[danite]

To me Dart is pretty disappointing. Modern languages like Swift and Rust have shown the power of incorporating functional features like sum types and pattern matching. Dart just feels like the same sort of OO language we've been getting since Java became popular.

Edit: Also the continued existence of null in new programming languages is a baffling choice to me.

[markdog12]

I don't blame you for being underwhelmed. The original goal was an easy to learn language. But since Dart 2.0 was completed, they are working on adding many other language features, including NNBD (Non-null by default).

https://github.com/dart-lang/language/issues

[0x8BADF00D]

It’s just hard to be productive in Dart. The Flutter IDE and simulators were so resource intensive, they literally locked up my laptop the last time I tried using them.

Dart is objectively a terrible language to be productive in for app development. The abstractions provided by the language are clunky to use for window elements on a device screen. Don’t get me started on Material Design, either.

Swift, Objective-C/C++, or even Java is way easier to start building apps with, in comparison. The tooling is mediocre for Dart as well.

[filleduchaos]

I'm not sure what you mean by Flutter IDE and simulators, as the SDK has neither.

[munificent]

Hi, I work on Dart.

> functional features like sum types and pattern matching

"Functional features" means different things to different people. Dart (like most modern languages) has a lot of the core functional features: first-class functions, closures, lambdas, higher-order functions. Our built-in collection libraries are heavily oriented around functional-style transformations. You don't need an external library to map() and filter() your lists to your heart's content.

At the type system level, we also have function types, generic functions, and even first-class generic functions, which is a really unusual, powerful feature.

Sum types are a slightly different beast. Sum types are basically a functional language's answer to subtyping and runtime polymorphism. But object-oriented languages already have full subtyping and polymorphism using classes. There's a sort of zen koan here where algebraic datatypes are a poor man's subclasses and subclasses are a poor man's algebraic datatypes.

The way most multi-paradigm languages like Scala and Kotlin handle this is that sum types are just syntactic sugar for defining a little class hierarchy. Likewise, pattern-matching becomes syntax sugar for instanceof checks and field access. I like that sugar and hope we can add something similar to Dart, but I don't find it's omission to be a profound oversight. It makes some kinds of code nicer, but doesn't significantly affect the expressiveness or capability of the language.

> Dart just feels like the same sort of OO language we've been getting since Java became popular.

Yeah. The original designers of the language designed something very conservative. I think they wanted to make a VM with certain features (single dispatch, static class structure, no static initialization, etc.), and designed the safest language they could come up with to let them do that.

There is a lot of benefit to familiarity. I like classes and C-family syntax, and we see very clearly that Dart is really easy for people to learn and become productive in. We've done user studies where participants have been able to write correct Dart code without knowing what language they were using. It's hard to underestimate the value of that.

But there is also value in providing the modern tools people want in order to write clean, beautiful, correct, maintainable code. Dart has some catching up to do there. We're making a lot of progress. With Dart 2.0, we replaced the old unsound optional type system with a real, modern, expressive, sound static type system. It was a ton of work to do that while dealing with millions of lines of existing code.

We didn't get all the type system features we wanted, but we have a foundation we can build on now. The optional type system had some nice properties, but was effectively a dead end. When your types are optional, you can't hang any language semantics off them. That takes lots of features off the table: implicit conversions, extension methods, etc.

> Also the continued existence of null in new programming languages is a baffling choice to me.

I have always believed [0] that not having non-nullable types was a mistake in Dart 1.0. We are fixing it now:

https://github.com/dart-lang/language/blob/master/working/01...

There's a lot of work to do, but I'm really excited with the design. Unlike many other languages, we have something that becomes fully sound with respect to null errors. This means that once a program is fully migrated, a compiler will be able to take advantage of non-nullable types for performance optimizations. It will be quite a while before we get to the point where we can do this, but it's cool that that's on the table.

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

[mixedCase]

> It makes some kinds of code nicer, but doesn't significantly affect the expressiveness or capability of the language.

Sum types and exhaustive pattern matching aren't about expressiveness, they're tools for aiding code comprehension by increasing the locality of code that has no business being distributed into completely different classes, and decreasing the cost of making changes by heavily reducing the amount of test code that needs to be written to make sure a closed set of options is handled appropiately; in OOP languages you can get this by using interfaces but to make use of it you'd have to use huge classes with methods pertaining to every usage of this closed set.

I would never willingly pick up another language that doesn't provide me with them after experiencing the productivity gains. I really like the direction Dart is moving towards and the steps taken demonstrate there's a team behind it that cares about correctness and productivity over being just a familiar Java-like, but this is the one hard blocker for me.

[munificent]

> they're tools for aiding code comprehension by increasing the locality of code that has no business being distributed into completely different classes

That's true for some kinds of code but not others. This is the classic Expression Problem [0]. For some things, it makes sense to keep all of the code for a single operation together. For others, it makes more sense to keep all of the code for a single datatype together. ML-style languages optimize for the former, and object-oriented languages optimize for the latter.

In practice, for the kinds of code Dart is designed for, the latter is a better fit most of the time. There's a reason OO and UI have been married together for decades.

Ideally, a language provides both styles so you can choose the one that fits your problem best. You see that now with languages like Scala. I hope we get there with Dart too.

I don't think it's fair to say that subclassing and method dispatch is objectively wrong just because it's a bad fit for some kinds of code. (Though, naturally, if it's a bad fit for the kind of code you need to write, then an OO language might be an objectively bad choice for you.) Class-based method dispatch is annoying for some things (God knows I've written enough Visitor pattern implementations over object-oriented AST class hierarchies), but it's really beautiful for others.

Being able to define a new widget class that bundles its rendering and interaction behavior together and can seamlessly extend a UI framework is something so natural that we take it for granted, but is very difficult to express in a language like SML. In fact, in order to do it, you'll probably end up doing a "design pattern" that reimplements something like v-tables at the application level.

[0]: http://journal.stuffwithstuff.com/2010/10/01/solving-the-exp...

[mixedCase]

Not sure if I gave off the wrong impression, but I am not a proponent of having only sum types and discarding hierarchies; as you well mentioned each is well-suited to specific usecases.

I do however disagree on subclassing being the best fit for UI code. "The Elm architecture" as well as the model presented by React functional components with hooks offer sets of tradeoffs that I at least have found are better for most of the development I find myself doing when writing (and particularly when maintaining) regular business frontends.

[xkapastel]

> There's a reason OO and UI have been married together for decades.

People repeat this a lot, that OO goes with UI, but I don't think it's actually true, and I think e.g. React Hooks and immediate mode GUI in general demonstrate that it's not true. OO has been coupled with UI out of inertia, not because OO has unique strengths when applied to UI.

Sum types are a primitive language feature, akin to product types, which absolutely no one rejects the value of. The sum/product analogy to arithmetic is compelling to me: they are the building blocks of complex types and deserve recognition. I think that "zen koan" you mentioned earlier is being very generous to subclassing. You want ADTs most of the time!

[munificent]

> People repeat this a lot, that OO goes with UI, but I don't think it's actually true

It is evidentially true. Thousands of successful applications and a billions of lines of UI code have been written in object oriented languages. It does work and it can't be that bad if that's continuing to happen even after the emergence of other alternatives.

Whether there are better ways is a good question, but I think it's pretty clear that you can ship good apps using OOP for your UI.

> React Hooks and immediate mode GUI in general demonstrate that it's not true.

I'm far enough into my career now — I've been doing UI programming of one form or another since the 90s — to have seen that pendulum swing several times. If there is a silver bullet, we haven't found it. It's probably not immediate mode GUIs because if it was, I wouldn't have seen game teams tear them out to replace them with something more retained several times in the 2000s.

What I think actually happens is that we forget the problems lurking in the solution we are not currently using. The grass over there gets greener and greener until we hop the fence and the cycle starts over. Incremental progress does happen. (I am not keen to revisit MFC any time soon.) But if a given concept (1) has been around a long time (2) has not already supplanted the alternatives, it's pretty unlikely that it is now an amazing solution today. The only time when that isn't true is when the surrounding technology context has changed since then.

For example, neural nets weren't a good solution for AI problems in the 80s because compute was too expensive and we didn't have a lot of data. Now that CPUs are cheap and everyone puts their entire life on the Internet, machine learning is here.

I haven't seen anything around UIs that to me looks like a significantly changed context, so I think we're still orbiting around retained-mode and immediate-mode as both having their own trade-offs and neither being a slam dunk.

> I think that "zen koan" you mentioned earlier is being very generous to subclassing. You want ADTs most of the time!

I really don't think that's true. Just look out there in the world. More code is written in languages doing subclassing every day than in languages with sum types. Despite the fact that sum types have been around since the 70s. You have to have a very uncharitable opinion of all of your fellow programmers to believe they've all been getting this wrong for decades. Heck, the software you are using right now to read this comment is sitting on a stack of several layers of subclass-based architectures! You've got JS running on top of the DOM inside a browser written in C++.

Sum types are really nice. But open-ended subclassing is too.

[malkia]

I wanna hear more open discussion about immediate & retained mode approach.

For one imgui gains traction again, especially among game developers, simply as it gives a lot for the ease of compile, understanding, compactness of code, etc. You can really build complex tools out of it.

But there is one nasty elephnant - the state, and imgui's approach is to hide it somehow - it used be behind your __LINE__ (or __COUNTER__, stack.line in some langs), or maybe part of your label points to your data, and if you've had the bad luck of having same labeled names, then there is yet another workaround, something special hidden in there.

All in all, it seems like it's missing a language feature, and we are suddenly grasping on all kinds of tweaks to achieve that.

That, .. and layout.. Layout is damn hard in immediate language. It works by magic, and then your app might crash, and lock. No I'm not kiddin...

Then again I'm but a simple user of UI toolkits, never fully written one.

[xkapastel]

First, I just want to say that I use Dart pretty regularly now and enjoy the language. I don't want to come across as overly negative; Dart is a solid language that's made web programming a lot more fun for me. So thank you, and everyone else on the Dart team for the hard work!

I just want to address these lines:

> Thousands of successful applications and a billions of lines of UI code have been written in object oriented languages.

> More code is written in languages doing subclassing every day than in languages with sum types. Despite the fact that sum types have been around since the 70s. You have to have a very uncharitable opinion of all of your fellow programmers to believe they've all been getting this wrong for decades.

I agree that there's a huge amount of code out there using subclassing and not sum types. I'm not disputing the utility of subclassing; I just think the analogy to arithmetic is compelling, in that a closed sum type is a more primitive notion than open ended subclassing. It's easier to describe what a sum type is than what a subclass is; sum types have a smaller impact on a type system than subclassing. Pretty much any metric you can think of, sum types are just simpler, and more widely applicable. Any time you are describing a data structure, an ADT is immediately useful; subtyping may or may not be useful and is always more complicated. It's very difficult for me to understand how anyone could possibly say subtyping is on the same level as a basic operation like addition. Subclassing may or may not be nice but sum types are a primitive in a way that subclassing simply cannot be.

I don't know how to break it down more than this: we already have multiplication of types, and everyone accepts this as a primitive. Well, you can also do addition of types! Multiplication, addition, a neat little pair, just like algebra class[0]. Subclassing is way more complicated than this. That's it, that's a bullet proof argument as far as I'm concerned.

I suppose I do have an uncharitable opinion of mainstream programming languages, because I do think they've been getting this wrong for decades. It's nothing personal, it's just that industry has other concerns besides how clean their languages are. My browser being written in C++ is not an argument in favor of subclassing, though. You can build anything out of toothpicks if you're paid enough.

[0]: https://typedefs.com/introduction/

[kitsunesoba]

Indeed, Flutter would be much more compelling if I could use it with Rust or Swift instead. Dart really doesn’t interest me.

[IshKebab]

One nice think about Dart I've found is that compile times are very fast (faster than Go) and when editing in VSCode the code intelligence is instant and 100% accurate in my experience.

Compare that to Rust where compilation speed is almost as bad as C++, RLS is slower than e.g. Qt Creator's clang lints, and has auto-completions so innaccurate that they are almost worse than nothing.

Buuut.... I wanted to make a deep copy of an object (a map of maps) in Dart, and one of the suggestions on Stackoverflow is to serialise it to JSON and then deserialise it. Eek. In C++ you just do `auto a = b;`. In Rust `let a = b.clone();`. How do they leave out such basic functionality?

https://stackoverflow.com/a/26616081/265521

[munificent]

> In C++ you just do `auto a = b;`.

Sure, but does it do what you want? :) If that map contains pointers or other types with "interesting" assignment semantics, then your idea of a deep copy and that author of that type's idea may not be the same. Cloning is a surprisingly hard problem.

The two languages you compare to don't have GCs and prefer value semantics. But in most GC languages, everything is by reference and "copying the bits" isn't as meaningful of an operation.

I looked up how to deep clone maps in some other GC languages:

https://stackoverflow.com/questions/4157399/how-do-i-copy-a-...

Ruby: Top suggestion is to marhsall/unmarshall it.

https://stackoverflow.com/questions/5105517/deep-copy-of-a-d...

Python: Import a separate "copy" module. May have to implement some custom methods if you use user-defined objects in the map. The module isn't thread-safe. A comment recommends converting to JSON and back.

https://stackoverflow.com/questions/28288546/how-to-copy-has...

Java: No built in solution. Have to traverse the map yourself and do element-wise copies.

[scalatronn]

As someone who uses dart everyday - it's quite nice language. All I'm missing is case / data classes, non-nullable types and pattern matching, but they're changing the language and all of those will eventually come. For now, I will use built_value and built_collections ;)

[IshKebab]

> your idea of a deep copy and that author of that type's idea may not be the same

Definitely true that they may have done something weird, but I think the idea of a deep copy is pretty easy to define: It should not be possible to modify the original object using only the deep copy. (Note that this doesn't preclude copy-on-write, etc.)

I think it is quite weird that so few languages (even GC'd ones) provide a proper solution for this. It's clearly a thing people want to do.

[pjmlp]

Surely not faster than Delphi, oh well.

[Kiro]

What's wrong with null?

[coldtea]

A null is not a string or an integer or a MyClass instance, etc. So why does it pollute variables of all those types?

https://medium.com/@hinchman_amanda/null-pointer-references-...

https://www.infoq.com/presentations/Null-References-The-Bill...

https://www.quora.com/Why-was-the-Null-Pointer-Exception-in-...

https://www.lucidchart.com/techblog/2015/08/31/the-worst-mis...

[Kiro]

Thanks. Stupid question but consider the following:

  entity = Entity.fetch(id)
  if (!entity) doSomething()

Entity.fetch returns null if it doesn't find anything. How would this work without null?

[ptx]

You would still have null, but only when asked for and checked explicitly.

In Kotlin, for example, you mark something with a question mark to say that it can be null, which forces you to check for null before using it:

  val entityOrPossiblyNull: Entity? = Entity.fetch(id)

  if (entityOrPossiblyNull == null) {
      doSomething()
  }
  else {
      // The compiler knows that the variable is not null in this branch,
      // so this assignment is OK.
      val entityForSure: Entity = entityOrPossiblyNull

      doSomethingWithEntity(entityForSure)
  }

[wtetzner]

The real problem isn't null itself, it's that in most languages that have it, null inhabits all types (or at least all reference types).

Different languages solve this problem in different ways. Many languages get rid of null entirely, and use option types in its place. Other languages, like Kotlin, fix it in the type system, by differentiating between e.g. String and nullable String (spelled String? in Kotlin) .

[coldtea]

There are several ways. A popular one is an Optional type. Here's how Java does it: https://www.baeldung.com/java-optional