Extend emun case

Question

craigaps OP

Created Oct ’19

Replies 6

Boosts 0

Views 1.5k

Participants 4

Hi

I'm using enum and wanted to write an extension to expose additional case values. Just confirming that this is not possible in Swift 5.1. I was thinking something like:

import CryptoKit

extension CryptoKitError {
    enum `Self` : Error {
    /// The data used to deserialized a key with `SecKeyCreateWithData` was incorrect.
    case incorrectKeyData
    
    /// The generation of the failed.
    case keyFailure
    }
}

The closest usage I example is:

throw CryptoKitError.Self.keyFailure

What I'd really want is:

throw CryptoKitError.keyFailure

Thanks

Answered by Claude31 in 388886022

I find it logical, as enum extension is defined as properties of Self.

You cannot extend enum directly with:

extension CryptoKitError { 
    case incorrectKeyData 
    case keyFailure 
}

Boost

Answer 1

Claude31 OP

Oct ’19

Accepted Answer

I find it logical, as enum extension is defined as properties of Self.

You cannot extend enum directly with:

extension CryptoKitError { 
    case incorrectKeyData 
    case keyFailure 
}

0

Answer 2

craigaps OP

Oct ’19

Hi

I thought that might be the case that I couldn't extend an enum directly.

0

Answer 3

Claude31 OP

Oct ’19

That could be worth a question on Swift.org.

Don't forget to close this thread anyway.

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Answer 4

craigaps OP

Oct ’19

yep, no worries

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Answer 5

ZaBlancii OP

Oct ’19

I can't imagine this ever being possible because of all the existing code designed to address every possible outcome in a switch/case. Suddenly none of it would be exhaustive. It would break all of that.

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Answer 6

DTS Engineer OP

Apple

Oct ’19

I can't imagine this ever being possible because of all the existing code designed to address every possible outcome in a switch/case. Suddenly none of it would be exhaustive. It would break all of that.

Swift has the facilities to deal with that in some cases. See SE-0192 Handling Future Enum Cases. However, this only allows the original enum declaration to add new cases. craigaps is trying to add new cases in an extension, something that’s not currently possible. Adding such a feature is not beyond the realm of possibility, although such discussions are best held on Swift Evolution.

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