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Comment by DCKing | Hacker News Reader

> Is not about type safe, Dart can be used as both, a type safe lenguage and as a dynamic lenguage, demanding to cover a certain part of of what a type safe language has it is reasonable, now, if the package was to big for Dart designers they should have made Dart a dynamic language only.

If the goal is not to make it type safe, then there is really no objection to just use the built-in Map+List JSON parser, is there?

> I see this as a way to mitigate the desing problems Dart it self has.

How could a language a language possess both classes and not spend a lot of complexity trying to shoehorn JSON objects to fill the data in those classes? This is not a problem of Dart, this is a problem of class-based object orientation. It baffles me that people expect it to arbitrarily map JSON to those classes when the associated complexity is well-known.

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> It baffles me that people expect it to arbitrarily map JSON to those classes when the associated complexity is well-known

That's because you're adding complexity that nobody is asking for. Deserialising JSON onto a simple PODO with no inheritance, no mis-matching of properrty names, etc., is a pretty trivial requirement. The impelementation complexity is being used as an excuse not to meet a really basic need of a web app.

Please tell me - how am I supposed to get data from a server, into a data structure that will give me code-completion and type checking? Other languages with types do this fine; why should I hand-code a load of mapping of basic values in Dart?

> Please tell me - how am I supposed to get data from a server, into a data structure that will give me code-completion and type checking?

Write a fromMap constructor.

> Other languages with types do this fine; why should I hand-code a load of mapping of basic values in Dart?

For one thing, to reduce the degree of coupling between your client code and the interchange format. With a fromMap constructor, anything interchange format that can deserialize into a generic map-of-strings-and-lists-of-strings format can be used (and different external JS structures can be supported, as well, with a simple Map-to-Map converter.)

Automagic mapping that relies on matching field names between objects and interchange formats results in tight coupling between client and interchange format.

> Deserialising JSON onto a simple PODO with no inheritance, no mis-matching of properrty names, etc., is a pretty trivial requirement.

This is not serializing into a PODO. This is serializing into a simple struct. Dart does not have simple structs, so you get no deserialization of simple structs.

Imagine that you write a core library function that does what you want. It cannot map arbitrary classes, but only a subset of classes that adheres to a "simple structure". The developers would then have to tell you which classes you can use it on, and which classes you can't. It would give you runtime errors when you happen to include inheritance somewhere in your project. It's an unmaintainable situation, and most safety of static checking would be gone. Not just in your project, but every project using that feature. Think of the developers' perspective. Why would they want to include such a fragile feature in the first place?

You could argue that Dart needs a "struct"-like construct just to support deserialization. Still the problems remain that that still has all the fragility problems of reflection. Good luck with convincing the developers about adding a language feature for that. They have already shown to not be receptive to that idea [1][2].

You are free to hack your way around typesafety, but you cannot make this a problem of the developers. A type safe language simply brings you inconvenience when you're trying to shoehorn dynamic data in static structure definitions. This is not the Dart developers' problem: increased type safety is their goal.

> Please tell me - how am I supposed to get data from a server into a data structure that will give me code-completion and type checking?

You either write your own code to do this or don't do this at all and just use the data in another shape. You can keep repeating this point all day long; you won't demonstrate why it is anything more than "nice to have", let alone that it's a "necessity".

> Other languages with types do this fine.

AFAIK only .NET-based languages and Go do this out of the box. Both can include this out-of-the-box because they are server oriented languages and can include all the complexity they want. Those languages don't care for the binary size of their applications as much as Dart applications.

[1]: https://groups.google.com/a/dartlang.org/forum/#!topic/misc/...

[2]: https://code.google.com/p/dart/issues/detail?id=10374

>If the goal is not to make it type safe, then there is really no objection to just use the built-in Map+List JSON parser, is there?

A Map is not type safe, at least, not the default result of a JSON.decode in Dart, actually, the result is a dynamic Map. I don't know what your point is.

>This is not a problem of Dart, this is a problem of class-based object orientation

It is not a problem, it is a must have. The associated "complexity" was overcome many years ago with Generics (or templates), Dart has this, so, there is no excuse.

> A Map is not type safe, at least, not the default result of a JSON.decode in Dart, actually, the result is a dynamic Map. I don't know what your point is.

A dynamic type does not give you type safety, and neither does a dynamic Map. A dynamic type might give you a little more type safety than a map, but invalid member access would give you as much headache in both situations. So why even bother dragging in so much complexity for this when you can just write your own code?

> It is not a problem, it is a must have.

You say that as if it's a fact. Have I not put enough on the table to demonstrate that what you're saying is 1) an opinion 2) a minority opinion 3) is ignorant of the associated complexities 4) demonstrably not necessary for web applications?

> The associated "complexity" was overcome many years ago with Generics (or templates), Dart has this, so, there is no excuse.

Please explain how generics helps in overcoming this complexity. I'm genuinely interested.

Please before I can answer you, tell me what is that mythical "complexity" in doing it first, because, we haven't stablished what is it, what is actually the problem?

>is ignorant of the associated complexities

Tell me what complexities?

Look at how much code Jackson uses for their core serialization: https://github.com/FasterXML/jackson-core . This is a (the?) .NET library for the same: https://github.com/JamesNK/Newtonsoft.Json/tree/master/Src/N...

That's a lot of code, don't you think? Quite a bit of work to write it. Quite a bit of edge cases to cover. It's fine to include this in your compiled distributed server or client application. But it's quite a problem if it needs to be loaded in the browser. You could argue that a simpler, less complete implementation is in order. But what language developer would want to include an API that is known to be incomplete and therefore fragile? This seems to be a job for an external library.

I'm still trying to find another statically typed class based compile-to-JS language that does deserialization like proposed, but I still can't seem to find it. Could it be unwillingness like you suggested? Seems unlikely to me as it does seem quite useful for some quick and dirty applications at the very least. Or maybe could it be that satisfactory implementations could not be made?

>Look at how much code Jackson uses for their core serialization

Is the problem complexity or bandwidth? You already have "dart:convert" in the browser, and has JSON, ASCII and you can even add your own formats to it, and it runs in the browser, now, what I can undertands is that you'll need to add mirrors as a requirement and mirros can be big, but again, don't you already need reflection for polymer?

It is really that a problem to instead of mapping JSON to a map have the chance to map to an Object<T>? I don't think it is a problem of complexity, but a problem of apathy, or "you don't really need that anyway" issue, and I hate when some one tries to tell me what I need and what I don't.

Apathy?

We created the JSON decoder in dart:convert, the serialization package, the protobuf compiler, and one of the JSON Schema based generators. Our largest internal customer created Streamy.

If you have an easy magical solution that fits more use cases that what we're already using in real production code, and also aren't affected by too much apathy, then we gladly accept contributions to the core SDK, and you can of course always publish your own package.

I'd be very interested in seeing what a team less apathetic that the ones that produced five serialization packages comes up with.

>We created the JSON decoder in dart:convert, the serialization package, the protobuf compiler, and one of the JSON Schema based generators

Great, then you already have 90% of the job done then.

>If you have an easy magical solution that fits more use cases that what we're already using in real production code

What are bug reports for?

>I'd be very interested in seeing what a team less apathetic that the ones that produced five serialization packages comes up with.

I don't know, but the 5 bugs I've submitted to Dart haven't been fixed yet, I submitted those almost 2 years ago all marked in the core as medium, so, you tell me, what conclusion should I make?

>>If you have an easy magical solution that fits more use cases that what we're already using in real production code >What are bug reports for?

If you have a bug report with the description of the behavior you want, then that's at least a start. My point is that I'm claiming there isn't an obvious one-size-fits-all solution, and that we've created several serialization packages, clearly demonstrating that we're not apathetic regarding serialization. To imply so is frankly insulting.

>I don't know, but the 5 bugs I've submitted to Dart haven't been fixed yet, I submitted those almost 2 years ago all marked in the core as medium, so, you tell me, what conclusion should I make?

That all projects of this magnitude have many open bugs? We have almost 4000 open issues out of 20,000 all time. Yes, many of those open issues are old, it's much easier to open them than close them, and some answers just aren't clear.

I assume these are your issues:

https://code.google.com/p/dart/issues/list?q=adrian

First, it's clear you've been using Dart from the start and that you've filed good reports, so thank you very much. There are 3 open out of 13 total.

The double.round() one is good, IMO. I don't know why it hasn't been addressed, other than the sheer volume of bugs we have. I would recommend that the squeaky wheel gets the oil. Sorry, but it's just reality with a large project and team. The other two I don't see clear consensus on, and the comments seem to indicate that the current behavior is intended. I personally agree with you on the Dart parse issue, but think that we shouldn't special case Completer, but instead work on union types.

I know that I'm not working in the next super text-editor, or in the next super-game, but I'm using Dart in a enterprice enviroment where numbers do matter, so If I see something as trivial as double.round not having what I need I really get demotivated, so, I'm sorry for getting emotional.

I'm using .NET in the server and if there is something MS does right is to listen to their enterprice customers, even if those customers do boring stuff like capturing forms and displaying numbers, but hey, those are important stuff for enterprices, same with the DateTime.parse, numbers and dates is an every day issue here, and is very important, and I'd like to see Dart also focusing in this type of market, we are alot.

The Completer bug I is also key for scalable projects, we, the ones using Dart, assume that the type safety part of Dart is reliable to do our work.

Anyway, I'm, glad at least one Dart developer is here to listen.

> Is the problem complexity or bandwidth?

Bandwidth is a prohibitive technical problem in this case. Complexity of such an API is a solvable problem in principle, but it will only get solved if a practical API can be made. My argument is that such an API cannot be made, because it will be too large, too fragile, or both.

> what I can undertands is that you'll need to add mirrors as a requirement and mirros can be big, but again, don't you already need reflection for polymer?

I don't know if Polymer.dart depends on mirrors, but it's irrelevant as neither Polymer or Mirrors are part of the core library.

> It is really that a problem to instead of mapping JSON to a map have the chance to map to an Object<T>?

Yes, because because reliably instantiating an arbitrary object with all data in the right place during runtime is just quite a hard problem in a static language. Available (de)serialization libraries demonstrate that.

> "I don't think it is a problem of complexity, but a problem of apathy, or "you don't really need that anyway" issue,"

My argument is that it's an issue of downsides not being worth the benefits. If this was possible in any practical way at all, I think it would be in there.

> and I hate when some one tries to tell me what I need and what I don't.

That's your problem, not a valid reason to criticise the Dart developers. Nobody is denying you anything. Your assumption that this is possible in the Dart core library in a practical sense is very likely simply wrong.

> My argument is that such an API cannot be made, because it will be too large, too fragile, or both

With that logic, why does Dart even has futures? I bet those are more complex and use more code, and yet, Dart have them, so I don't think it is about "being large and fragile".

>I don't know if Polymer.dart depends on mirrors, but it's irrelevant as neither Polymer or Mirrors are part of the core library

Since Dart developers are obsessed with Polymeter I wouldn't say is not relevant, and if they would have to make the JSON to Object<T> serialization in another library and not in the core then so be it, nobody is asking them to put it in the core.

> Yes, because because reliably instantiating an arbitrary object with all data in the right place during runtime is just quite a hard problem in a static language

They already have 90% of te job done, they have the JSON parser, they have mirrors, btw, JSON is a very simple format in the case you don't know, they already have mirrors to instantiate objects at runtime, they instantiate Maps, why can't they instantiate Objects with mirrors? is not logical, the other reflections libraries seem to work pretty well so, is not an excuse.

> My argument is that it's an issue of downsides not being worth the benefits

For who? maybe not for you, but for others it would.

> That's your problem, not a valid reason to criticise the Dart developers

Dart developers are humans and fallible, so they are not supergods or something, and Im not asking to put this in the core.

Wow, 90% really? It seems you figured it out. Maybe you should break through this appalling apathy and show them how it's done. After all, it's clear that your need should be catered to and these strangers providing things for free simply won't do it. Moreover, it's obviously only 10% of the work left, and less than the work on Futures. How hard can it be?

When I said 90% it is because the hard part is already done, and that hard part are mirrors, they already have the JSON parser too, so, they just have to put them together.

Anyway, since you are starting in using sarcasm and I'm not interested in that kind of argument, so we are done here.

I'm sorry about that. I thought we left serious conversation behind when you started asserting that most of the work was done (as Jackson shows, parsing and reflection are not the hard parts of a JSON-to-class library), and continued that apathy was still the most likely explanation. I thought I would have presented you enough evidence of the hardness of solving this problem, but you appear to be entitled enough to ignore it.

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