KEEP VS swift-evolution

Most other languages agree that checked exceptions are not good by not having them.

As for alternatives, Try/Result and similar monads have decent adoption even in Java, but personally I quite like the Kotlin philosophy [1] to not have generic error containers and either use runtime exceptions or make failures of the return type.

[1] https://github.com/Kotlin/KEEP/blob/master/proposals/stdlib/...

The nitty-gritty is in the KEEP. They show in the end how they considered to add type classes, and then discarded the idea.

Lenses work today. And I think the value class feature will be awesome.

https://github.com/Kotlin/KEEP/blob/master/notes/value-class...

Seems like Kotlin Context Receivers then (https://github.com/Kotlin/KEEP/blob/master/proposals/context-receivers.md).

Kotlin has value classes. Here's a good overview of how they work in Kotlin: https://github.com/Kotlin/KEEP/blob/master/notes/value-class...

That document is a few years old now and was intended as a design document. But Value classes shipped with Kotlin 1.5. Apparently they are compatible with the project Valhalla value objects that will be added to the JVM at some point. So, this stuff is coming.

I had to look it up because even though I write Kotlin a lot, value classes are not something I have used at all. Looks useful but not that big of a deal and doesn't really solve a problem I have. Data classes and records (in Java) are a bigger deal IMHO.

In practice, the way you deal with immutability in Kotlin is to keep most of your data structures immutable by default unless they need to be mutable. E.g. there's a List and a MutableList interface. Most lists are immutable unless you create a MutableList. Same with val vs. var variables. Val variables can't be reassigned and you kind of use var only by exception when you really have to. The compiler will actually warn you if you do it without good reason. A data class with only vals can't be modified. Java is a bit more sloppy when it comes to mutability semantics. It has records now but all the fields have setters by default. It has var but no val assignments (you can use final to force this but few people do). And so on.

Semantically this is not as strong as what Rust does of course but it's good enough to make e.g. concurrency a lot easier. Mostly, if you avoid having a lot of mutable shared state, that becomes a lot easier.

You could imagine a Kotlin like language with much stronger semantics implementing borrow checking instead of garbage collection. It wouldn't be the same language of course but I don't think it needs to be very different. Using it would not be a massively different.

I'd be very interested in a comparison between scala 3 using/given and Kotlin new context receivers https://github.com/Kotlin/KEEP/blob/master/proposals/context...

This will be furthermore simplified with multiple receivers coming very soon

Tfw no pattern matching. :(

No, it's not. Refcounting CAN be a garbage collection algorithm, but in Swift it's deterministic and done at compile time. Not to mention recently added support for non-copyable types that enforces unique ownership: https://github.com/apple/swift-evolution/blob/main/proposals...

> It's super easy to cause its type check to timeout, which is something I haven't seen when using Rust.

Yeah, the operator overloading design makes it too easy to construct an exponential search space.

> For instance, Swift doesn't have the orphan rule, so it's possible that 2 packages implement the same protocol for the same type, and when this happens currently there are no solutions;

There's now a warning about this: https://github.com/apple/swift-evolution/blob/main/proposals.... What other solutions can there be other than making it a hard error? It seems like an inherent drawback of typeclasses over first-class modules.

> there is this strange design decision that classes and structs should be different things and each have their own set of random limitations

structs in Swift are the same as structs in Rust, and a class is a heap-allocated reference counted box, like an Arc>.

> and there is SwiftUI, which hacks on the syntax itself, making statements no longer mean what they are supposed to mean

Result builders are a language feature and not part of SwiftUI: https://github.com/apple/swift-evolution/blob/main/proposals...

Just last week owning and borrowing parameters got accepted as well. https://github.com/apple/swift-evolution/blob/main/proposals...

It’s been the focus for a while especially after the concurrency work. It’s probably the final major feature before Swift 6

Swift 5.9 dropped at WWDC, and with it came with noncopyable value types:

https://github.com/apple/swift-evolution/blob/main/proposals...

as well as a way to explicitly move types:

https://github.com/apple/swift-evolution/blob/main/proposals...

I haven’t read either in-depth, though!

They actually can figure that out, though [0]. I hope this can solve some of it because their deployment model is the dumbest fucking thing. I'm glad they figured out how to backport async/await, it's just impossible to use in a serious library otherwise.

[0] https://github.com/apple/swift-evolution/blob/main/proposals...

https://www.swift.org/swift-evolution/ is where the discussion and planning of the evolution of Swift takes place.

Sure, here’s the most recent Swift Evolution proposal as an example: https://github.com/apple/swift-evolution/blob/main/proposals/0395-observability.md

There’s a pretty good write up by Chris Lattner from when they originally removed it, and I tend to agree with his explanation.

This is an opaque result type as introduced by SE-0244 and is available in Swift 5.1 with Xcode 11. This behaves like a “reverse generic”. In a traditional generic function, caller decides what types get bounded to callee’s generic arguments. But with opaque result type, the return type is chosen by the callee and comes back to the caller as abstracted.