1

Consider this enum protocol conformance structure.

enum topA:midA{}
enum topB:midB{}
protocol midA:bottom{}
protocol midB:bottom{}
protocol bottom{}

Store a mix of topA's and topB's in a collection as bottom's.

On retrieval, I need to know if the stored enum is a midA or a midB.

I've tried as

if stored as? midA != nil
if stored as? midA.Type != nil
and
if stored is midA

None of these approaches allow me to differentiate between stored midA's and stored midB's. They all fail.

How can I find out which protocol the stored item conforms to?

Thanks.

2

Can you show how you store the values in your collection? For example, the following works for me as expected with Swift 5.9:

protocol Bottom {}
protocol MidA: Bottom {}
protocol MidB: Bottom {}
enum TopA: MidA { case a }
enum TopB: MidB { case b }

let values: [any Bottom] = [
  TopA.a,
  TopB.b,
  TopA.a,
  TopB.b,
] 

for value in values {
    if value is MidA {
        print("MidA: \(value)")
    } else if value is MidB {
        print("MidB: \(value)")
    } else {
        print("Unknown: \(value)")
    }
}

// Prints:
// MidA: a
// MidB: b
// MidA: a
// MidB: b
1 Like
3

To add to what itaiferber said, if you also need the element cast to that type you can do

for value in values {
    if let a = value as? MidA {
        print(type(of: a))
    } else if let b = value as? MidB {
        print(type(of: b))
    } else {
        print("Unknown: \(value)")
    }
}

Edit: oops, the print(type(of:)) isn’t actually proof it’s that cast type but a is actually any MidA and b is any MidB

4

It’s not the individual enigma that end up being stored, but the types. I apologize for not mentioning this in the original posting. The enigma are being used as namespaces for static public functions.

I need to be able to tell the type of the protocol the final enum type implements.

Thanks.

1 Like
5

That would be enums not enigmas. Dang spell checker.

1 Like
6

It's not 100% clear to me what you mean — is it something like this?

let types: [any Bottom.Type] = [
    TopA.self,
    TopB.self,
    TopA.self,
    TopB.self,
]

Because if so, you would replace value is <Protocol> with type is <Protocol>.Type:

for type in types {
    if type is MidA.Type {
        print("\(type) is MidA")
    } else if type is MidB.Type {
        print("\(type) is MidB")
    } else {
        print("Unknown \(type)")
    }
}

// Prints:
// TopA is MidA
// TopB is MidB
// TopA is MidA
// TopB is MidB

If this isn't what you meant, do you mind sharing code showing exactly what you're doing?

7

I can when I get back to work Monday.

Thanks.

8

I found a typo in the complicated code not included here. The simplified code works well. My eyeballs just slid over the typo. Sorry to take up your time. Thanks very much.

1 Like