Should ifLet(then:else:) call else block for initial nil?

[mluisbrown]

The ifLet(then:else:) Store function for use with UIKit will call the else closure when the optional state is initially nil, which seems counterintuitive. The documentation also says:

else: A function that is called whenever the store's optional state goes from non-nil to nil

If it starts as nil it's not going from non-nil to nil.

I would imagine that in the vast majority of cases these states will always start as nil. In our project we use this a lot and we have no optional states that start as non-nil.

Having the else closure called initially could lead to some unexpected issues if you are not careful. For example, if you are using this for UIKit navigation, you might be calling viewController.popViewContoller(animated: true) in the else block. If you are not checking that the VC you presented in the then block exists, this could cause some unexpected behaviour!

This could easily be fixed by adding a drop(while: { $0 == nil}) to the else publisher, thus skipping any initial nil value.

If you agree, I'll create a quick PR for this change.

PS: I created this here instead of an Issue as not sure if it's strictly a bug.

[mluisbrown]

I had a deeper look at this, and it turns out that suppressing the else block for an initial nil is probably not such a good idea after all. For one, it would remove the ability to do this kind of thing. Here the initial nil is used to show a loading spinner in a navigate then load scenario.