Question

Here’s part of an overloaded protocol definition:

(defprotocol ClientProtocol
  (create-edge
    [this outV label inV] 
    [this outV label inV data])

And here’s part of its implementation:

(ns bulbs.neo4jserver.client
  (:use [bulbs.base.client :only [ClientProtocol]]))

(deftype Neo4jClient [ns config]
  ClientProtocol

  (create-edge
    [this outV label inV data]
    (let [inV-uri (utils/normalize-uri (build-path neo4j-uri vertex-path inV))
          path (build-path vertex-path, outV, "relationships")
          params {:to inV-uri, :type label, :data (first data)}]
      (post config path params)))

  (create-edge
    [this outV label inV]
    ;; it doesn't like this call...
    (create-edge this outV label inV nil)) 

It’s spewing this error when the second method tries to call the first:

java.lang.RuntimeException: Unable to resolve symbol: create-edge in this context

I had both definitions working earlier in SLIME when I compiled it with the first function and then went back and added the second.

But when I moved the protocol definition into a separate file and tried to re-compile the whole thing, it throws an error when the second method tries to call the first, presumably because the first method hasn’t been defined yet.

The Clojure reify docs have this comment:

If a method is overloaded in a protocol/interface, multiple
independent method definitions must be supplied.

http://clojure.github.com/clojure/clojure.core-api.html#clojure.core/reify

I suppose these are not independent definitions.

What’s the right way to approach this?

Answer 1

Your namespace declaration is wrong.

(ns bulbs.neo4jserver.client
  (:use [bulbs.base.client :only [ClientProtocol]]))

Protocol functions are normal Clojure functions and have to treated as such. So you have to include them in your :only clause.

(ns bulbs.neo4jserver.client
  (:use [bulbs.base.client :only [create-edge ClientProtocol]]))