1 
protocol ToTableRow {
    associatedtype TableRow: IsTableRow
    func toTableRow() -> TableRow
}
protocol IsTableRow {
    associatedtype Model
}

// Removing the where clause will cause the code to no longer compile
class TableVM<Model: ToTableRow, TableRow: IsTableRow> where TableRow == Model.TableRow {
    var model: [Model]
    var tableRows: [TableRow]

    init(model: [Model]) {
        self.model = model
        self.tableRows = model.map({ $0.toTableRow() })
    }
}

Xcode tells me: Redundant conformance constraint 'TableRow': 'IsTableRow'

Reality: definitely not redundant :)

edit: I've come to realize it's telling me I can remove : IsTableRow from TableRow, because the where clause makes it redundant I suppose. I don't know that that's good however - because then it is no longer clear that TableRow is constrained in any way, without looking at the implementation of the ToTableRow protocol

2

I’ve moved this topic to the Using Swift category, since it didn’t belong in Compiler Development.

• • •

Regarding your code, you don’t need two generic parameters on the class, only one:

class TableVM<Model: ToTableRow> {
  var model: [Model]
  var tableRows: [Model.TableRow]
  ⋮
}

If you want the shorthand of writing TableRow instead of Model.TableRow you can simply define a typealias in the class.

1 Like
3

I was surprised to find your version compiling - it only works when there is a unique TableRow, for a Model.