CODEWITHSUNDEEP
swiftswift-protocols
WishIHadThreeGuns
WishIHadThreeGuns

Reputation: 1469

Cast a protocol to another protocol Swift

I am trying to work with protocols across Pods. I have then simplified by problem here so I can ask a question on StackOverflow.

In my problem TestClass does not know anything about SecondProtocol (as it is in a separate pod). 

public protocol FirstProtocol {
    func get(data: String) -> String
}

public protocol SecondProtocol {
    func get(data: String) -> String
}

class TestClass {
    func get(data: String) -> String {
        return "Rest data"
    }

    public init() { }
}

extension TestClass : FirstProtocol {}

let myTest : FirstProtocol?

myTest = TestClass() as FirstProtocol

let secondTest: SecondProtocol?

secondTest = myTest as! SecondProtocol

So the last line causes a crash in Swift. In a sense, I understand why. However secondTest is instantiated from the main program rather than the Pod secondTest, so SecondTest knows nothing about SecondProtocol. Yet a second pod expects an input of Second Protocol.

So how can I get secondTest to cast to SecondProtocol?

Upvotes: 0

Views: 438

Answers (1)

fphilipe
fphilipe

Reputation: 10054

All you're missing is to make TestClass conform to SecondProtocol, just like you did for FirstProtocol:

extension TestClass : SecondProtocol {}

You can specify protocol conformances for classes, structs, and enums that are defined in other modules, such as in Foundation or UIKit as well as in third party dependencies.

Upvotes: 4

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