EIEIO: how to validate a new instance?

[Raffaele Ricciardi]

Hello everyone,

I need to create a new EIEIO object, but not all values are acceptable as
initargs.  My understanding is that I should use initialize-instance for 
checks,
but I can't find the proper incantation to make it work (I even managed 
to make
Emacs crash).

Here is a sample code:

(require 'eieio)

(defclass my-class ()
  ((x :initarg :x
           :type string )))

So far, so good.  I can instantiate my class:

(setq ^c (my-class "my-class" :x "x"))

Here is one of my attempts at initialize-instance:

(defun initialize-instance ((^c my-class) ^args) nil)

It doesn't work: now I can't instantiate my class anymore:

(setq ^c (my-class "my-class" :x "x"))

Fails with:

> Debugger entered--Lisp error: (invalid-function (lambda ((^y 
my-class) ^args)
nil))
> initialize-instance([object my-class "my-class" unbound] (:x "x")) Any
help?  Thank you.