Clojure Programming

Chapter 18. Choosing Clojure Type Definition Forms Wisely

Clojure provides a number of different forms useful for defining types:

• deftype, defrecord, and reify, Clojure’s primary datatype abstractions, explored in Defining Your Own Types

• Maps of all sorts, particularly useful for the most flexible de facto types, discussed in Chapter 3

• proxy and gen-class, which focus on providing comprehensive Java and JVM interoperability, covered in Defining Classes and Implementing Interfaces

Each of these forms represents a different set of tradeoffs. Especially when you are new to Clojure, it may be difficult to determine when one type-definition form should be used over another. When should you use deftype instead of defrecord, gen-class instead of deftype, or proxy instead of reify?

We have attempted to explore all of the nuances of these forms in the sections referenced above. However, it is sometimes helpful to have a visual reference for such things, even if it is summary in nature. With that in mind, we hope you will find the flowchart in Figure 18-1 useful. Starting with the premise that you would like to define a type in Clojure, it will guide you through the most significant points of distinction between the type definition forms in the language so that you can settle on the one that is right for your particular situation:^[428]

Figure 18-1. Choosing Clojure type definition forms wisely

“The ...