As I understand it, Protocols are intended to basically do what Interfaces do in Java: define a contract whereby clients can reasonably expect certain operations to be defined, irregardless of what they actually do.
shameless opinion: this is a powerful and sexy sexy sexy language feature that should be used by everyone. Program to an Interface, not an Implementation <http://www.artima.com/lejava/articles/designprinciples.html> . You are basically replicating the Interface-->Abstract Class--> Concrete Implementation pattern in Clojure. Some might immediately regard this as an OOP-type "code-smell", in the Functional world. But I would argue that the very introduction of Protocols in Clojure suggests that there's value in this pattern. There are times when your clients want to be assured that certain functionality is available. There are also times when a framework designer wants to be able to say "make whatever piece you want, but in order to maintain semantic cohesion with the rest of the pieces you must provide this functionality." There's a reason this Language Pattern comes up again and again. What you're doing, in this sense, is enabling easy understanding of your system by adhering to Domain Driven Design<http://domaindrivendesign.org/resources/what_is_ddd>, keeping things Simple (concepts have first class representations) and Easy to understand (the concepts themselves are small). Your clients only need to know about your Protocols and your Entity. They don't ask an entity about its state and then do stuff. They tell an entity what to do based upon the operations it declares it can do. You define dummy operations, then each individual entity says "I'm not dumb! I actually do stuff!" only about the things it cares about/can actually do. Seems reasonable. You can contrast your usage with others such as Luke VanderHart's Domina: https://github.com/levand/domina/blob/master/src/cljs/domina.cljs, which seems like a fantastic use of Protocols to abstract away details of handling nodes. Though, personally, I find putting all of that in one file to be one giant code smell. There's a Parser hidden in there. The concept of a Node is just screaming to get out into its own space. A Debug mode is just praying to get away from all this other noise. A StyledNode is wondering why no one's ever considered that it's a really pretty Decorator that makes Node easier to understand in isolation but much nicer in application. I like your approach better. I would like it even more if you're being extra considerate and keeping things to Miller's Magic Number<http://en.wikipedia.org/wiki/The_Magical_Number_Seven,_Plus_or_Minus_Two>for information processing (and code comprehensibility) by having separate files with a nice package structure, such as: domain/Entity.clj protocols/Movement.clj domain/AbstractEntity.clj domain/Farmer.clj My only feedback is to think about the size of your Movement protocol. Are asset and data really cohesive to the idea of movement? I'm unclear as to what you might mean by such names, so it's hard to tell. Is inspecting and materializing really a part of Movement? Are asking questions about destination really key to the idea of Movement? Is location really a function of Movement, or a first class piece achieved via movement? Ideally Protocols should be small. Perhaps you have another Protocol that extends Movement? Perhaps you have a Watcher Protocol that asks questions about destination? An Organism, that extends both Movement and Watcher and tries to survive? Keeping such pieces small and composable, highly cohesive and loosely coupled, increases your flexibility in the future. My Not So Humble Opinion: Not only is it correct, it's also beautiful. Keep using it this way. On Tue, Apr 10, 2012 at 7:44 AM, tmountain <tinymount...@gmail.com> wrote: > I'm working on a behavior simulation demo in Clojure, and I've opted to > use protocols as a mechanism for composing entity capabilities. This > snippit of code demonstrates what I'm doing: > > https://gist.github.com/2351790 > > Everything is working so far, but I'm wondering if this is an idiomatic > usage of protocols and records. I ask this specifically because I'm getting > a code smell type feeling in duplicating all the keys from Movement in my > base-behavior map. > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
