Begin forwarded message:
> From: Itai Ferber <[email protected]>
> Subject: Re: [swift-users] dealing with heterogenous lists/dictionary with
> Codable
> Date: October 19, 2017 at 9:39:25 AM PDT
> To: David Baraff <[email protected]>
> Cc: Geordie Jay <[email protected]>, swift-users <[email protected]>
>
> Hi David and Geordie,
>
> That approach won’t work — encoders and decoders only work directly with
> concrete Codable types (e.g. String, Int, MyFoo [where MyFoo is Codable],
> etc.).
> This is by design: since there is no type information stored in the JSON
> payload, there isn’t necessarily a way to tell how to decode the type you’re
> looking at, so asking for a generalCodable` isn’t helpful.
>
> Since it’s unlikely that what you truly need is a [String : Any] but really a
> [String : <one of String, Int, MyFoo, etc.>], one easy way to decode this
> type is to create a wrapper enum or similar which overrides init(from:) to be
> able to decode from one of those types. You can then ask to decode a [String
> : MyWrapperType] and use that instead.
>
> What types are you expecting in the dictionary?
>
>
The problem is that I want to be able to encode types T where
(a) T is String, Int
(b) lists of T
(c ) dictionaries of type <String, T>
The problem is the recursive nature: yes, my types are simple (say only base
types String and Int) but the “nesting” level may be quite deep (a list of list
of dictionaries of <etc.).
Let’s turn this around: in addition to the JSONEncoder, one can also use the
PropertyListEncoder.
Are we saying that something one could pull from a property list file (which is
pretty much what i want: arbitrary deep nesting of basic types) is also not
Codable? So a PropertyListEncoder could not encode actual property lists?
I really do want a heterogenous container. I think I am stuck.
> — Itai
>
> On 19 Oct 2017, at 18:11, David Baraff via swift-users wrote:
>
> I’ll try. Is that cast smart enough to apply recursively? We shall see.
>
> Sent from my iPad
>
> On Oct 19, 2017, at 7:34 AM, Geordie Jay <[email protected]
> <mailto:[email protected]>> wrote:
>
>> I mean can you do something along the lines of
>>
>> let codableDict = stringAnyDict as? [String : Codable]
>>
>> ?
>>
>> I’m not at a computer to test it myself
>>
>>
>>
>>
>> David Baraff <[email protected] <mailto:[email protected]>> schrieb
>> am Do. 19. Okt. 2017 um 15:45:
>> That’s exactly what I want. The ironic part is that I got my dictionary by
>> decoding a Json file. If that’s where my dictionary came from, is there a
>> simple way of coercing the Json serialization routines to give me back
>> codables, rather than Anys?
>>
>>
>> Sent from my iPad
>>
>> On Oct 19, 2017, at 3:38 AM, Geordie Jay <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>>>
>>> David Baraff via swift-users <[email protected]
>>> <mailto:[email protected]>> schrieb am Do. 19. Okt. 2017 um 03:47:
>>> So I have simple structs like this:
>>>
>>> struct Library: Codable {
>>> let domain: String
>>> let unit: String
>>> }
>>>
>>> and it’s super-simple to serialize. Yay.
>>>
>>> But:
>>>
>>> struct LibraryGroup : Codable { // I wish...
>>> let libraries: [Library]
>>> let someDict: [String : Any]
>>> }
>>>
>>> I haven’t tried this, but is it possible to have a dictionary of [String :
>>> Codable] ? Because that’s exactly the type requirements you’re describing,
>>> no?
>>>
>>> Geordie
>>>
>>>
>>> So what I’m looking for is something where if the values in someDict are
>>> themselves Codable, I can serialize things, and if they’re not, I can’t.
>>> In my previous scheme, I was using NSKeyedArchiver to serialize everything,
>>> manualy, including someDict; in trying to switch to Codable I ran smack
>>> into the fact that Codable wants to know what all the types are, in advance.
>>>
>>> Am I just stuck? How do I get the best of both worlds, where the compiler
>>> can make use of the fact that it can see the data types of my structures,
>>> while still being able to serialize heterogenous data like is found in
>>> LibraryGroup?
>>>
>>> Is my only alternative to write a custom coder for LibraryGroup? Is there
>>> any hope I could teach Codable what to do with
>>> [String: Any]
>>>
>>> ?
>>>
>>>
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>
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