Argument to ivy-read action when collection is an alist

Question

The documentation of ivy-read states that if the collection supplied is an alist, the selected candidate is passed as a cons cell to the function supplied in the :action argument.

So why does the code snippet below return "C1" or "C2", depending on the selection, and not (1 2 3) or (3 4 5), respectively?

(ivy-read "Choose: "
          (list (cons "C1" (list 1 2 3)) (cons "C2" (list 3 4 5)))
          :action (lambda (x) (cdr x)))

I can work around this by doing something like the following, but I don't understand why I have to.

(let (tmp)
  (ivy-read "Choose: "
            (list (cons "C1" (list 1 2 3)) (cons "C2" (list 3 4 5)))
            :action (lambda (x) (setq tmp (cdr x))))
  tmp)

Answer 1

So why does the code snippet below return "C1" or "C2", depending on the selection, and not (1 2 3) or (3 4 5), respectively?

Because the argument passed to :action is not, and is not documented as being, the same thing as the return value of ivy-read. The value returned by ivy-read is usually, but not always, the same as what completing-read would return. This is done to allow ivy-completing-read to be used as a completing-read-function. Ivy :actions, OTOH, are intended for Ivy-specific features like non-exiting completion, multi-actions, etc.