If you need multiple different representations for multiple different
formats, then yes, you will likely want to supply different `CodingKeys`
enums for those formats and write a custom encode which switches on the
format you're writing to. Or, you can use one `CodingKeys` enum which
has multiple different key representations (for the different formats
you want to support) and use that.
Automatic key renaming is an inherently unsafe operation, so it's not
something that we want to provide out of the box, or encourage, but it
should be possible if you really want it.
On 1 May 2017, at 13:04, Anders Ha wrote:
I do mean optional automatic translation on the encoders’ and
decoders’ end though. Derived conformances from other common naming
conventions are nice to have, but does not help if one wants to define
a model that can be decoded from and encoded into different coded
representations of itself. It also “hardwired" the model with a
specific coding scheme, which does not seem very nice from an
encapsulation PoV.
That said I am fairly sure there would be third party libraries
providing key mapping/transformation, if Foundation’s encoders and
decoders do not provide such functionality. So it is probably not a
big deal.
Regards
Anders
On 2 May 2017, at 3:06 AM, Itai Ferber <[email protected]> wrote:
Sorry, one clarifying statement: it's not the JSON encoder and
decoder that will be providing this renaming (since they should be
encoding the key values they are given as-is); the key names are part
of the definition of the enum, as declared as part of the type.
On 1 May 2017, at 12:04, Itai Ferber via swift-evolution wrote:
Yes, this should be true for most types.
The compiler derives conformance based on a nested CodingKeys type
within your Codable type. If you do not supply one, it will derive
one on your behalf, but if you do provide one, making a naming
transition like this is trivial:
public struct Post
: Codable {
let authorID: Int
let authorName: String
let bodyText: String
private enum CodingKeys: String
, CodingKey {
case authorID = "author_id"
case authorName = "author_name"
case bodyText = "body_text"
}
// init(from:) and encode(to:) are still automatically generated
}
This is something we wanted to explicitly support as we don't want
users to have to violate Swift naming guidelines, and is a step along
the progressive disclosure of the API that we want to provide.
As long as the case names of the enum match 1-to-1 with property
names, derived conformance still applies.
On 1 May 2017, at 11:39, Anders Ha wrote:
I thought it would be quite trivial to have the JSON encoder and
decoder transforming the keys between camel case and snake case,
wouldn't it?
Regards
Anders
On 2 May 2017, at 1:57 AM, Jon Shier via swift-evolution
<[email protected]> wrote:
FYI, I’d give the derived implementations a very low chance of
ever being used for JSON. Unless developers violate the Swift naming
guidelines for their properties at least or they don’t have
properties with multiword keys.
Once this functionality has landed for the Swift 4 branch, I plan
to implement some of the tricky JSON types I had to decode on a
recent project, just to see how painful the custom syntax will be,
and to compare it to my existing Argo implementation. Hopefully
there will be time for at least one round of feedback to be
integrated into this functionality.
Jon
On May 1, 2017, at 12:54 PM, Itai Ferber via swift-evolution
<[email protected]> wrote:
Hi Goffredo,
On Apr 26, 2017, at 2:00 PM, Goffredo Marocchi <[email protected]>
wrote:
Hello Itai,
Sorry for the confusion, but I understood that the following
To answer your second question, the reason is that using the
protocol implies that all encoders and decoders must support
anything that conforms to that protocol. We’re not sure this is
a reasonable requirement. Many formats do not have any kind of
support for arbitrary size integers, for example. Therefore, we
felt it was best to limit it to a set of concrete types.
meant it would actually hinder that kind of transformation or make
it more difficult to write custom decoders and encoders. Sorry if
I misunderstood that.
One follow up question: what would happen if inside the JSON mock
object you posted I were to remove the 'address' key (in terms of
the produced object and how to access its inner properties)?
What would happen if I remove the 'name' one or better if I add
another key to the JSON object?
Codable conformance is derived by default to require that all
non-optional properties be initialized. This means that if you have
a non-optional property address: Address but there is no address
key in the JSON payload you're decoding from, it will throw an
error to indicate that the key was not found.
On the flip side, if the JSON payload has information in it which
your type does not have (e.g. if there is an address in the JSON,
but your Person just has name), the extra data is ignored.
This, however, is just in the default, derived conformance. For
more complex cases, you can always provide your own init(from:) and
encode(to:)to do custom decoding. If you have a property which may
or may not be in the JSON, you can always decodeIfPresent, which
will return nil if the key or value was not found.
If you need to access sub-objects in the JSON data which do not map
to your properties 1-to-1, e.g. your payload looks like {"name":
"John Doe", "address": { "street": "1 Infinite Loop", ... } }, but
your type looks like
struct Person {
let name: String
let street: String
let city: String
// ...
}
then you can always access the nested data by requesting a
nestedContainer(keyedBy: ..., forKey: .address) which will return a
container wrapping the address sub-object, which you can then pull
fields out of.
The derived conformance case gives a reasonable default, but you
can always write your own init(from:) and encode(to:) to handle
custom needs.
Sent from my iPhone
On 26 Apr 2017, at 21:28, Itai Ferber <[email protected]> wrote:
Hi Goffredo,
Unless I'm misunderstanding what you mean here, this is exactly
what we're proposing with the API — anything Encodable can
encode any type that is Encodable as a nested value:
struct Person
: Codable {
let name: String
let address
: Address
}
struct Address
: Codable {
let street: String
let city: String
let state: String
let zipCode: Int
let country: String
}
let address = Address(street: "1 Infinite Loop", city:
"Cupertino", state: "CA", zipCode: 95014, country: "United
States"
)
let person = Person(name: "John Doe"
, address: address)
let encoder
= JSONEncoder()
let payload
= try encoder.encode(person)
print(String(data: payload, encoding: .utf8)!) // => {"name":
"John Doe", address: {"street": "1 Infinite Loop", ... } }
let decoder
= JSONDecoder()
let decoded = try decoder.decode(Person.self, from: payload) //
=> Person(name: "John Doe", address: ...)
Or have I misunderstood you?
— Itai
On 26 Apr 2017, at 13:11, Goffredo Marocchi via swift-evolution
wrote:
Sent from my iPhone
On 26 Apr 2017, at 17:24, Tony Parker via swift-evolution
<[email protected]> wrote:
Hi Riley,
On Apr 25, 2017, at 6:11 PM, Riley Testut via swift-evolution
<[email protected]> wrote:
I’m sure this has already been discussed, but why are the
methods throwing NSErrors and not Enums? If I’m remembering
correctly, the original reason for this was because this was
meant to be a part of Foundation. Now that this is in the
Standard Library, however, it seems strange that we’re still
using NSError.
Second question that again I’m sure was asked and answered
already, but: why do we require implementations for each
concrete numeric type (Int, Int8, Int16, Float, etc), instead
of using protocols (such as the new Integer protocols)?
To answer your second question, the reason is that using the
protocol implies that all encoders and decoders must support
anything that conforms to that protocol.
Would this make it easier to transform nested JSON into a nested
object/struct? If so it could be useful, very useful.
We’re not sure this is a reasonable requirement. Many formats
do not have any kind of support for arbitrary size integers, for
example. Therefore, we felt it was best to limit it to a set of
concrete types.
I honk we would be missing a trick, unless I am missing something
here, that was very powerful in libraries like Mantle for iOS:
the ability to translate a nested JSON object (some keys in the
JSON object having a JSON object as value, etc...) in an MTLModel
subclass composed of other MTLModel subclasses where doing the
transformation of the root object would call the right model
needed to transform for the child JSON objects.
Working with Mantle is safe, rugged (it does not cause crashes if
the JSON file changes), and allows you to break the problem into
chunks and present a coherent simple view to the code that makes
use of the instance you created out of the JSON input. Reference:
https://github.com/Mantle/Mantle/blob/master/README.md
We could change our minds on this before we ship Swift 4, if we
feel it was the wrong decision. Now that the proposals are
accepted we will be landing these branches in master soon, which
means everyone has a great chance to try it out and see how it
feels in real world usage before it’s final.
- Tony
On Apr 25, 2017, at 3:59 PM, Douglas Gregor via
swift-evolution <[email protected]> wrote:
Proposal Link:
https://github.com/apple/swift-evolution/blob/master/proposals/0166-swift-archival-serialization.md
Hello Swift Community,
The review of SE-0166 “Swift Archival & Serialization” ran
from April 6...12, 2017. The proposal is accepted with some
minor modifications. Specifically, the core protocols and
types will be sunk down into the Swift standard library for
more tight integration with the Swift language and compiler,
and the operations specifically involving Foundation’s
“Data” type will be removed. The proposal document has
been updated with more detail. Thank you everyone for
participating in this review!
- Doug
Review Manager
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