Dart (programming language)

Dart

Paradigm	Multi-paradigm: scripting, object-oriented (class-based), imperative, reflective, functional[1]
Designed by	Lars Bak and Kasper Lund
Developer	Google
First appeared	October 10, 2011 (2011-10-10)[2]
Stable release	1.18 / July 28, 2016 (2016-07-28)
Typing discipline	Optional
Platform	Cross-platform
OS	Cross-platform
License	BSD
Filename extensions	.dart
Website	www.dartlang.org
Major implementations
Dart VM, dart2js, Dartino, Flutter
Influenced by
JavaScript, Smalltalk, Erlang, Strongtalk, C#[3]

Dart is a general-purpose programming language originally developed by Google and later approved as a standard by Ecma (ECMA-408).^[4] It is used to build web, server and mobile applications, and for Internet of Things (IoT) devices.^[5] It is open-source software under a BSD license.

Dart is a class-based, single inheritance, object-oriented language with C-style syntax which can optionally transcompile into JavaScript. It supports interfaces, mixins, abstract classes, reified generics, and optional typing.

History

Dart was unveiled at the GOTO conference in Aarhus, Denmark, October 10–12, 2011.^[6] The project was founded by Lars Bak and Kasper Lund.^[7]

Standardization

Ecma International has formed technical committee TC52^[8] to work on standardizing Dart, and inasmuch as Dart can be compiled to standard JavaScript, it works effectively in any modern browser. Ecma International approved the Dart language specification first edition in July 2014, at its 107th General Assembly,^[9] and a second edition in December 2014.^[10]

Usage

There are four main ways to run Dart code:

Compiled as JavaScript

To run in mainstream web browsers, Dart relies on a source-to-source compiler to JavaScript. According to the project site, Dart was "designed to be easy to write development tools for, well-suited to modern app development, and capable of high-performance implementations."^[11] When running Dart code in a web browser the code is precompiled into JavaScript using the dart2js compiler. Compiled as JavaScript, Dart code is compatible with all major browsers with no need for browsers to adopt Dart. Through optimizing the compiled JavaScript output to avoid expensive checks and operations, code written in Dart can, in some cases, run faster than equivalent code hand-written using JavaScript idioms.^[12]

In the Dartium Browser

The Dart software development kit (SDK) ships with a version of the Chromium web browser modified to include a Dart virtual machine (VM). This browser can run Dart code directly without compiling to JavaScript. It is intended as a development tool for applications written in this language, rather than as a general purpose web browser.^[13] There were originally plans to include Dart support directly in Chrome, but these were cancelled.^[14]

Stand-alone

The Dart SDK also ships with a stand-alone Dart VM, allowing dart code to run in a command-line interface environment. As the language tools included in the Dart SDK are written mostly in Dart, the stand-alone Dart VM is a critical part of the SDK. These tools include the dart2js compiler, and a package manager suite called pub. Dart ships with a complete standard library allowing users to write fully working system apps, such as custom web servers.^[15]

Ahead-of-time compiled

Dart code can be AOT-compiled into machine code (native instruction sets). Apps built with Flutter, a mobile app SDK built with Dart, are deployed to app stores as AOT-compiled Dart code. ^[16]

Runtime modes

Dart programs run in one of two modes. In checked mode, which is not the default mode and must be turned on, dynamic type assertions are enabled. These type assertions can turn on if static types are provided in the code, and can catch some errors when types do not match. For example, if a method is annotated to return a String, but instead returns an integer, the dynamic type assertion will catch this and throw an exception. Running in checked mode is recommended for development and testing.

Dart programs run by default in production mode, which runs with all dynamic type assertions turned off. This is the default mode because it is the fastest way to run a Dart program.

Isolates

To achieve concurrency, Dart uses isolates, which are independent workers that do not share memory, but instead use message passing. This is similar to Erlang actors. Every Dart program uses at least one isolate, which is the main isolate. When compiled to JavaScript, isolates are transformed into Web workers.

Snapshots

Snapshots are a core part of the Dart VM. Snapshots are files which store objects and other runtime data.

Script snapshots

Dart programs can be compiled into snapshot files. These files contain all of the program code and dependencies preparsed and ready to execute. This allows fast startups.

Full snapshots

The Dart core libraries can be compiled into a snapshot file which allows fast loading of the libraries. Most standard distributions of the main Dart VM have a prebuilt snapshot for the core libraries which is loaded at runtime.

Object snapshots

Dart is a very asynchronous language. With this, it uses isolates for concurrency. Since these are workers which pass messages, it needs a way to serialize a message. This is done using a snapshot, which is generated from a given object, and then this is transferred to another isolate for deserializing.

Native mobile apps

Google is working on full Dart stacks for native mobile app development on both Android and iOS.^[17]

Compiling to JavaScript

The first compiler to generate JavaScript from Dart code was dartc, but it was deprecated. The second Dart-to-JavaScript compiler was Frog. It was written in Dart, but never implemented the full semantics of the language. As of 2015, the third Dart-to-JavaScript compiler is dart2js, from Google. An evolution of earlier compilers, it is written in Dart, and intended to implement the full Dart language specification and semantics.

On March 28, 2013, the Dart team posted an update on their blog addressing Dart code compiled to JavaScript with the dart2js compiler,^[18] stating that it now runs faster than handwritten JavaScript on Chrome's V8 JavaScript engine for the DeltaBlue benchmark.^[19]

Editors

On November 18, 2011, Google released Dart Editor, an open-source program based on Eclipse components, for Mac OS X, Windows, and Linux-based operating systems.^[20] The editor supports syntax highlighting, code completion, JavaScript compiling, running web and server Dart applications, and debugging.

On August 13, 2012, Google announced the release of an Eclipse plugin for Dart development.^[21]

On April 18, 2015, Google announced that the Dart Editor would be retired in favor of the JetBrains integrated development environment (IDE),^[22] which is now the recommended IDE for the language. The Dart plugin^[23] is available for IntelliJ IDEA, PyCharm, PhpStorm and WebStorm. This plugin supports many features such as syntax highlighting, code completion, analysis, refactoring, debugging, and more. Other plugins are available for editors like Sublime Text, Atom, Emacs, Vim and Visual Studio Code.^[24]

Chrome Dev Editor

It has been known since November 2013^[25] that the Chromium team is working on an open source, Chrome App-based development environment with a reusable library of GUI widgets, codenamed Spark, later renamed as Chrome Dev Editor.^[26] It is built in Dart, and contains Spark which is powered by Polymer.^[27] A developer preview version is available in the Chrome Web Store.

DartPad

The Dart team created DartPad at the start of 2015, to provide an easier way to start using Dart. It is a fully online editor from which users can experiment with Dart application programming interfaces (APIs), and run Dart code. It provides syntax highlighting, code analysis, code completion, documentation, and HTML and CSS editing.^[28]

SIMD on the web

In 2013, John McCutchan announced that he had created a performant interface to single instruction, multiple data (SIMD) instruction sets for Dart, bringing the benefits of SIMD to web programs for the first time, for users running Google's experimental Dartium browser.^[29] The interface consists of two types:

• Float32×4, 4× single precision floating point values
• Uint32×4, 4× 32-bit unsigned integer values

Instances of these types are immutable and in optimized code are mapped directly to SIMD registers. Operations expressed in Dart typically are compiled into one instruction with no overhead. This is similar to C and C++ intrinsics. Benchmarks for 4×4 matrix multiplication, 3D vertex transformation, and Mandelbrot set visualization show near 400% speedup compared to scalar code written in Dart.

Example

A Hello World example:

main() {
  print('Hello World!');
}

A function to calculate the nth Fibonacci number:

int fib(int n) => (n > 2) ? (fib(n - 1) + fib(n - 2)) : 1;

void main() {
  print('fib(20) = ${fib(20)}');
}

A simple class:

// Import the math library to get access to the sqrt function.
import 'dart:math' as math;

// Create a class for Point.
class Point {

  // Final variables cannot be changed once they are assigned.
  // Create two instance variables.
  final num x, y;

  // A constructor, with syntactic sugar for setting instance variables.
  Point(this.x, this.y);

  // A named constructor with an initializer list.
  Point.origin()
      : x = 0,
        y = 0;

  // A method.
  num distanceTo(Point other) {
    var dx = x - other.x;
    var dy = y - other.y;
    return math.sqrt(dx * dx + dy * dy);
  }

  // Example of Operator Overloading
  Point operator +(Point other) => new Point(x + other.x, y + other.y);
}

// All Dart programs start with main().
void main() {
  // Instantiate point objects.
  var p1 = new Point(10, 10);
  var p2 = new Point.origin();
  var distance = p1.distanceTo(p2);
  print(distance);
}

Influences from other languages

Dart is a descendant of the ALGOL language family,^[30] alongside C, Java, C#, JavaScript, and others.

The method cascade syntax, which provides a syntactic shortcut for invoking several methods one after another on the same object, is adopted from Smalltalk.

Dart's mixins were influenced by Strongtalk^[31] and Ruby.

Dart makes use of isolates as a concurrency and security unit when structuring applications.^[32] The Isolate concept builds upon the Actor model, which is most famously implemented in Erlang.

The Mirror API for performing controlled and secure reflection was first proposed in a paper^[33] by Gilad Bracha (who is a member of the Dart team) and David Ungar and originally implemented in Self.

Criticism

Dart initially had a mixed reception and the Dart initiative has been criticized by some for fragmenting the web, due to the original plans to include a Dart VM in Chrome. Those plans were dropped to focus instead on compiling Dart to JavaScript.^[14]

See also

• CoffeeScript
• Fantom (programming language)
• Go, another language developed by Google
• Google Web Toolkit
• Haxe, a language that can be compiled to JavaScript and several other languages
• Opa (programming language)
• Pyjamas (software)
• TypeScript
• AtScript

References

Bibliography

External links

• Official website
• Bullseye:Your first Dart App by Seth Ladd and Jaime Wren
• A Walk on the Dart Side: A Quick Tour of Dart (November 2011) — Lecture given at Stanford University by Google software engineer Gilad Bracha (video archive, YouTube, transcript)
• Fletch: Experiment for Dart for embedded development
• The Dartosphere – Aggregation of Dart Language related blogs