[swift-evolution] Smart KeyPaths

[Matthew Johnson]

> On Mar 22, 2017, at 11:16 AM, Ricardo Parada <rparada at mac.com> wrote:
> 
> I see three possibilities:
> 
> 1) # + «space» +«path» like this:
> 
> let path = # Bag.things[0].name
> bag[path] 
> bag[# Bag.things[0].name]
> bag[# .things[0].name]  // Root is inferred as Bag
> bag.things[0][# Thing.name]
> bag.things[0][# .name] // Root is inferred as Thing
> 
> 2) # + «path» like this::
> 
> let path = #Bag.things[0].name
> bag[path] 
> bag[#Bag.things[0].name]
> bag[# .things[0].name]  // Root is inferred as Bag
> bag.things[0][#Thing.name]
> bag.things[0][#.name]  // Root is inferred as Thing
> 
> 3) «Root» + # + «path» like this: 
> 
> let path = Bag#things[0].name
> bag[path] 
> bag[Bag#things[0].name]
> bag[#things[0].name]
> bag.things[0][#name]
> bag.things[0][Thing#name]

I prefer the third option.  I don’t think we should go with the first option.  Allowing (or requiring) a space seems likely to be confusing.  Both the first and the second still have potential to be confusing.  If `Bag` has a static property named `things` people could be confused about what `#Bag.things` refers to.  If we’re going to use a special sigil it should be positioned such that it eliminates potential for that kind of confusion.

> 
> 
> 
>> On Mar 22, 2017, at 11:47 AM, Matthew Johnson <matthew at anandabits.com <mailto:matthew at anandabits.com>> wrote:
>> 
>> 
>>> On Mar 22, 2017, at 10:36 AM, Vladimir.S via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> On 22.03.2017 17:37, Ricardo Parada wrote:
>>>> 
>>>> 
>>>>> On Mar 22, 2017, at 9:30 AM, Vladimir.S <svabox at gmail.com <mailto:svabox at gmail.com>> wrote:
>>>>> 
>>>>> let path = @Bag.things[0].name
>>>>> 
>>>>> bag at path
>>>>> bag at .things[0].name
>>>>> bag at Bag.things <mailto:bag at Bag.things>[0].name
>>>>> bag.things[0]@.name
>>>>> bag.things[0]@Thing.name
>>>> 
>>>> It sounds like the @ character is serving two different purposes which confused me at first.
>>>> 
>>>> If I understood correctly, you are using it to get the key path but also to apply the key path to the bag struct and get the corresponding value.
>>>> 
>>> 
>>> Yes. And the initial proposal suggest the following syntax accordingly:
>>> 
>>> let path = Bag.things[0].name
>>> bag[path]
>>> bag[.things[0].name]
>>> bag[Bag.things[0].name]
>>> bag.things[0][.name]
>>> bag.things[0][Thing.name]
>> 
>> # makes a lot more sense than @ as a sigil.  It follows from #selector and #keyPath.  These are the most similar language features right now where the compiler produces special values.  I think it’s also worth noticing that values produced by #selector and #keyPath are used in normal ways.  There is no magic syntax for their use, just a typed value.  If we’re going to make a change we should use # instead of `.` for accessing these special values but we should stick with subscript for use.
>> 
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>> 
> 

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