> On Oct 17, 2017, at 10:36 AM, Adam Kemp <adam_k...@apple.com> wrote: > > >> On Oct 17, 2017, at 10:00 AM, Kevin Nattinger <sw...@nattinger.net >> <mailto:sw...@nattinger.net>> wrote: >> >> Once we allow covariant functions to satisfy protocol requirements and have >> generalized existentials and recursive protocol requirements, wouldn't we be >> able to update thusly: >> >> protocol Unordered { >> func map<T>(…) -> Any<U: Unordered where U.Element == T> >> } >> protocol Ordered: Unordered { >> func map<T>(…) -> Any<O: Ordered where O.Element == T> >> } >> > > Now apply that to every order-preserving function that takes a Sequence and > returns another Sequence. You’ve moved the burden from users of API to > implementers of API. It reminds me of the const/non-const split that C++ > developers have to deal with, where a lot of functions end up being > implemented twice so that you can have a const version and a non-const > version (generally one just calls the other). It’s a pain. I don’t want that > when working with Sequences. I don’t think it’s worth it. And FWIW, when I > was programming in C# I wrote functions that took an IEnumerable<T> and > return another IEnumerable<T> very often. It’s a powerful feature that would > have been ruined by a change like this.
The idea is that covariance would mean you only need to implement the function once. > >> As I've been saying all along, elementsEqual returning a functionally random >> result when an unordered type is involved is a problem. > > In theory. Where is the evidence that this leads to a significant number of > real-world bugs? All you’ve done is describe a conceptual problem, but you > haven’t connected the dots to real-world problems. Again, I can point to > .Net, which has a much larger community of developers who have been working > with the same “problem” since version 2.0 released in 2005. If this is a > significant source of bugs then there should be evidence of that. Where is > that evidence? If there are no real-world problems, why do we feel the need to change the function name in the first place?
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