Unexpected behavior

[ericlewis]

Hey all, I was just trying something out and ran into an odd issue. I am not entirely sure what the compiler is thinking.

The below code has a problem when it comes to decoding, with JSONDecoder throwing Expected to decode Array<Any> but found a dictionary instead. on files, what is interesting is if we change the type to: [String: File] it works perfectly fine. I didn't dig in to it much, but it seems like the ExpressibleByArrayLiteral conformance is being interpreted incorrectly.

Problem code:

struct Gist {
  let id: Self.ID
  let files: [File.Name: File]

  typealias ID = Tagged<Self, String>
}

extension Gist: Identifiable {}
extension Gist: Codable {}

struct File {
  let filename: Name
  let content: String

  typealias Name = Tagged<Self, String>
}

extension File: Codable {}

[stephencelis]

Hi @ericlewis! There doesn’t appear to be any decoding code in your example above that would throw. Can you provide a full sample that reproduces the issue? There are definitely some gotchas around codability, some of which we can’t work around when it comes to coding containers, but if there is a bug we can fix we’d love to know!

[mbrandonw]

This is currently a Swift limitation in which only string and integer keys properly encode/decode into dictionaries. A fix has been proposed and accepted into Swift: https://github.com/apple/swift-evolution/blob/main/proposals/0320-codingkeyrepresentable.md

[ericlewis]

Ah! Seems like that is the case then @mbrandonw.

[ericlewis]

@stephencelis it just using a JSONDecoder.decode(Gist.self, from: data). Nothing fancy. Brandon's reply seems to be the case.

[stephencelis]

@ericlewis That was one of the issues around decoding containers I was alluding to, just wanted to confirm what data was beforehand :)