[MacRuby-devel] kvo vs referenced hash

[Benjamin Stiglitz]

>  Coming from a Ruby background, I try to understand and pick the  
> best from Obj-C/Cococa and learn how to use brilliant ideas to  
> improve my coding.
>
> Tonight I was working on a simple demo app to learn how things are  
> done in the Obj-C world and see how they would transpose to the  
> MacRuby world.
>
> Everything went well until the KVO question came along.
>
> Let's say I have a controller that we are going to call Brain.
> We also have a lot of simpler objects that don't do anything but  
> having a state and being displayed, we are going to call them Task  
> instances. The brain is called every X seconds to "think".
>
> My understanding is that an Obj-C developer would register all the  
> tasks instance with the brain using a KVO and the brain would send  
> notifications when it's being called to "think".  So, every time a  
> new task is being created, an observer is added on the brain with  
> the new task key. Each Task instance has an  
> observeValueForKeyPath:ofObject:change:context: method implemented  
> which checks that the notification is meant for itself and if it is,  
> to act accordingly.
>
> While the concept is simple and attractive. I wonder if it wouldn't  
> be simpler to forget about kvo's and simply keep the list of  
> registered tasks in the brain and the brain would call the tasks  
> directly and tell them to change.
>
> It sounds to me that in the MacRuby world, it would be more  
> efficient. If we have 250 tasks for instance, when a notification is  
> being sent, every single task in the 250 tasks created, will receive  
> the notification and will check what to do with it. If we had a  
> simple hash/dictionary in the brain, we could directly find the task  
> to handle and call it directly without having to go through the 250.
>
> Am I missing something or in this specific case and because we use  
> Ruby, KVO aren't the way to go?

KVO isn’t really the right hammer for your nail, but I’m not sure I  
understand your scenario properly.

You have a Brain which every «interval» picks a task to work on and  
does some work.

KVO is about observing changes in a key’s value and doing something  
with it. It’s an inter-object dependency mechanism. A common way to  
use it is to update some UI when the value of a model object’s key  
changes. An example:

You have a table view which shows the current state of all your tasks.  
Each task is just a countdown from 10 to 0, and you want the table to  
display what stage in the countdown each object is at. Your controller  
observes all the tasks, and when a task changes it tells the  
appropriate row in the table to refresh.

In your case, the Brain has nothing the tasks are interested in  
observing. “I’m doing some work” doesn’t make sense from an OO point  
of view since the Brain should be doing the work and not the Task.

Hope that helps,

-Ben