WatchOS support for Diffing

[jlaws]

It would be great to have the Diffing subspec for WatchOS, is there a reason why it's restricted to iOS/TVOS/MacOS currently?

[rnystrom]

Great question! The diffing part should easily be usable in watchOS. Is our CocoaPods setup now restricting that? If so, I’d instantly accept a PR to change that.

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[Sherlouk]

IIRC the issue was when I looked at this previously that the diffing code has pretty strong references to an IndexSet which is currently not in watchOS

This may be wrong though so definitely worth a check!

[ajkolean]

Just checked. Indeed, it looks like the issue lies with the property `section' of NSIndexPath being defined in UITableView.h of UIKit.

[jlaws]

Sounds like NSIndexPath/IndexPath need to be abstracted behind a protocol so that WatchOS can have its own implementation. Would a change like that work for a PR?

[rnystrom]

NSIndexPath is available in watchOS, just not the UIKit extensions (section, row, item). We should be able to easily use the basic version of NSIndexPath (using actual index paths to represent section/item).

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[futuretap]

I wrote this, maybe it's helpful: https://github.com/futuretap/IGListKit/commit/f785f5bde572a65756a8c2ebe138e721d02b6ba5

[TimOliver]

@futuretap Oooh! Fantastic! Absolutely! Could you please add that as a PR? 🎉🙏

[futuretap]

I'm hesitant since I no longer use IGListKit, so the code isn't tested against HEAD. But feel free to grab it.