Hi Rex, > On Apr 10, 2017, at 12:48 PM, Rex Fenley via swift-evolution > <[email protected]> wrote: > > Forgive me if I'm missing something, this is a very large proposal and a lot > to parse through. I like how everything is designed as far as I can tell > except I'm not sure from this proposal how one would compose multiple > different types of Decoders against the same output type. For example, with > Location we have. > > // Continuing examples from before; below is automatically generated by the > compiler if no customization is needed. > public struct Location : Codable { > private enum CodingKeys : CodingKey { > case latitude > case longitude > } > > public init(from decoder: Decoder) throws { > let container = try decoder.container(keyedBy: CodingKeys.self) > latitude = try container.decode(Double.self, forKey: .latitude) > longitude = try container.decode(Double.self, forKey: .longitude) > } > } > > However, this initializer seems strictly tied to the `CodingKeys` set of > coding keys. From what it appears, if this was used to decode from JSON the > format would have to always be: > > { > "latitude" : 20.0 > "longitude" : 20.0 > } > > I have a use case we're on my client we began the process of switching from > one version of an API to another. In one version we had a payload similar to > > { > "user" : { > "uuid" : "uuid string..." > "can_send_message" : true > "can_delete_message" : false > } > } > > this would result in the following Codable (from "user") from what I'm > following > > public struct User : Codable { > private enum CodingKeys : CodingKey { > case uuid > case can_send_message > case can_delete_message > } > > public init(from decoder: Decoder) throws { > let container = try decoder.container(keyedBy: CodingKeys.self) > uuid = try container.decode(Double.self, forKey: .uuid) > canSendMessage = try container.decode(Bool.self, forKey: > .can_send_message) > canDeleteMessage = try container.decode(Bool.self, forKey: > .can_delete_message) > } > } > > when we began switching over to the new api the payload was returned as > > { > user { > "uuid" : "uuid string..." > "permissions" : { > "can_send_message" : true > "can_delete_message" : false > } > } > } > > Here with "permissions" we have a new internal container with a separate set > of coding keys. Issue is in my use case I still need to maintain a way to > decode the old version simultaneously; we guard all new changes behind > feature flags in case something goes awry and we need to roll back our > changes. > > How would one go about expressing this new Decoding and the previous Decoding > simultaneously on the same User type?
You would fall out of the automatically-generated scenario here, but this use case is exactly what the ‘container’ API is for. You can create a container with a new set of keys, then decode from it. Another approach would be to create a nested type that conforms with Codable which represents the “permissions” as a type of its own. - Tony > > > -- > Rex Fenley | IOS DEVELOPER > > > Remind.com <https://www.remind.com/> | BLOG <http://blog.remind.com/> | > FOLLOW US <https://twitter.com/remindhq> | LIKE US > <https://www.facebook.com/remindhq>_______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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