Hi,

While exploring eieio I found that laconic comment

--- snip ---
;; In retrospect, this is a silly function.
(defun eieio-instance-tracker-find (key slot list-symbol)
  "Find KEY as an element of SLOT in the objects in LIST-SYMBOL.
Returns the first match."
  (object-assoc key slot (symbol-value list-symbol)))
--- snip ---

So I thought I could make my own query for a tracking list of eieio
objects. It is a macro that use pcase to destructuring-bind the argument
list into a query that may returns matching objects or slots
or whatever.