Add removeObserver:forKeyPath:context: to implementation

[gcasa]

Addresses issue #322.

[rfm]

The interface looks fine.

I think we have two options for the implementation:

1. raise an exception to say that the method is not yet implemented.
2. implement the method to do what it's supposed to.

Implementing it as a synonym for -removeObjecter:forKeyPath: is IMO wrong since that would mean the app silently misbehaves.

[gcasa]

The interface looks fine.

I think we have two options for the implementation:

1. raise an exception to say that the method is not yet implemented.
2. implement the method to do what it's supposed to.

Implementing it as a synonym for -removeObjecter:forKeyPath: is IMO wrong since that would mean the app silently misbehaves.

I am not sure what the proper implementation is. I don't know what should be done with the "context" parameter.

[rfm]

I'm not familaiar with it either, but it looks from the documentation as if -removeObjecter:forKeyPath: should remove all observers, but -removeObjecter:forKeyPath:context: should only remove the observer which was added using the specified context (an opaque pointer).

[gcasa]

Since the context pointer is opaque I believe this is something that is left to the user to implement. I am going to do a bit more research on this. For now, I have made it so that the method throws an exception.

[triplef]

The context pointer is in fact not usable in GNUstep‘s current KVO implementation. I’ve opened #324 with some more details.

If you want to add this method you probably also want to add removeObserver:fromObjectsAtIndexes:forKeyPath:context:.

[rfm]

That looks plausible to me. If only we had testcases :-(

[gcasa]

That looks plausible to me. If only we had testcases :-(

I will add some as a separate PR. I will develop them on macOS.