My apologies. I misstated the problem: I don’t want to just limit to Int,
String, [Int], etc. but also allow structures where
struct NewThingy : Codable {
let data1: T1
let data2: T2
}
where T1 and T2 are themselves Codable.
So basically, back to wanting to let the compiler do the work, when I make new
structures, while still allowing for heterogenous containers.
Begin forwarded message:
> From: Itai Ferber <ifer...@apple.com>
> Subject: Re: [swift-users] dealing with heterogenous lists/dictionary with
> Codable
> Date: October 19, 2017 at 10:40:28 AM PDT
> To: David Baraff <davidbar...@gmail.com>
> Cc: Geordie Jay <geo...@gmail.com>, swift-users <swift-users@swift.org>
>
> Why are you stuck? I think the following matches your needs, no?
>
> import Foundation
>
> enum MyType : Codable, Equatable {
> case int(Int)
> case string(String)
> case list([MyType])
> case dictionary([String : MyType])
>
> public init(from decoder: Decoder) throws {
> // Can be made prettier, but as a simple example:
> let container = try decoder.singleValueContainer()
> do {
> self = .int(try container.decode(Int.self))
> } catch DecodingError.typeMismatch {
> do {
> self = .string(try container.decode(String.self))
> } catch DecodingError.typeMismatch {
> do {
> self = .list(try container.decode([MyType].self))
> } catch DecodingError.typeMismatch {
> self = .dictionary(try container.decode([String :
> MyType].self))
> }
> }
> }
> }
>
> public func encode(to encoder: Encoder) throws {
> var container = encoder.singleValueContainer()
> switch self {
> case .int(let int): try container.encode(int)
> case .string(let string): try container.encode(string)
> case .list(let list): try container.encode(list)
> case .dictionary(let dictionary): try container.encode(dictionary)
> }
> }
>
> static func ==(_ lhs: MyType, _ rhs: MyType) -> Bool {
> switch (lhs, rhs) {
> case (.int(let int1), .int(let int2)): return int1 == int2
> case (.string(let string1), .string(let string2)): return string1 ==
> string2
> case (.list(let list1), .list(let list2)): return list1 == list2
> case (.dictionary(let dict1), .dictionary(let dict2)): return dict1
> == dict2
> default: return false
> }
> }
> }
>
> let values: MyType = .list([.int(42), .string("hello!"), .list([.int(9),
> .string("hi")]), .dictionary(["zero": .int(0), "one": .int(1)])])
> print(values)
>
> let encoder = JSONEncoder()
> let data = try encoder.encode(values)
> print(String(data: data, encoding: .utf8)!) // =>
> [42,"hello!",[9,"hi"],{"zero":0,"one":1}]
>
> let decoder = JSONDecoder()
> let decoded = try decoder.decode(MyType.self, from: data)
> print(decoded)
>
> print(values == decoded) // => true
> On 19 Oct 2017, at 20:15, David Baraff wrote:
>
> Begin forwarded message:
>
>> From: Itai Ferber <ifer...@apple.com <mailto:ifer...@apple.com>>
>> Subject: Re: [swift-users] dealing with heterogenous lists/dictionary with
>> Codable
>> Date: October 19, 2017 at 9:39:25 AM PDT
>> To: David Baraff <davidbar...@gmail.com <mailto:davidbar...@gmail.com>>
>> Cc: Geordie Jay <geo...@gmail.com <mailto:geo...@gmail.com>>, swift-users
>> <swift-users@swift.org <mailto:swift-users@swift.org>>
>>
>> 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 <geo...@gmail.com
>> <mailto:geo...@gmail.com>> 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 <davidbar...@gmail.com <mailto:davidbar...@gmail.com>> 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 <geo...@gmail.com
>>> <mailto:geo...@gmail.com>> wrote:
>>>
>>>>
>>>> David Baraff via swift-users <swift-users@swift.org
>>>> <mailto:swift-users@swift.org>> 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]
>>>>
>>>> ?
>>>>
>>>>
>>>> _______________________________________________
>>>> swift-users mailing list
>>>> swift-users@swift.org <mailto:swift-users@swift.org>
>>>> https://lists.swift.org/mailman/listinfo/swift-users
>>>> <https://lists.swift.org/mailman/listinfo/swift-users>
>>
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>
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