Just like we have an ArrayMap for small maps, I propose to have an ArrayVector for small vectors.

Use cases:

• pair of values, e.g. coordinates, triples and other tuple values
• returning multiple values from a function and subsequent destructuring in a caller fn

ArrayVector has 100x faster vector creation compared to PersistentVector.
With an ^ArrayVector hint, it offers more than 10x faster destructuring. Without it, it is still about 40% faster.

Example of such destructuring:

(defn foo [a b] 
  [(+ a b) (- a b) (* a b)])

(defn bar []
  (let [[plus minus times] ^ArrayVector (foo 1 2)]
    (str "bla bla" plus "blaah" minus)))

I've attached a patch with complete implementation of such vector, supporting all basic functionalities as well as transients. This patch also replaces default vector implementation with ArrayVector, falling back to PersistentVector for large vectors.

ArrayVector implementation can also be found at array-vec branch at https://github.com/wagjo/clojurescript/tree/array-vec