From enumerator to map

Question

I have an mail object that returns its headers as an Enumerator of Header objects, which have two methods, getName and getValue. I need to convert that to a nice Clojure map so I wrote this short function:

(defn extract-headers [message]
 (reduce (fn [hs h] (conj hs {(.getName h) (.getValue h)}))
 {}
 (enumeration-seq (.getAllHeaders message))))

Anything to change or improve here?

Answer 1

You can use into, for example:

(defn extract-headers [message]
 (let [headers (enumeration-seq (.getAllHeaders message))]
 (into {} (map #(vector (.getName %1) (.getValue %1)) headers))))

first, with map you build sequence of 2-element vectors, that later is converted into map

Answer 2

Reading the other answer, a simple small improvement would be:

(defn extract-headers [message]
 (reduce #(conj %1 {(.getName %2) (.getValue %2)})
 {}
 (enumeration-seq (.getAllHeaders message))))

Only to make it a little shorter.

• Alex Ott: use of explicit fn could make life easier + it allows to put type hint before argument

Answer 3

I rather like the into approach, I think it's more idiomatic to use a dedicated function than reduce, which is quite general. However, I think using threading is easier to read long term.

(defn extract-headers [^Mail message]
 (letfn [(project [^Header h] (list (.getName h) (.getValue h)))]
 (->>
 message
 .getAllHeaders
 enumeration-seq
 (map project)
 (into {}))))

As you can see, I've also incorporated Alex's suggestion to use an explict fn, which avoids reflection.