Chapter 9. The Decorator Design Pattern

This chapter is dedicated to another classic design pattern: the Decorator design pattern. Over the years, Decorator has proven to be one of the most useful design patterns when it comes to combining and reusing different implementations. So it doesn’t come as a surprise that it is commonly used, even for one of the most impressive reworks of a C++ Standard Library feature. My primary objective in this chapter will be to give you a very good idea why, and when, Decorator is a great choice for designing software. Additionally, I will show you the modern, more value-based forms of Decorator.

In “Guideline 35: Use Decorators to Add Customization Hierarchically”, we will dive into the design aspects of the Decorator design pattern. You will see when it is the right design choice and which benefits you’re gaining by using it. Additionally, you will learn about differences compared to other design patterns and its potential shortcomings.

In “Guideline 36: Understand the Trade-off Between Runtime and Compile Time Abstraction”, we will take a look at two more implementations of the Decorator design pattern. Although both implementations will be firmly rooted in the realm of value semantics, the first one will be based on static polymorphism, while the second one will be based on dynamic polymorphism. Even though both have the same intent and thus implement Decorator, the contrast between these two will give you an impression of the vastness of the ...

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