Protocol with associatedtype conformance with generic gives compiler error - swift

Question

I'm trying to make a DB mock to test some UI implementations, but compiler keeps giving me the following error:
Type 'DBClientMock<T>' does not conform to protocol 'DBClient'
This is my code...
protocol DBClient {
associatedtype Model
func get(id: UUID, completion: #escaping ((Model?, Error?)) -> Void)
func insert(_ model: Model, completion: #escaping (Error?) -> Void)
func delete(_ model: Model, completion: #escaping (Error?) -> Void)
}
final class DBClientMock<T>: DBClient where T: Identifiable, T: Equatable {
typealias Model = T
private let queue: DispatchQueue
private var modelDB = [T]()
enum Error: Swift.Error {
case notFound
}
init(queue: DispatchQueue = DispatchQueue.global()) {
self.queue = queue
}
private func getModel(id: UUID) -> T? {
let results = modelDB.filter({ $0.id as? UUID == id })
guard results.count > 0 else { return nil }
return results[0]
}
// Extension
func get(id: UUID, completion: #escaping ((T?, Error?)) -> Void) {
let record = getModel(id: id)
queue.asyncAfter(deadline: .now() + .milliseconds(1500), execute: {
if let model = record {
completion((model, nil))
} else {
completion((nil, Error.notFound))
}
})
}
func insert(_ model: T, completion: #escaping (Error?) -> Void) {
modelDB.append(model)
queue.asyncAfter(deadline: .now() + .milliseconds(1000), execute: {
completion(nil)
})
}
func delete(_ model: T, completion: #escaping (Error?) -> Void) {
modelDB.removeAll(where: { $0 == model })
queue.asyncAfter(deadline: .now() + .milliseconds(800), execute: {
completion(nil)
})
}
}
XCode: Version 12.4 (12D4e)
Swift: 5.0
What am I doing wrong? Do I have to be more explicit with the generic type in some way? I tried replacing T with Model but had the same result.
Thanks for your help!

Answer 1

It doesn't conform because you declared another Error type inside the class, so everywhere where you use Error in the required methods, it uses DBClientMock.Error instead of the protocol-required Swift.Error.
Either rename DBClientMock.Error to something else, or change the Error in methods to Swift.Error, like below:
// Extension
func get(id: UUID, completion: #escaping (T?, Swift.Error?) -> Void) {
//...
}
func insert(_ model: T, completion: #escaping (Swift.Error?) -> Void) {
//...
}
func delete(_ model: T, completion: #escaping (Swift.Error?) -> Void) {
//...
}