I know comparing protocols doesn't make any sense but my situation is dictated by choices and decisions taken before me. A table view's data source is an array of RowViewModel.
protocol RowViewModel {}
there's nothing in there (yet) to make it even conform to Equatable. Then my table has different cells, all of which implement that protocol:
func getCells() -> [RowViewModel] {
var rows = [RowViewModel]()
rows.append(Cell1ViewModel())
rows.append(Cell2ViewModel())
rows.append(Cell3ViewModel())
return rows
}
Cell's view model:
class Cell1ViewModel: RowViewModel {
var cellTitle: String
...
}
This structure is convenient but it now shoots me in the back because I now need to calculate delta to send specific tableView indexes to insert / delete rows. To calculate delta I need RowViewModel to conform to Equatable, which is possible but seems like a workaround that defies the initial point of using this approach. I'd like to do something like this:
let oldList = rows
let newList = getCells()
let deltaAdded = newList.filter { !oldList.contains($0) }.compactMap { newList.firstIndex(of: $0) }
let deltaRemoved = oldList.filter { !newList.contains($0) }.compactMap { oldList.firstIndex(of: $0) }
What is the best practice here? Is there a way to write a comparison function for concrete types conforming to the RowViewModel?
CodePudding user response:
As I told in comment you would have something like:
class CellViewModel1: Equatable {
// classes need explicit equatable conformance.
static func == (lhs: CellViewModel1, rhs: CellViewModel1) -> Bool {
// your implementation
return true
}
}
enum RowViewModel: Equatable {
// enum automatically is Equatable as long as all cases have Equatable associated types
case cell1(CellViewModel1)
}
func test() {
let oldList = [RowViewModel]()
let newList = [RowViewModel]()
let deltaAdded = newList.filter { !oldList.contains($0) }.compactMap { newList.firstIndex(of: $0) }
let deltaRemoved = oldList.filter { !newList.contains($0) }.compactMap { oldList.firstIndex(of: $0) }
}
Notice that both enum and ViewModels must conform to Equatable
.
Still not 100% sure if this fits your necessities.