[swift-evolution] [Proposal] Foundation Swift Archival & Serialization

[Ben Rimmington]

> On 23 Mar 2017, at 19:37, Ben Rimmington wrote:
> 
>> On 22 Mar 2017, at 17:41, Itai Ferber wrote:
>> 
>> What’s the use case that you were thinking of? KeyPaths could be useful in the case where you don’t need to customize your key names, but cannot represent a custom case like
>> 
>> public struct Post {
>>     var authorID: Int
>>     var bodyText: String
>> 
>>     private enum CodingKeys : String, CodingKey {
>>         case authorID = "author_id"
>>         case bodyText = "body_text"
>>     }
>> }
>> Or am I misunderstanding?
>> 
> 
> For custom names, the `CodingKeys` enum does seem like the best design, unless an attribute can be used.
> 
> 	public struct Post : Codable {
> 	    @codable(name: "author_id") var authorID: Int
> 	    @codable(name: "body_text") var bodyText: String
> 	}
> 
> If each `KeyPath` encapsulates the type information, the `decode` methods won't need a `type` parameter.
> 
> 	/// Primitive decoding methods (for single-value and keyed containers).
> 	open class DecodingContainer<Root : Codable> {
> 	    open func decode(for keyPath: KeyPath<Root, Bool>)   throws -> Bool
> 	    open func decode(for keyPath: KeyPath<Root, Int>)    throws -> Int
> 	    open func decode(for keyPath: KeyPath<Root, UInt>)   throws -> UInt
> 	    open func decode(for keyPath: KeyPath<Root, Float>)  throws -> Float
> 	    open func decode(for keyPath: KeyPath<Root, Double>) throws -> Double
> 	    open func decode(for keyPath: KeyPath<Root, String>) throws -> String
> 	    open func decode(for keyPath: KeyPath<Root, Data>)   throws -> Data
> 	}
> 
> 	/// Keyed containers inherit the primitive decoding methods.
> 	open class KeyedDecodingContainer : DecodingContainer {
> 	    open func decode<Value : Codable>(for keyPath: KeyPath<Root, Value>) throws -> Value
> 	}

On second thought, "property behaviors" <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170313/034042.html> could eventually allow the custom name to be stored in a `KeyPath` subclass.

Key paths would also need `LosslessStringConvertible` conformance. The current design only has `CustomDebugStringConvertible` conformance.

-- Ben

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