ezfe
(Ezekiel Elin)
1
Here's my sample code. I'm trying to create a function builder that generates ContainerType 's with some unrelated-type input. In the sample code, I'm using a boolean (my actual code is parsing raw data).
protocol ProtocolType {
}
struct ConformingA: ProtocolType {
}
struct ConformingB: ProtocolType {
}
struct ContainerType<E> where E: ProtocolType {
let contents: E
init(contents: E) {
self.contents = contents
}
}
func make(from bool: Bool) -> ContainerType<???> {
if bool {
return ContainerType(contents: ConformingA())
} else {
return ContainerType(contents: ConformingB())
}
}
Where I've put the ??? is the point where it stops working. If I write any ProtocolType (which is my interpretation of what I need) I get the following error:
Type 'any ProtocolType' cannot conform to 'ProtocolType'
1 Like
To return different specialized types of ContainerType you have to type erase the containers:
protocol ContainerProtocol {
associatedtype E: ProtocolType
var contents: E { get }
}
struct ContainerType<E>: ContainerProtocol where E: ProtocolType {
let contents: E
init(contents: E) {
self.contents = contents
}
}
func make(from bool: Bool) -> any ContainerProtocol {
if bool {
return ContainerType(contents: ConformingA())
} else {
return ContainerType(contents: ConformingB())
}
}
1 Like
ezfe
(Ezekiel Elin)
3
Aha, that's what I was missing - I understood I needed to somehow erase the generic type but it never occurred to me to do that with another protocol.
