Following swift code gives the Protocol 'DataSource' can only be used as a generic constraint because it has Self or associated type requirements
error. How can it be fixed?
protocol DataSource {
associatedtype DataItem
func getItem(at index: Int) -> DataItem
}
struct DataSourceAgent: DataSource {
typealias DataItem = Int
func getItem(at index: Int) -> DataItem {
return 0
}
}
class SomeClass<T> {
private var dataSource: DataSource!
init(dataSource: DataSource) {
self.dataSource = dataSource
}
func getSomeStuff() -> T {
return dataSource.getItem(at: 0)
}
}
let sc = SomeClass<Int>(dataSource: DataSourceAgent())
You can't use a protocol with associated type the same way as you would use normal protocol, but you can use DataSource
as type constraint in SomeClass
in this way:
class SomeClass<T, D:DataSource> where D.DataItem == T {
private let dataSource:D
init(dataSource: D) {
self.dataSource = dataSource
}
func getSomeStuff() -> T {
return dataSource.getItem(at: 0)
}
}
let sc = SomeClass<Int, DataSourceAgent>(dataSource: DataSourceAgent())
print(sc.getSomeStuff())