🚀 go-pugleaf

    From: barmar@think.com (Barry Margolin)
    Sender: commonloops-request@cis.ohio-state.edu
    References: <odvAqcy00iQQRD=Fo6@andrew.cmu.edu>state
    Subject: Re: no-applicable-method

    . . .

    But it might be better to use an OO technique.  Define subclasses of
    GENERIC-FUNCTION that delegate on specific arguments, and use this as the
    metaclass of the generic functions that you want to be delegated.
    Something like:

    (defclass delegatable-normal-gf (generic-function))

    (defmethod no-applicable-method ((gf delegatable-normal-gf) &rest args)
      (let ((prototype (prototype (first args))))
	(if prototype
	    (apply gf prototype (cdr args))
	    (call-next-method))))

    (defclass delegatable-setf-gf (generic-function))

    (defmethod no-applicable-method ((gf delegatable-setf-gf) new-value object)
      (let ((prototype (prototype object)))
	(if prototype
	    (apply gf prototype new-value)
	    (call-next-method))))

    However, this won't work if you're trying to do this to generic functions
    that you don't define yourself, since you can't override their metaclasses.


this will work fine. assuming that you can get at the generic functions,
just change the class of the generic function object, like so:

(defclass delegatable-normal-gf (standard-generic-function)
    ()
  (:metaclass clos:funcallable-standard-class))

(defgeneric frob (thing))

(let ((gf (symbol-function 'frob)))
  (change-class gf (find-class 'delegatable-normal-gf)))

(symbol-function 'frob) ==> #<DELEGATABLE-NORMAL-GF FROB 22011004736>