I was playing with built-in specs and discovered there are A LOT of places to embed var metadata in defn:

(defn ^{:b 1} foo
  {:c 1}
  ([])
  {:a 1})

I wonder how's that, and why :arity-n defn variation allows attr map at the end...

I found that when I spec’ed it and asked Rich about it. The thought at the time was that metadata might get big (this predated some of the ^ syntax) and it would obscure the main part of the function so you could put it at the end

It’s rarely used but I did find some places using when testing a spec without it

Very interesting, thanks for this explanation!