;;; -*- lexical-binding: t -*-
(require 'eieio)
(require 'eieio-base)

(defclass eieio-fail (eieio-persistent eieio-named)
  ((version :initarg :version :initform nil)
   (version-constant :allocation :class)
   (entries :initarg :entries :initform (make-hash-table))))

(let* ((ef (make-instance 'eieio-fail :file "tmp"))
       (entries (slot-value ef 'entries))
       (ef2 (make-instance 'eieio-fail :file "tmp2"))
       (entries2 (slot-value ef2 'entries)))
  (puthash 'foo 42 entries2)
  (oset ef2 :entries entries2)
  (puthash 'ef2 ef2 entries)
  (oset ef2 :entries entries2)
  (oset ef :entries entries)  
  (eieio-persistent-save ef (concat "tmp-" emacs-version)))

(let* ((ef (eieio-persistent-read (concat "tmp-" emacs-version) 'eieio-fail t))
       (entries (slot-value ef 'entries))
       (entries2 (slot-value (gethash 'ef2 entries) 'entries)))
  ;; (pp ef)
  (pp (gethash 'foo entries2)))