Type hinting return value with ^ or :tag meta?

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 开发者_StackOverflowsince it's shorter.

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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.

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Its 'a' that is canonical. Its the only one I have seen so far in Clojure code and in the documentation on the Clojure site. See here for more information on type hints.

Hope this helps.