Question

I’m a Clojure novice and was looking for some concrete examples of when to use protocols and when to use multimethods. I know that protocols are generally geared towards creating a type hierarchy and typical OOP things, that they were added to the language after multimethods, and that protocols generally have better performance so my question is this:

Are protocols meant to replace multimethods? If not, could you give me an example where I would use multimethods instead of protocols?

Answer 1

Multimethods are more powerful and more expensive,

use protocols when they are sufficient but if you need to dispatch based on the phase of the moon as seen from mars then multimethods are your best choice.

Protocols exist to allow the simple stuff to stay simple and provide a way for clojure to generate very much the same bytecode that the equivalent java would. It seems that most people use protocols most of the time. I use multimethods when I need to dispatch on more than one argument, though I have to admit that this has only come up once, and full isa hierarchies are used even less often (by me). so in short use Multimethods when you need them

the best example In my expierence is right at the start, in core.clj