add initialSourceIndexPath and finalDestinationIndexPath

[RickeyBoy]

When I intent to send a urlRequest that inform back-end the changes of model, I found that I can only do this in tableview(_:reorderRowAt:to).
However this means that during the Drag&Drop I have to send lots of urlRequest which is not necessary.
So I added two properties to help.
Usage:

func tableViewDidFinishReordering(_ tableView: UITableView) {
guard let rowS = tableView.reorder.initialSourceIndexPath?.row,
let rowD = tableView.reorder.finalDestinationIndexPath?.row else { return }
print("move (rowS) to (rowD)")
}

(This is my first pull request. Hope you don't mind if I make some mistakes. )

[adamshin]

Hey, thanks for contributing. This could definitely be useful.

I think initialSourceIndexPath and finalDestinationIndexPath might make more sense as parameters to the tableViewDidFinishReordering delegate method. That way there's no mutable state & no need to unwrap optionals. What do you think?

[RickeyBoy]

Yeah, I think you're right. And I changed initialSourceIndexPath and finalDestinationIndexPath to private.

Usage now becomes:

func tableViewDidFinishReordering(_ tableView: UITableView, initSource: IndexPath, finalDestination: IndexPath) {
print("(initSource) to (finalDestination)")
}

[adamshin]

You should be able to remove the initialSourceIndexPath and finalDestinationIndexPath properties altogether - both those values are available in the ReorderState.reordering case. We're unpacking the destination indexpath at the beginning of endReorder(), and we can access the source indexpath the same way. Currently that value's just being ignored.

[RickeyBoy]

I've removed those two properties in the way you said. Hope it works well now :)

[adamshin]

Looks good thanks!

One last thought: can you change the parameter names in that delegate method to

tableViewDidFinishReordering(_ tableView: UITableView, from initialSourceIndexPath: IndexPath, to finalDestinationIndexPath: IndexPath)?

A little more verbose, but consistent with the other methods.

[RickeyBoy]

All done! Really appreciate your patience and efforts- definitely made my first contributing experience an amazing one! Looking forward to cooperation in the future :)