Extension of protocol cannot have an inheritance clause

Question

I'm trying to create filter functionality using Swift. I have many filter types like Location, Skill, etc. So I'm planning to generalize this using a protocol.

protocol FilterProtocol {
    var text: String { get set }
    var count: String? { get set }
    var isSelected: Bool { get set }
}

extension FilterProtocol: Identifiable {
    var id: String  { text }
}

struct LocationFilter: FilterProtocol {
    var text: String
    var count: String?
    var isSelected: Bool
}

But I am getting error Extension of protocol 'FilterProtocol' cannot have an inheritance clause

Do not make a substantial change to your question after it has already been answered. Simply ask another question — Paulw11, Jun 29 '22 at 12:12
Can't figure out why sometimes swift allows it and other times it doesn't. I added a protocol extension in a file, built ran with no problem. Moved it to a separate file and then the error :( — Mercutio, Jul 01 '22 at 16:59

Asperi · Answer 1 · 2022-06-29T11:48:19.683

Just move the conformance to the declaration:

protocol FilterProtocol: Identifiable {
    var text: String { get set }
    var count: String? { get set }
    var isSelected: Bool { get set }
}

extension FilterProtocol {
    var id: String  { text }
}

another variant if we consider to make just provided part of code compilable... there might be many variants (depending on final needs and that's out of topic):

protocol FilterProtocol {
    var text: String { get set }
    var count: String? { get set }
    var isSelected: Bool { get set }
}

extension FilterProtocol {      // << just extension
    var id: String  { text }
}

struct LocationFilter: FilterProtocol {
    var text: String
    var count: String?
    var isSelected: Bool
}

struct FilterView: View {

    let filters: [FilterProtocol] = []   // << non-generic

    var body: some View {
        VStack(alignment: .leading) {
            HStack {
                Text("By Location")
                    .font(.headline)
                Spacer()
                Button(action: {}) {
                    Image(systemName: "arrowtriangle.down.circle")
                }
            }
            ForEach(filters, id: \.id) { filter in  // << explicit .id
                HStack {
                    Text(filter.text)
                    Text(filter.count ?? "")

                }
            }
        }.padding()
    }
}

Thanks Asperi, Error gone but how can I `Equatable` extension, I'm getting error again — user8719510, Jun 29 '22 at 11:41
Thank you very much for detail example. without Protocol can I simple make `struct` Implementation, see my Edited Question. — user8719510, Jun 29 '22 at 11:51

Extension of protocol cannot have an inheritance clause

1 Answers1