Frequently Asked Questions (FAQ)

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Updated June 2017

This page collects some of the top questions we’ve heard from the community since Dart was open sourced. For other questions and answers, see:

General

Q. Is Dart under the control of a standards body?

Yes. As of December 2013, Ecma TC52 has been put in charge to own, evolve, and publish the standard specification of the Dart language. In addition to TC52, we have also introduced a process for submitting Dart enhancement proposals (DEP), because we wanted to make it easier to contribute to and follow the evolvement of Dart.

Q. How are you taking input on changes to the Dart repository?

We listen to feedback and issues, and we review patches from contributors. A contributor with a good track record can become a committer to the repository. Google engineers will also be working in the public repository, making visible changes. The project is lucky to have received many external patches and has welcomed distributed committers.

Q. Why didn’t Google make Dart an open standard right from the start?

We’re taking the usual route to get to an open-standard programming language: someone creates a coherent first version, people experiment with it, and we standardize later. The open standard web platform has been known to add other pieces this way, where standardization follows after a vendor experiment: canvas, for example. We understand that this route raises concerns, but we think it is sometimes useful, and in particular that it is useful for programming languages, where design by committee is risky.

The most recent successful language designed by an open committee was Haskell, starting in 1990. The most widely used was COBOL, followed by Ada. It’s not a common way to do language design. Among dozens and dozens of major languages, six (give or take a couple of debatables) were designed this way. (And one of those six was ALGOL-68.)

Q. Why didn’t Google build a bytecode VM targetable by multiple languages including Dart?

Each approach has advantages and disadvantages, but we feel that in the context of Dart it made sense to build a language-specific VM for the following reasons:

  • Google already works on a multi-language bytecode: LLVM bitcode in PNaCl.

  • Even if a bytecode VM is specialized for Dart, a language VM will be simpler and faster because it can work under stronger assumptions—for instance, a structured control flow. These assumptions make the implementation cleaner and optimizations easier.

  • A general-purpose bytecode VM would be even larger and slower, as it generalizes assumptions and adds functionality that for Dart is dead code: for example, multithreading with a shared heap.

  • No bytecode VM is truly general-purpose; they all make assumptions that privilege some class of languages. A language VM leaves more room to improve the VM and make deep changes to optimization of the language. Some Dart engineers wrote an article talking about the VM question in more detail.

Language

Q. How does Dart relate to Go?

Dart and Go are both language projects started at Google, but they are independent and have different goals. As a result, they make different choices, and the languages have very different natures, even while we all try to learn from each others’ work.

Q. Why isn’t Dart more like Haskell / Smalltalk / Python / Scala / other language?

Various reasons, depending on the language being asked about.

For languages that are quite different from JavaScript: it’s important for Dart to compile to efficient JavaScript. Our experience in GWT is that if the source language is too different from JavaScript, it creates some cases where complex output code is needed to emulate the source language’s behavior. This can cause performance to vary in ways that are not transparent to the programmer.

For languages that are less mainstream: we expect that modeling Dart on these would, on the whole, hurt our adoption. Our team includes fans of these languages, and if we thought Dart could take up our favorite cool language features and push them to widespread adoption we might be tempted, but really we think we’ve got our hands full introducing a new language at all.

For languages that are “more dynamic” than Dart: Dart deliberately trades off some of this arbitrary runtime modification for the goal of better performance and tools.

Q. Why isn’t Dart syntax more exciting?

We did throw in some nice syntactic features such as this. constructor args and => for one-line functions, but we’d agree that Dart chooses familiarity over excitement. One team member’s personal testimonial: “I wish it had a little more razzle dazzle but I can’t deny that literally on my first day of writing Dart code, I was productive in it.”

Q. Does Dart have reflection capabilities?

We have reflection support from the mirrors API.

Q. Can Dart add tuples, pattern matching, non-nullable types, partial evaluation, optional semicolons, …?

The language is now at 1.x, but we anticipate further language evolution to occur in a standards group. It might be able to include your feature, although it can’t include everything. Some features don’t fit the basic nature of the language, and some don’t play well with other features. Simplicity is the single most important gift we all can give to future programmers.

Please look at the list of Dart issues to see if your request is already there, and add a new issue if not. Make a thoughtful argument for your feature. Sample code with and without your feature is good evidence; a sizeable codebase that shows the need is even better evidence.

Please don’t be surprised if the Dart designers say “no” by default, especially for now. It’s far more painful to remove a language feature than to add it, so Dart is likely to add the most obvious features first, and then revisit the next tier later. And there simply are more possible language features in the world that can fit into any single language without making a total hash of it. But we do very much appreciate suggestions and evidence. We hope you’ll see our appreciation through careful design choices and fair communication about them.

Types

Q. Is Dart a type-safe language?

Dart is a type-safe language if you opt in to strong mode. Strong mode enables a sound static type system and is used by Flutter (a cross-platform mobile development system), and the Dart Development Compiler (DDC).

Even in strong mode, though, you can annotate any variable with dynamic if you need the flexibility of a dynamic language. dynamic can contain any type. Of course, that removes many of the benefits of a type-safe language for that variable.

Without strong mode enabled, Dart is not a type-safe language.

Q. What is strong mode?

Strong mode is Dart’s implementation of a sound type system. With strong mode enabled (in an implementation that has both the static and runtime checks), Dart is a type safe language ensuring that static type annotations are actually correct at runtime.

For more information, see Strong Mode Dart.

Q. Why are generics covariant?

Covariant generics fit a common intuition that programmers have, and very often this intuition is correct, such as in the common “read-only” use of a generic. Although this intuition isn’t always correct, Dart doesn’t need it to be. Dart has already chosen optimistic static checking, so why not continue down that path and allow covariant uses of generics to pass static type checking?

Where covariant generics are too optimistic, Dart’s type-safe execution allows the static warnings to be optimistic without being dangerous. Although covariance can be pessimistic too, we think it will be rare that people run into that, and and there’s a simple workaround for any pessimism.

We are familiar with a variety of ways that languages try to mark or infer variance. We don’t think any of them are suitable for Dart, where we want type annotations to be optional and unobtrusive: it wouldn’t fit to require marking, and we feel that variance inference systems add too much complexity for their benefit in Dart.

Again, we’re trying to be pragmatic, and we think the outcome is reasonable.

Usage and tools

Q. Does Dart support JSON?

Yes. See the JSON converters in the dart:convert library.

Q. Can Dart run on the server?

Yes. See Dart on the Server for details.

Q. How do I use third party code, or share code?

You can find many packages on pub.dartlang.org, a service for hosting packages of Dart code. Use the pub command to package your code and upload to pub.dartlang.org.

Q. Do I need to use a particular editor or IDE to write Dart code?

Nope. You can try out Dart code with DartPad, and then use your favorite editor or IDE for real development. Some full-featured IDEs such as IntelliJ IDEA and WebStorm have Dart plugins. Dart plugins also exist for Sublime, VIM, Emacs, and other editors. We used to provide a Dart-specific editor called Dart Editor, but as of 1.11 Dart Editor is no longer available. For more information, see Dart Tools.

Q. Can I build an Android app with Dart?

Yes! You can build an Android app that also works on iOS from a single codebase using Flutter.

Q. What are some real-world production deployments of Dart?

Google AdWords, AdSense, and AdMob all use Dart. More than 75% of Google’s revenue flows through these apps. See Who Uses Dart for a more complete list.