[cells-devel] Controlling order of initialization?

[Kenny Tilton]

Mikko Ahonen wrote:
> Hmm, here follows a question about controlling the order of initialization.
> 
> For example, let's assume we want to create a radio button group with 
> individual radio buttons as kids. The invidual radio buttons are 
> generated automatically based on the arguments passed to make-instance 
> of the radio button groups.
> 
> Thus, the kids are generated in the initialize-instance of the radio 
> button group. They must get created before call to apply-next-method. 
> The problem is that when I generate the child here, it wants to read 
> stuff from the parent, which is not yet completely initialized. For 
> example, it wants to read which kid is selected (parent's selected cell) 
> before any kids even exist!
> 
> I guess this is more generic problem of controlling the order of 
> initialization of children, and perhaps delaying it until after the 
> initialization of the parent. How do people usually go about doing this?
> 
> I can think of some work-arounds. For example set parent's selected cell 
> to nil, and then ignore this value in kids. Or define some new state 
> cell in the parent, which children watch for.
> 
> But isn't this a quite generic need in cells programs?

Yes, and in the first few days I suspected this (instances coming and 
going while being interdependent) was where the apparent wonderfulness 
of Cells would fall apart. :) When it didn't I had another reason to 
suspect we were onto something Deeply Correct.

But you do have to stay with the Cells paradigm, and it sounds like you 
are just a bit outside that if you are making kids in initialize-instance.

Instead, make them in a rule on the kids slot of family. But "kids" was 
generalized recently so you can also make them in a rule on any slot for 
which you also specify ":owning t", a Cells extension.

There should be a pile of examples in the test code.


kt