Swift Users:
I have a generics use case which has somewhat stumped me. I have two
related protocols, JSONDecodable and CompressedDecodable, and
CompressedDecodable inherits from JSONDecodable (though that relationship isn’t
strictly necessary). I also have a generic function that’s overloaded for each
of those protocols. I’m trying to write a class to make a network request
expecting a generic response type of either JSONDecodable or
CompressedDecodable. However, it doesn’t seem possible to write it in such a
way that the overload I need is called. Instead, it’s always the superclass’
type’s overload that is called. For example:
protocol JSONDecodable { init() }
protocol CompressedDecodable: JSONDecodable { }
class NetworkRequest<T: JSONDecodable> {
var response: T?
func doAThing() {
response = doSomething()
}
}
class CompressedNetworkRequest<U: CompressedDecodable>: NetworkRequest<U> {
}
func doSomething<T: JSONDecodable>() -> T {
print("One: \(T.self)")
return T()
}
func doSomething<T: CompressedDecodable>() -> T {
print("Two: \(T.self)")
return T()
}
struct Uno: JSONDecodable { }
struct Dos: CompressedDecodable { }
NetworkRequest<Uno>().doAThing()
CompressedNetworkRequest<Dos>().doAThing()
In a playground this prints:
One: Uno
One: Dos
Ultimately, I understand why this happens (NetworkRequest’s generic type is
always going to be JSONDecodable, no matter if it’s actually a subtype). Is
there any way, aside from completely duplicating the class, to call the
overload appropriate for the type passed in a class like this?
Jon Shier
_______________________________________________
swift-users mailing list
swift-users@swift.org
https://lists.swift.org/mailman/listinfo/swift-users
