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

[Matthew Johnson]

> On Mar 16, 2017, at 4:18 PM, Philippe Hausler <phausler at apple.com> wrote:
> 
> One point of concern with making the implementations rely on that: it would require any adopter of Codable to be built in swift 4 mode no? it might be valuable to keep the protocol not requiring Swift 4 to aide in incremental migration.

Yes, probably so.  I would be disappointed if we allowed the design of Swift 4 features to be influenced by Swift 3.1 compatibility.

> 
>> On Mar 16, 2017, at 2:14 PM, Matthew Johnson via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> 
>>> On Mar 16, 2017, at 4:12 PM, Itai Ferber <iferber at apple.com <mailto:iferber at apple.com>> wrote:
>>> 
>>> If throwing subscripts made it in the Swift 4 timeframe, then we would certainly consider it.
>>> 
>> Cool.  Any comment from the core team on whether this is a possibility?  If it is and nobody else wants to write a proposal I would be willing to do it.
>>> On 16 Mar 2017, at 13:19, Matthew Johnson wrote:
>>> 
>>> 
>>>> On Mar 16, 2017, at 3:01 PM, Itai Ferber <iferber at apple.com <mailto:iferber at apple.com>> wrote:
>>>> 
>>>> Subscripts, by the way, would not help here, since they cannot throw. decode must be able to throw.
>>>> SR-238 <https://bugs.swift.org/browse/SR-238?jql=text%20%7E%20%22subscript%20throw%22>; for Apple folks, 28775436.
>>>> 
>>> They don’t “help” but they do provide a more natural interface.  If the Foundation team feels a more wordy interface is necessary that is ok.
>>> 
>>> I specifically mentioned that they can’t throw yet.  Throwing subscripts would make a good companion proposal if they could fit into the Swift 4 timeframe.  If not, then yes we need a method rather than a subscript.  But if we can get throwing subscripts into Swift 4, why not use Swift’s first class syntactic support for keyed access to keyed containers?
>>> 
>>>> On 16 Mar 2017, at 11:46, Matthew Johnson via swift-evolution wrote:
>>>> 
>>>> 
>>>> 
>>>>> On Mar 16, 2017, at 1:34 PM, Zach Waldowski via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> 
>>>>> On Thu, Mar 16, 2017, at 02:23 PM, Matthew Johnson via swift-evolution wrote:
>>>>>> I don’t have an example but I don’t see a problem either.  There are two options for specifying the return type manually.  We can use the signature you used above and use `as` to specify the expected type:
>>>>>> 
>>>>>> let i = decode(.myKey) as Int
>>>>> 
>>>>> The awkwardness of this syntax is exactly what I'm referring to. Would a beginner know to use "as Int" or ": Int"? Why would they? The "prettiness" of the simple case doesn't make up for how difficult it is to understand and fix its failure cases.
>>>>> 
>>>>> Any official Swift or Foundation API shouldn't, or shouldn't need to, make use of "tricky" syntax.
>>>> 
>>>> I don’t think this is especially tricky.  Nevertheless, we can avoid requiring this syntax by moving the type argument to the end and providing a default.  But I think return type inference is worth supporting.  It has become widely adopted by the community already in this use case.
>>>> 
>>>>> 
>>>>>> If we don’t support this in Foundation we will continue to see 3rd party libraries that do this.
>>>>> 
>>>>> The proposal's been out for less than 24 hours, is it really productive to already be taking our ball and go home over such a minor thing?
>>>> 
>>>> I don’t think that’s what I’m doing at all.  This is a fantastic proposal.  I’m still working through it and writing up my more detailed thoughts.
>>>> 
>>>> That said, as with many (most?) first drafts, there is room for improvement.  I think it’s worth pointing out the syntax that many of us would like to use for decoding and at least considering including it in the proposal.  If the answer is that it’s trivial for those who want to use subscripts to write the wrappers for return type inference and / or subscripts themselves that’s ok.  But it’s a fair topic for discussion and should at least be addressed as an alternative that was rejected for a specific reason.
>>>> 
>>>>> 
>>>>> Zach Waldowski
>>>>> zach at waldowski.me <mailto:zach at waldowski.me>
>>>>> 
>>>>> 
>>>>> 
>>>>> 
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