[swift-evolution] [Review #2] SE-0161: Smart KeyPaths: Better Key-Value Coding for Swift

[Douglas Gregor]

> On Apr 6, 2017, at 1:15 PM, Michael J LeHew Jr <lehewjr at apple.com> wrote:
> 
> 
>> On Apr 6, 2017, at 10:37 AM, Douglas Gregor via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> 
>>> On Apr 6, 2017, at 10:28 AM, Ricardo Parada <rparada at mac.com <mailto:rparada at mac.com>> wrote:
>>> 
>>> Do you think in the future it might be possible to convert to strings?  
>>> 
>>> For example, I am imagining a CoreData-like framework on the server (where there is no Objective-C), where I would like to get the type of the root object and keys forming the path.  That way I can go to an object model, get the corresponding entity, and traversed relationships, and destination attribute.  All that information (table name, table joins for the relationships traversed, column names, etc.) would then be used to construct the SQL.
>> 
>> Key-paths could be extended to allow introspection of the components along the path, in which case you would be able to map between key paths into your specific data model and the tables/columns in your database. This is not the 
> 
> ... ?  You left us hanging there Doug! :)

Eh, sorry! Making key-paths Codable could definitely make sense in the future, as you note. But I don’t know that a “blessed String representation” makes sense for key-paths.

> 
> We do mention in the proposal that support for marshalling to external representation (String, Codable should that be accepted, etc) would highly desirable in the future, for IB / CoreData type scenarios and more.  It is one of the principle reasons we decided not to allow key paths to compose with transformations (functions and closures), as while that is very powerful and interesting, once you go there you're not really a key path any more. 
> 
> It's not part of this initial proposal, but could easily be brought up as a follow-on in the future. 

Right.

	- Doug

> 
>> 
>> 	- Doug
>> 
>>> 
>>> 
>>> 
>>>> On Apr 6, 2017, at 12:37 PM, Douglas Gregor <dgregor at apple.com <mailto:dgregor at apple.com>> wrote:
>>>> 
>>>>> 
>>>>> On Apr 6, 2017, at 9:31 AM, Sean Heber <sean at fifthace.com <mailto:sean at fifthace.com>> wrote:
>>>>> 
>>>>> 
>>>>>> On Apr 6, 2017, at 11:19 AM, Douglas Gregor <dgregor at apple.com <mailto:dgregor at apple.com>> wrote:
>>>>>> 
>>>>>>> 
>>>>>>> On Apr 6, 2017, at 8:13 AM, Ricardo Parada via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>>>> 
>>>>>>> I agree, there's an analogy between strings and key paths, and in that regards the single quote would make sense.  I would not complain.  
>>>>>> 
>>>>>> The only analogy between strings and key-paths is that the existing Cocoa APIs for key-paths use strings. That’s not an analogy to hang language syntax on, because it’s relevance will fade quickly. 
>>>>> 
>>>>> Why would it fade quickly? Do we expect the concept of keypaths to go away over time? If so, why are we even designing a syntax for keypaths?
>>>> 
>>>> The link between key-paths and strings will go away over time. The *only* reason anyone associates strings with keypaths is because Cocoa’s current key-paths are string-based. This proposal makes any string representation of key-paths an implementation detail that could be used for interoperability with Cocoa’s current system. There is no reason for a type-unsafe string representation to ever be in the user model.
>>>> 
>>>> 
>>>>>> The core team discussed single quotes, and decided that we want to save them for something in the string/character realm.
>>>>> 
>>>>> Are they to be saved for something specific or is this just because a lot of languages use single quotes for character literals? Why is this association any more sacred than an association with Cocoa string keypaths?
>>>> 
>>>> 
>>>> Lots of languages use single quotes for character literals; we may want to bring them back for it.
>>>> 
>>>> 	- Doug
>>> 
>> 
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