I have 3 model classes:
protocol IncludedItem {
var id: Int { get }
var text: String { get }
}
protocol PrimaryItem {
associatedtype Included: IncludedItem
var id: Int { get }
var canClose: Bool { get }
var canDelete: Bool { get }
var canSend: Bool { get }
var includedItems: [Included] { get }
}
protocol QuoteItem {
var id: Int { get }
var isSelectable: Bool { get }
}
Then I want to use the factory pattern for Item creation. This is my factory protocol:
protocol QuoteItemFactory {
associatedtype Item: PrimaryItem
var delegate: QuoteItemFactoryDelegate? { get set }
func create(item: Item) -> QuoteItem
}
And this is an implementation of the factory protocol:
class OrderQuoteItemFactory: QuoteItemFactory {
weak var delegate: QuoteItemFactoryDelegate?
func create<Item: PrimaryItem>(item: Item) -> QuoteItem {
let viewModel = OrderQuoteViewModel(quote: item)
viewModel.delegate = self
return DefaultQuoteItem.quote(id: item.id, viewModel: viewModel)
}
}
But then I always get the following error:
Type 'OrderQuoteItemFactory' does not conform to protocol 'QuoteItemFactory'.
What am I doing wrong? I know if I use it like this:
class OrderQuoteItemFactory<Item: PrimaryItem>: QuoteItemFactory {
weak var delegate: QuoteItemFactoryDelegate?
func create(item: Item) -> QuoteItem {
let viewModel = OrderQuoteViewModel(quote: item)
viewModel.delegate = self
return DefaultQuoteItem.quote(id: item.id, viewModel: viewModel)
}
}
I know that using it like this will work perfectly. But I’m wondering why I can’t use the generic with the function declaration.
>Solution :
What if you change your factory protocol to this?
protocol QuoteItemFactory {
var delegate: QuoteItemFactoryDelegate? { get set }
func create<Item: PrimaryItem>(item: Item) -> QuoteItem
}
I noticed (at least from your example) that you don’t really need an associatedType, so you could just make the function itself generic, instead of the protocol.