[swift-users] dealing with heterogenous lists/dictionary with Codable

Itai Ferber iferber at apple.com
Thu Oct 19 15:29:34 CDT 2017

Mm, the point I’m trying to get at here is that JSON is inherently 
untyped while Swift is strongly typed, and the two don’t line up.
It doesn’t really make sense to ask to decode an existential because 
there’s not enough type information to influence what you get back.

On 19 Oct 2017, at 13:20, David Sweeris wrote:

> I think if you can figure that out, you’re halfway to letting 
> protocols conform to themselves.
> (Syntactically, I would probably say that something like 
> “Codable.Self” would read well, but I think that already means 
> something. Maybe the answer will become clearer when we rework the 
> reflection APIs?)
> Sent from my iPhone
>> On Oct 19, 2017, at 13:13, Itai Ferber <iferber at apple.com> wrote:
>> Even then, that wouldn’t necessarily help in the general case. If 
>> you decode {"key" : 1} as [String : Codable], what concrete type 
>> would 1 have? Int? Double? Int8? (Arguments can be made for any one 
>> of these, but the key here is that it is inherently ambiguous and 
>> there isn’t necessarily a good answer.)
>> On 19 Oct 2017, at 12:57, David Sweeris wrote:
>> On Oct 19, 2017, at 12:50 PM, David Baraff via swift-users 
>> <swift-users at swift.org> wrote:
>> Yes; this is a case where anywhere in the code base I want to just 
>> say
>> struct MyNewType : Codable {
>> // add codable datatypes
>> }
>> and don’t want/can’t always go to the centralized place to add it 
>> in.
>> Is there some extension-like trick I can pull off that lets me spread 
>> the implementation out over different files/libraries?
>> Ah, ok.
>> No, I don't think you'll be able to do that until/unless Swift gets 
>> more macro/metaprogramming features. Maybe if protocols ever get to 
>> conform to themselves? That's a common request, but implementing it 
>> is apparently beyond tricky. I'm pretty sure somebody's working on 
>> it, but "bigger fish" and all that...
>> - Dave Sweeris

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-users/attachments/20171019/a6868cbe/attachment.html>

More information about the swift-users mailing list