gistfile1.swift

// works fine, but receiveValue may return on different threads
viewModel.$snapshot
    .sink { [weak self] snapshot in
        guard let self = self else { return }

        var animateDifferences = false

        switch self.viewModel.state {
        case .idle, .empty, .loading, .searching:
            animateDifferences = false

        case .loaded:
            animateDifferences = true
        }

        self.tableViewDataSource.apply(snapshot, animatingDifferences: animateDifferences)
    }
    .store(in: &cancellables)
  
  
// always calls apply on main thread, but table view gets laid out in an animation, expanding from (0, 0) origin to full width/height
viewModel.$snapshot
    .receive(on: DispatchQueue.main)
    .sink { [weak self] snapshot in
        guard let self = self else { return }

        var animateDifferences = false

        switch self.viewModel.state {
        case .idle, .empty, .loading, .searching:
            animateDifferences = false

        case .loaded:
            animateDifferences = true
        }

        self.tableViewDataSource.apply(snapshot, animatingDifferences: animateDifferences)
    }
    .store(in: &cancellables)

// works as expected with no table view layout animation, but required additional dispatch which feels gross, but always runs apply on the main thread
viewModel.$snapshot
    .sink { [weak self] snapshot in
        guard let self = self else { return }

        var animateDifferences = false

        switch self.viewModel.state {
        case .idle, .empty, .loading, .searching:
            animateDifferences = false

        case .loaded:
            animateDifferences = true
        }

        DispatchQueue.main.async {
          self.tableViewDataSource.apply(snapshot, animatingDifferences: animateDifferences)
        }
    }
    .store(in: &cancellables)