[cells-devel] Cells: Controlling the way kids are added to a parent ...

[Frank Goenninger]

Hi -

I want to control if a kid is added to a parent based on the execution  
of a check function. The check function is supposed to throw an  
condition when the check fails.

Current use case:

Control which classes of kids are added to a parent. I do have a model  
of class BOM (bill of material) that only can accept classes Assembly  
and Part as kids.

I found two places at which I could insert a call to the check function:

function fm-kid-add (higher level interface)
function fm-kid-insert (lower level interface)

Question now is: Why would one be better than the other?

Idea here is based on adding a new slot to class family:

(defmodel family (model)
   ((.kid-slots :cell nil
      :initform nil
      :accessor kid-slots
      :initarg :kid-slots)
    (.kids :initform (c-in nil) ;; most useful
      :owning t
      :accessor kids
      :initarg :kids)
    (registry? :cell nil
      :initform nil
      :initarg :registry?
      :accessor registry?)
    (registry :cell nil
      :initform nil
      :accessor registry)
    ;; added: frgo, 2008-10-30    -----
    (kid-add-control-hook :cell nil
                          :initform nil
                          :initarg: kid-add-control-hook)))

and then do run the check functions that have been added to the  
control hook (= list of functions to be funcalled).

Right approach? Any comments? (It works but I'd like to know if am on  
the right track).

Thanks for feedback.

Cheers
     Frank




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