What problems does diffable data source solve, and what does it not solve?

Answer

What it solves

Diffable data source reduces the fragility of manual batch updates. You stop reasoning about index path mutations first and start reasoning about state transitions and item identity.

What it does not solve

It does not invent stable identifiers for you.
It does not fix a poor view model or domain model.
It does not eliminate performance concerns when snapshots are huge or rebuilt too often.

Example explanation

swift

var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
snapshot.appendSections([.main])
snapshot.appendItems(items, toSection: .main)
dataSource.apply(snapshot, animatingDifferences: true)

Interview angle

A good answer acknowledges that the API reduces UI update bugs, but correctness still depends on stable identity and sane state modeling upstream.