C++ Software Design

Chapter 7. The Bridge, Prototype, and External Polymorphism Design Patterns

In this chapter, we will focus on two classic GoF design patterns: the Bridge design pattern and the Prototype design pattern. Additionally, we will study the External Polymorphism design pattern. At first glance, this selection may appear as an illustrious, almost random choice of design patterns. However, I picked these patterns for two reasons: first, in my experience, these three are among the most useful in the catalog of design patterns. For that reason, you should have a pretty good idea about their intent, advantages, and disadvantages. Second and equally important: they will all play a vital role in Chapter 8.

In “Guideline 28: Build Bridges to Remove Physical Dependencies”, I will acquaint you with the Bridge design pattern and its simplest form, the Pimpl idiom. Most importantly, I will demonstrate how you can use Bridges to reduce physical coupling by decoupling an interface from implementation details.

In “Guideline 29: Be Aware of Bridge Performance Gains and Losses”, we will take an explicit look at the performance impact of Bridges. We will run benchmarks for an implementation without Bridge, a Bridge-based implementation, and a “partial” Bridge.

In “Guideline 30: Apply Prototype for Abstract Copy Operations”, I will introduce you to the art of cloning. That is to say, that we will talk about copy operations and, in particular, abstract copy operations. The pattern of choice for this intent ...