In the following code, I get an error on the line indicated (4th from the
bottom) that "Protocol 'APIEndPoint' can only be used as a generic constraint
because it has Self or associated type requirements” I understand this is
because the APIEndPoint protocol contains a type alias. However I don’t
understand why this means it can’t be used as a type? I simply want the init
method I’m defining to be able to accept any object/enum that conforms to the
APIEndPoint protocol.
protocol API {
static var baseUrl : String { get };
}
protocol APIEndPoint {
typealias ParentAPI : API
var path: String { get }
func urlString() -> String
}
extension APIEndPoint {
func urlString() -> String {
return ParentAPI.baseUrl + path;
}
}
extension NSURL {
convenience init(instance:APIEndPoint) { //error here
self.init(string:instance.urlString())!
}
}
If I change that line to `convenience init<T:APIEndPoint>(instance:T) {`then
there is no problem.
Also if I split the APIEndPoint protocol in 2, like so:
protocol APIEndPointBase {
var path: String { get }
func urlString() -> String
}
protocol APIEndPoint : APIEndPointBase {
typealias ParentAPI : API
}
Then the change the line with the error to:
convenience init(instance:APIEndPointBase) {
then there is also no error.
The ability to work around this error makes it seem like the error is
pointless. Even if I used the ParentAPI typealias with the protocol definition,
I don’t see why I can’t use it as I have in the first code segment. Why does
having Self or associated type requirements mean that the protocol can only be
used as a generic constraint?
Apologies if I have posted this incorrectly, this is the first time I’ve used a
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Jonathan_______________________________________________
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