Association Callbacks: after_create/before_create

Hi,

I was thinking of creating a patch to include two new association
callbacks, after_create and before_create. These would work exactly
the same way that after_add and before_add would work, but would be
called when an item is added to the collection when calling create.

Do you think there is any value in this?

What's the use case you have in mind? Given that we have after_create
and friends on the model themselves, I can't really think of anything
off hand. Perhaps an example would people figure out if they think
there's some value?