This is a really important feature IMO, but as others have pointed out it basically amounts to higher-kinded types. I would love to be wrong about this but I am reasonably sure this is out of scope for Swift 4 (otherwise I would be working on a proposal already).
Sent from my iPad > On Mar 11, 2017, at 11:49 PM, Karl Wagner via swift-evolution > <[email protected]> wrote: > > I have a model like this: > > protocol Promise { > associatedtype Result > } > > protocol Scanner { > associatedtype ScanPromise: Promise > > func promiseScan<T>(from: Offset, until: (Offset, Item) -> T?) -> > ScanPromise // where Result == T? > } > > The thing that I’m trying to express is: whichever type implements the > associated type ‘ScanPromise’ must be generic, and that parameter must be its > result (i.e. something it got as a result of calling the “until” closure). > > Even with SE-0142, this kind of constraint would not be possible. What I > would like to write is something like this: > > protocol Promise { > associatedtype Result > } > > protocol Scanner { > associatedtype ScanPromise<T>: Promise // now generic. [SE-0142]: where > Result == T > > func promiseScan<T>(from: Offset, until: (Offset, Item) -> T?) -> > ScanPromise<T> > } > > Thoughts? > > - Karl > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________ swift-evolution mailing list [email protected] https://lists.swift.org/mailman/listinfo/swift-evolution
