Question

I’m at loss of how to create a Java enum in Clojure. I want to create a Java enum that uses a Java interface and then pass it into a Java method, all within Clojure. I want to do this to work with the neo4j graph library (I don’t want to use someone’s prebuilt interface, I want to write my own interop code).

I searched around the internet, and it looks like I can use the proxy method, but I can’t for the life of me get it to work. Here’s the equivalent Java code I need to write in Clojure:

private static enum RelTypes implements RelationshipType
{
    KNOWS
}

And here’s my stab at it (It’s not right 🙁 ):

(proxy [org.neo4j.graphdb.RelationshipType] [] (KNOWS))

I’m also wondering if there’s a good website that documents things like this that I’m missing. I know about the Clojure docs on the Clojure site, which is really useful, but for example of usage I can’t always find what I need. Perhaps I need a good reference book?

Answer 1

Why not just create the enum in Java? Sometimes falling back to Java is the simplest answer.

Here is a very old thread about using proxy to define enums from Rich Hickey and Stuart Sierra along with some alternatives using gen-class. I think the proxy path should work with something like this for you:

(proxy [Enum org.neo4j.graphdb.RelationshipType] [ "KNOWS" 1 ])

But that won’t generate anything you’d want an external Java user to use, in which case gen-class is likely the better solution.