Can AnyKeyPath be extended to provide a path String?

DevAndArtist · March 13, 2019, 5:07pm

I wonder if it would be possible to extend AnyKeyPath with a property that returns key-path as a string. Right now there is this hidden hook but it is not guaranteed to return the path at all as the return type is optional:

github.com

apple/swift/blob/main/stdlib/public/core/KeyPath.swift#L122


      
                    return false
                  }
                  if aType == nil {
                    return true
                  }
                }
              }
            }
          }
          
          
// SPI for the Foundation overlay to allow interop with KVC keypath-based
          // APIs.
          public var _kvcKeyPathString: String? {
            @_semantics("keypath.kvcKeyPathString")
            get {
              guard let ptr = _kvcKeyPathStringPtr else { return nil }
          
          
    return String(validatingUTF8: ptr)
            }
          }

It also has has a different representation than the actual key-path might look in code.

For example the following two key-paths from a UIViewController:

\.view.isOpaque
\.view.isHidden

Will produce the values Optional("view.opaque") and Optional("view.hidden"). However I would wish for a simple property like var keyPathString: StaticString/String { get } that returns "view.isOpaque" and "view.isHidden".

beccadax · March 13, 2019, 5:12pm

What do you want to do with the string?

fclout · March 13, 2019, 5:13pm

My understanding is that it is a conscious design decision to not include these strings, as it can reveal details about the inner workings of your program, which is a downside of Objective-C for several users.

DevAndArtist · March 13, 2019, 5:17pm

I would like to hash a custom type, keyed by a string, created using a key-path by also avoiding collisions.

Right now I'm abusing hashValue as it's the only value that provides some sort of uniqueness.
I'm doing something like this "\(Root.self).\(keyPath).\(keypath.hashValue)". (Edit) I worked around this problem actually, but the main question remains.

Can/should we extend AnyKeyPath with such property in the future?

jrose · March 13, 2019, 5:38pm

Key paths are already unique (and Hashable) themselves.

Not every key path has a string representation; only those that represent Objective-C properties. So this isn't doable in the general case (unless we start putting a lot more metadata into binaries).