[greenhouse_gas]

Unfortunately, I kind of feel torn: On one hand, I love flutter as a concept[1]. It removes a lot of the baroque from mobile development (no need for the whole RecyclerViewer construction for every list! No Fragments! Doesn't require Android Studio to start working!) but I hate the language (dart). After using Kotlin (let alone Rust), It feels like moving back to Java (no non-nullable types) and in some ways it's actually worse than Java (threads are extremely heavy weight, every interaction with native code is async and slow).

I wish there was:

1. A good Kotlin language server (unlikely, as the company behind the language is an IDE company).

2. A good reactive Kotlin GUI library (meaning, with the ergonomics of Flutter (as in, I don't have to work with Fragments and their lifecycles, just use views)).

3. A good JVM interpreter (to speed up Kotlin/Java compilation)

[1]. No I don't use Flutter to "write two apps for the price of one", as most (of my) apps are just a front-end over a back-end server, so they don't have any special logic worth saving between iOS and Android. I just find Flutter easier to work with relative to Android.

[munificent]

I'm on the Dart team (though I wouldn't necessarily take my comment to be an official statement of the entire team).

> (no non-nullable types)

I really wanted [1] to get those into Dart 1 (way back before Swift and TypeScript even existed), but I couldn't convince language team at the time that it was worthwhile.

When we moved to a stricter, sound type system with strong mode, we hoped to get non-nullable types into that and ship them with Dart 2. But, as you can imagine, migrating millions of lines of code from an optionally typed, unsound type system to a sound, reified static type system is a hell of a lot of work. (I'm not aware of any cases where it's been done at this scale.)

We weren't able to fit non-nullable types into that schedule and into our users' migration pain tolerance. There is only so much you can drag them through, and just getting to strong mode was a lot.

There is still a desire to bring non-nullable types to Dart. It probably won't be soon because we want to give our users a break from migration, and give our implementation teams time to take advantage of the new type system. But I haven't given up on them, and our team's new focus on static ahead-of-time compilation makes them more important than ever.

I agree that Kotlin is a really nice language. I hope we can catch up to them with Dart and exceed them in areas.

[1]: http://journal.stuffwithstuff.com/2011/10/29/a-proposal-for-...

[greenhouse_gas]

The thing is that the longer you wait, the harder it will be to migrate, as the codebase size grows (and once you leave beta, people assume that the language is finalized and won't be too happy being forced to refactor their code when Dart 3 comes out). But as it is, I doubt that the nice parts of Kotlin will ever make it to Dart.

[munificent]

> The thing is that the longer you wait, the harder it will be to migrate.

Definitely preaching to the choir on that one. I pressed my case as hard as I could before 1.0.

We do still have more freedom to make breaking changes than many post 1.0 languages do because, frankly, we don't have that many users. But every day, the cost to make that change goes up.

> people assume that the language is finalized and won't be too happy being forced to refactor their code when Dart 3 comes out

I was worried about that with the transition to the new type system in Dart 2, but users — internal and external — were surprisingly accepting of the breakage. We don't want to be cavalier about breaking them, of course, but my impression is that there is more room for significant changes than I'd initially assumed.

> But as it is, I doubt that the nice parts of Kotlin will ever make it to Dart.

Dart will never be Kotlin, but I hope we can get to a point where most users don't consider it to be deficient compared to Kotlin and where we have some features to make Kotlin users jealous.

[k__]

Yes, it's really sad that a language as young as Dart already has such problems :/

[greenhouse_gas]

It's because the language was made to compile to JS, and competition to JS, so appropriate tradeoffs were made.

For example:

1. JS is single-threaded, with extremely heavy threads only recently made available. So Dart is single threaded, with extremely heavy threads available.

2. JS is weak-typed, so Dart was made optional typed. Remember, it was made before typescript, so they probably didn't expect that such type-heavy features as ADT would interest people.

Kotlin does the same (for example, internal immutability would be much nicer, but since the JVM doesn't support that, neither does Kotlin).

[woolvalley]

From what I've seen how apple did it:

1. They added optional nullability syntax to objective-c, a language that assumes everything is null and doesn't crash when you send a message to nil. If your file uses nullability, it's required for the file, otherwise you don't have to use it. Code without nullability annotations using non-null annotated code could interface with the non-nullable code. Errors didn't come up unless you did very obvious things like directly put nil in a non-null argument.

2. They migrated their entire apple library base to have proper nullability annotations. Code that didn't have nullability annotations continued to work fine. Or I think you could just turn off the build error with a compiler flag.

3. Apple introduced swift. Any objective-c code that didn't have nullability defined was assumed to be an implicitly unwrapped non-null. So if you give a null to something not expecting a nil in swift, it would crash.

Apple has a blog article specifying it further here: https://developer.apple.com/swift/blog/?id=25

-----

I liked this approach for the most part. Migration wasn't that much of a pain, and it was incentivized because I didn't want implictly unwrapped stuff in my swift code.

If you migrated the flutter framework and the dart stdlib to have nullability, then new projects can start with proper nullability annotations from the start, while old projects can progressively migrate files as needed.

Java also has a nullable syntax annotation, and kotlin probably has some sort of java-kotlin nullability interop somewhere. I would really suggest doing it, nullability has given big stability benefits to large projects as it is, and would help adoption in the future as people using something like kotlin & swift for new projects vs flutter itself.

[bsaul]

not sure what's dart like relative to enums, but enum with associated type + optionnals are the absolute killer feature for swift. Steal those and you'll have nothing to worry about.

[LegNeato]

> (I'm not aware of any cases where it's been done at this scale.)

Facebook has done it twice at this scale: PHP -> Hack, plain JS -> Flow JS.

[munificent]

As far as I know, both Hack and Flow are unsound and don't do any runtime type checks to preserve soundness. It's a lot easier to migrate dynamic code to a static type system if you have the luxury of just ignoring the type system when you want to. :)

In Dart 2, the type system is sound and checked at runtime in cases where it can be proven statically safe (downcasts, variance, etc.). That makes it a lot more work to migrate because the code actually needs to run correctly without violating any of the dynamic type tests.

[arxanas]

The Flow core type system is sound: https://dl.acm.org/citation.cfm?doid=3152284.3133872, although there are unfortunately some known unsoundnesses in the actual type system. Does Dart suffer from the same?

Hack does check type hints at runtime, so it's "sound" in the same sense as Java might be. Is this the same sense in which Dart is sound?

> the type system is sound and checked at runtime in cases where it can be proven statically safe

I didn't understand this. If the code is statically proven safe, why would you need runtime checks?

[arxanas]

Neither Hack nor Flow are reified, so it's a different matter.

Both of these languages started out with strict null-checking — Hack because there were too many bizarre falsy values in PHP to allow otherwise, and Flow because it worked out so well in Hack. So neither had to tack on strict null-checking afterwards.

There have been some similar large-scale migration efforts. For example, Hack's record types were built on top of PHP arrays, which don't distinguish between absent and null values. Consequently, Hack's record types didn't distinguish between optional and nullable fields. Furthermore, records support width subtyping by default. This is unsound: you can construct distinct types A and B with A <: B <: A.

After a lot of effort, we did migrate the entire codebase to resolve this unsoundness. Essentially, we changed every record declaration to be an "open" record type and made all new records "closed" by default (referring to whether they supported width subtyping).

The analogue, then, would be something like refactoring every type declaration in every consumer's Dart code to be annotated as nullable, adding explicit null-checks, and allowing them to write non-nullable types as the default thenceforth.

[zerr]

How did you end up in that team, and how one should apply (in case you have any open positions)?

[munificent]

The story of how I ended up on the team is probably too random to be actionable. I believe we do have open headcount, but I don't know how the hiring process works for getting a new hire on to a particular team.

Email me and I'll see what I can figure out.

[kartickv]

Sad to see optional typing go. I thought that's the best of both worlds -- you can write type annotations for documentation or checking, but you also have the benefit of dynamic typing when static typing comes in the way.

[eksemplar]

I have a different view on it, I actually like Dart. I like the strong types and how the language is more suited for enterprise development than both typescript and JavaScript.

There is the added benefit of being able to reuse assets from your mobile app in AngularDart, which I suspect may see an increase in use along with flutter.

I’m not coming from Kotlin or rust though, but a .net core backend with JavaScript on the front end and Xamarin for apps. I can definitely see us move from AngularJS and Xamarin to flutter and AngularDart though as this move would be a nice improvement.

I’m not too worried about the lack of available projects and libraries on dart compared to say JS, as we typically wouldn’t include some one man hobby project anyway.

That being said, I think we’ll wait and see what happens throughout 2018.

[mixedCase]

>is more suited for enterprise development than both typescript and JavaScript.

What makes you think this given the library and tooling situation? Is this strictly a "worse is better" thing where lacking modern language features is a plus (at which point I'd argue for Java) or is there a Dart feature that makes you think it's actually an improvement over TypeScript, Kotlin, .NET Core (both C# and F#) or Rust (just to avoid adding more languages to what you mentioned) for enterprise development?

I'm frankly astonished at seeing how something that I see as an extremely clear step backwards as far as languages go is getting so much traction; not sure if it's just because Flutter is that good a tool (in which case I'd think we should be aiming to make the native core available to other languages) that people are willing to root for the whole package or if there's something else.

[eksemplar]

I think you misunderstood me. I don’t think it’s an improvement over c# (or Kotlin, but I have no experience with Kotlin so I wasn’t commenting on that).

I think it’s an improvement over JavaScript, Typescript and the Xamarin experience + tooling, with the added advantage of letting you share language in your clients.

I don’t think dart is great though, it’s just better than the terrible alternatives.

[frankpf]

TypeScript has ADTs, non-nullable types and the tooling is one of the best (great autocomplete, support for refactorings, incremental compilation, yarn is a great package manager, etc).

Its type system is also one of the most advanced in mainstream languages, being inferior only to Scala and Haskell.

In comparison, Dart doesn't have ADTs or non-nullable types. For a new language, I consider this very underwhelming.

I'm considering using Flutter for a new project because it seems to be a great platform, but having to use Dart instead of TypeScript is a step backwards.

[mixedCase]

>I think it’s an improvement over [...]Typescript

JS I understand, but what makes you prefer Dart over TypeScript in this case?

[korm]

Here are my personal opinions as a long time Dart/JS/TS developer.

- Dart had a lot of features before either JS or TS. Important features like cancellable promises or optional chaining are still missing (I know they might be coming soon). Also some nice quality of life features like named constructors.

- As a superset of JS, Typescript has a lot of idiosyncrasies that might bother people. Personally I don't mind, but people new to web development often find Dart to be a friendlier experience, with fewer pitfalls.

- To me, and this is very subjective, the TS syntax is uglier than either JS or Dart. The types get in the way and add noise to the code. I find Dart's and pretty much any other language's type declarations much cleaner.

However, I have two very big problems with Dart that prevent me from using it as much as I'd like to.

- JS interop is much much cleaner in Typescript/Flow. Every compiled-to-JS language that isn't a superset suffers from this. It's what prevents me from using ReasonML seriously too.

- No support for JSX. I can't go back to writing nested createElement after using JSX

[slifin]

I thought reasonml's JavaScript interoperability was quite good, seems to compile faster and the type system cannot lie about it's inferences like it can in TS

But the main thing for me between TS and reason is exhaustive pattern matching is better in reason, it feels jacky in TS

could I use reasonml/js with flutter widgets and ignore dart?

[k__]

Maybe Dart is simply better than C#/Java but worse than Kotlin?

[georgewfraser]

On (2), there is a Kotlin language server in progress: https://github.com/fwcd/KotlinLanguageServer

[buremba]

A fair comparison would be with JS as all the other alternatives use JS.

[greenhouse_gas]

Or languages that compile to JS (like TypeScript). Maybe one day we'll get languages compiling to Dart[1].

[1]. Although it'll be a pity. JS is stuck as a compilation target because it's a standard, and it's old, and even then wasm may one day take over JS. Flutter could have been a library, and one could have written in Go or Rust or Java with Flutter bindings. As it is now, I don't know if its possible.

[rhodysurf]

Agree the language is the worst part. Honestly if Dart has extensions like Swift and Kotlin, and rust (I think) I would be satisfied though.

[mythz]

Extensions is also my #1 most missed language feature! Wasn't possible before when Dart was dynamically typed, but perhaps now with Dart 2's strong mode we'll see it in future.

[_pmf_]

> It removes a lot of the baroque from mobile development (no need for the whole RecyclerViewer construction for every list! No Fragments!

The Android API sets the bar really, really low for improvements.