I am implementing a custom data structure, that, for all intents and purposes, is a sorted map. I wanted to program it so that I can use all of clojure's abstractions when it comes to maps, such as assoc, count, etc. In order to do that, I need to extend clojure's clojure.lang.IPersistentMap protocol to my new sorted map type.
My question is this: What does assocEx do, or what is its purpose? Calling it on a normal clojure map shows that it differs from assoc in that it throws an exception if you try to insert a key/value pair where the key already exists in the map:
user> (.assocEx (cast clojure.lang.IPersistentMap {:a :b}) :a 1)
RuntimeException Key already present clojure.lang.Util.runtimeException (Util.java:219)
This is different from assoc, which simply replaces the old value in the map with the new one:
user> (.assoc (cast clojure.lang.IPersistentMap {:a :b}) :a 1)
{:a 1}
But I can't seem to find a "clojure" function (one where the interop form/cast is not used above) that displays this functionality. Where do we see the effects of this function using the normal clojure abstraction functions like assoc?
Nothing ever uses assocEx anymore. It is a remnant of an earlier time. If you are writing your own map type, you can implement (assocEx [m k v] (throw (Exception.))).