Miscellaneous JVM Considerations

Because of the way protocols are implemented on the JVM, there are a couple of considerations to keep in mind, one about performance and one about semantics, and they would each push you in different directions.

Performance Gotcha

The performance of Clojure protocols is a bit nuanced. A Clojure protocol generates a Java interface, a protocol, and some protocol functions. The protocol functions will dispatch through the Java interface if the type of the first argument implements the interface; otherwise, it will dispatch through the protocol's dispatch table.

There are two ways to implement a protocol in Clojure:

1 (defrecord S3Storage

2     [access-key secret-key]

3   proto/IStorage

4   ...)

Or:

1 (defrecord S3Storage

2     [access-key secret-key])

3

4 (extend-protocol IStorage

5   S3Storage

6 ...