Suggested addition: index-of

[orestis]

The humble indexOf -> you have a known small vector or sequence, you are doing ops on it and you want to find a particular element's index. (Because you have to e.g. replace it later, or put something before or after it).

Naive implementation:

(defn index-of
  "Return the first index of x inside a seq of xs, or nil"
  [xs x]
  (->> xs
       (medley/indexed)
       (medley/find-first (fn [[_idx item]]
                            (= item x)))
       (first)))

[borkdude]

If you already have a vector, you can just use .indexOf in the implementation, for performance.

[orestis]

True, if you know what you have. But .indexOf will also use identical? instead of =, right? This might be a reason to add this more generic index-of -- if someone needs absolute performance they would stick with vectors and use .indexOf. In any case, this is more a convenience (for me) when manipulating very small vectors (e.g. up to 10 items)

[borkdude]

@orestis I don't think it does:

https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/APersistentVector.java#L186-L191

I mean, if you're going to implement this as part of this library, it's fairly cheap to check vector? first and then call this, and for other cases fall back on the seq behavior.