Question

The two seem to be doing the same thing in Clojure. Which syntax is canonical?

(defn a ^int [] 4)

(defn b ^{:tag int} [] 4)

I hope it’s a since it’s shorter.

Answer 1

I only use b when I need to include metadata other than just the tag. For example, when implementing a transient collection, I needed

(deftype Whatever [^{:tag ITransientVector
                     :unsynchronized-mutable true} foo])

Note that it would be equivalent and perfectly acceptable to write

(deftype Whatever [^:unsynchronized-mutable ^ITransientVector foo])

but I personally prefer the explicit map.