[swift-evolution] Smart KeyPaths

[Joe Groff]

> On Mar 29, 2017, at 6:32 PM, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> On Mar 29, 2017, at 6:21 PM, Jonathan Hull via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>>> I would love it if we found a way to retain something as concise as that shorthand.  I'm working on a library where users will specify a collection of key paths pairs.  This shorthand would be a very nice piece of sugar making the code expressing these collections (usually literals) quite a bit more readable.
>> 
>> +1 for this.  I think it will be somewhat common to pass around arrays of these things, and a shorthand syntax of some sort would make that nicer.  That said, I don’t want to slow down the proposal, since I will be using this feature the very second it becomes available.
> 
> Agreed.
> 
> One more thought on this: I don't think anyone really likes the #keyPath(Type, .key1.key2)` syntax; it's just the best we've come up with. If the syntax were instead this:
> 
> 	#keyPath(Type).key1.key2
> 
> I think that would look cleaner and avoid drawing distinctions based on subtle punctuation differences. I don't think it would clash with old-style key paths since you can't have a key path to a type name anyway. And support for the leading-dot syntax would fall out of it quite naturally.

KeyPath objects themselves have properties, so key1 could be a member of KeyPath. This doesn't seem workable. 

-Joe