[Tutor] list of references to object properties

[Alan Gauld]

On 18/01/13 11:11, Jose Amoreira wrote:

> Suppose I have a list l_obj of similar objects. Is there any way I can
> generate a list l_prp of references to a given property of those objects
> in such a way that, if change the value of one element in l_prp, the
> corresponding object in l_obj gets its property updated, and vice-versa?

Not easily, and for very good reason, it breaks one of the fundamental 
principles of OOP. Objects should manage their own data and clients 
should manage the objects.

So getting a list of the prp values is fine. Trying to modify those 
values without going through the object is asking for trouble and 
creating a nightmare for debugging. So unless you have a very specific 
reason to do so just modify the objects prp through the object.

> As expected, changes in l_prp do not change the properties of the
> elements in l_obj, neither do changes in l_obj's element's properties
> change the values in l_prp.

As you say, it's as expected and very worrying if it did otherwise!

> Is there a simple way to implement such connections?

It's difficult by intent. It's to save you from yourself.

Is there a good reason to want to do such a thing?


-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/