pizza object and use that array to add or remove toppings from a pizza.

Isn't this solution much simpler than using the decorator pattern? Why should we consider using the decorator pattern in a situation like this?

Morez
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1 Answers1

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...a topping is not a pizza so why should it inherit the pizza class?

This comment was answered in the subsequent one: it's simply an issue of naming. Each topping should be named PizzaWithTopping.

...use an array to add or remove toppings from a pizza?

This solution makes a couple of assumptions.

  • Do you own the Pizza class? You might be making pizzas for a specific store, where the Pizza is determined by a franchise. One way the franchise controls quality is by not allowing individual stores to edit the base Pizza code.
  • Is a Pizza object mutable? Mutability leads to bugs that immutability can avoid. This is a bigger architectural decision than just editing an array.

Why should we consider using the decorator pattern in a situation like this?

The main advantage of the Decorator pattern over a "collection of enhancements" is that Decorator obeys the Open-Closed Principle. Decorator applies equally to any class, whether you own it or not, and whether the enhancements are foreseeable or not.

A collection requires that you either,

  • See the future and plan ahead by adding a collection (of enhancements with the right interface) to every base class, or...
  • Edit the existing base class in violation of the OCP.

In a well-known and relatively small domain like Pizza, this might not be a serious problem. Maybe the toppings never become more complex than adding one-at-a-time through a single API. But with the Decorator, you're covered either way.

jaco0646
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