goops: initialize :after

[David Pirotte]

Hello,

I can not find similar methods in goops then we had in CLOS:

        defmethod initialize-instance :after ((blabla <...> ) &rest args)

and

        defmethod (setf ...) :after ...

here is my problem: I wish to define a class a slot of which will
store a date as an integer and a date as a valid string date

(define-class <chantier> ()
  ...
  (dte-dmis #:init-value #f #:accessor dte-dmis #:init-keyword #:dte-dmis)
  (dte-dmis-str #:init-value "" #:accessor dte-dmis-str #:init-keyword 
#:dte-dmis-str)
  ...
  )

but I would like that at intialization time, only passing

        #:dte-dmis-str <value>

it calls something that would 'initialize' the other slot, dte-dmis
BUT only if

        #:dte-dmis is not given


in the same spirit, I'd like to be able to define (redefine)
the set!, which would take optional arg so that if I already know the
date-number of a date, I don't need to compute but just affect the other
slot:

        (define-method (set! dte-dmis-str) :after (dte-dmis-str (obj 
<chantier>) . dte-nb)
           ...
           )
           
can anyone knowing goops better then I has an idea ?
thanks,
david