Introduction to Google's Dart Programming language, with a brief overview of the major language features.

1. I N T R O D U C T I O N T O D A R T
R A M E S H N A I R
H I D D E N TA O . C O M
!
M A Y 3 0 , 2 0 1 4
TA I P E I J A VA S C R I P T E N T H U S I A S T S

2. W H AT I S D A R T ?
• Dynamic scripting language (runs in a VM)
• lntended as successor to Javascript
• Better performance, better tooling, better for larger projects
• Built by people who built V8 and Java HotSpot
• Oct 2011: Announced by Google
• Nov 2013: Stable v1.0 release
• Dec 2013: Setup ECMA TC52 for standardisation
• www.dartlang.org
• gist.github.com/paulmillr/1208618

3. G E T D A R T
• dartlang.org/tools/download.html
• Dart IDE (based on Eclipse)
• Dartium (version of Chromium with Dart VM)
• SDK
• dart - command-line standalone VM
• dart2js - compile to JS
• dartanalyzer - static code analyzer, spots bugs
• pub - community package manager
• docgen - API docs generator

4. T H E B A S I C S
L E T ’ S B E G I N …

5. A S I M P L E P R O G R A M
// short-hand function notation + parameter type and return types
double show(double v) => v * 2.0;
!
// program entry point, with void return type
void main() {
// dynamic type
var a = 2.222;
print("Result: ${show(a)}"); /* Result: 4.444 */
!
// everything is an object
assert(a is Object);
!
// converting to other types
print(a.toInt() is int); /* true*/
print(a.toString() is String); /* true */
print(double.parse(a.toStringAsFixed(1))); /* 2.2 */
}

6. O P T I O N A L T Y P E A N N O TAT I O N S
• Help your IDE and other tools help you
• Let the “static checker” warn you about potential
problems, though code will still compile
• Can help improve performance when compiling to JS
• At runtime type annotations are only used if the Dart
VM is in “Checked” mode…
// either is ok
int a = 12;
var b = 12;

7. D A R T R U N T I M E M O D E S
• Checked mode
• VM inserts type assertion checks at runtime
• Will throw exception if types don’t match up:
• If expecting type A then you can use an item which is type A
or any of A’s subtypes.
• Will throw exception if an assert() statement fails
• Production mode (default)
• Ignores all type annotations
• Better performance because no type checks needed
• Ignores all assert() statements

8. F U N C T I O N D E F I N I T I O N
var loudify = (msg) => '!!! ${msg.toUpperCase()} !!!';
print(loudify('hello')); /* !!! HELLO !!! */
void show({firstName: 'Foo', lastName: 'Bar'}) {
print("${firstName} ${lastName}");
}
!
show('Mark'); /* throws Exception */
show('Mark', 'Twain'); /* throws Exception */
show(firstName: 'Mark'); /* Mark Bar */
show(lastName: 'Twain'); /* Foo Twain */

9. T Y P E D E F S
typedef int Compare(int a, int b);
!
int comp1(int a, int b) => a - b;
!
int comp2(bool a, int b) => a - b;
!
String run(Compare sortFunction) => 'ok';
!
void main() {
print(comp1 is Function); /* true */
print(comp1 is Compare); /* true */
!
print(run(comp1)); /* ok */
!
print(run(comp2)); /* throws TypeError */
}

10. A N D T H E R E S T…
• Closures - similar to Javascript
• Operators - Arithmetic, logic, assignment, bitwise,
comparison, etc.
• Collections - lists (like Javascript arrays), sets, maps
• Control flow - if-else, for/do-while, switch-case
• Exceptions - throw, catch, finally
• Reflections API
• Typed data, SIMD, etc.

11. O B J E C T
O R I E N T E D
P R O G R A M M I N G
A R C H I T E C T U R E

12. B A S I C C L A S S E S
class StrRep {
String str;
String finalStr;
num count;
// constructor with initializer list
StrRep(this.str, this.count);
!
build() => finalStr = str.trim().toUpperCase() + count.toString();
void display() => print(this.finalStr);
}
!
void main() {
// use the cascade operator (..)
new StrRep('NaN ', 3)
..build()
..display(); /* NAN3 */
}

13. G E T T E R S A N D S E T T E R S
class Box {
num _top;
!
Box(this._top);
num get top => _top;
set top(num value) => _top = value * 2;
}
!
main() {
var box = new Box(5);
print(box.top); /* 5 */
box.top = 5;
print(box.top); /* 10 */
}

14. FA C T O RY / S I N G L E T O N
class Store {
var data;
static Store _cache = null;
// visible constructor
factory Store() {
if (null == _cache) {
_cache = new Store._internal();
}
return _cache;
}
// hidden constructor
Store._internal();
}
!
void main() {
new Store().data = 'secret stuff';
var b = new Store();
print(b.data); /* secret stuff */
}

15. O P E R AT O R O V E R L O A D
class Vector {
final int x;
final int y;
Vector(this.x, this.y);
!
// Override + (a + b).
Vector operator +(Vector v) {
return new Vector(x + v.x, y + v.y);
}
}
!
main() {
// final = cannot modify this variable after this
final v = new Vector(2,3);
final w = new Vector(2,2);
!
assert((v+w).x == 4 && (v+w).y == 5); // v+w == (4,5)
}

16. S I M P L E I N H E R I TA N C E
class Shape {
void draw() => print('shape');
}
!
class Rectangle extends Shape {}
!
class Square extends Rectangle {
void draw() => print('square');
}
!
void main() {
new Rectangle().draw(); /* shape */
new Square().draw(); /* square */
}

17. G E N E R I C S
class Cache<T> {
Map<String,T> _m;
Cache() {
_m = new Map<String, T>();
}
T get(String key) => _m[key];
set(String key, T value) => _m[key] = value;
}
!
void main() {
var c = new Cache<String>();
c.set('test', 'value');
print(c.get('test') == 'value');
c.set('test', 43); // fails in checked mode
}
Love this? read C++ Template Metaprogramming

18. M O R E O O P…
• Implicit Interfaces - if you implement a class then it
becomes a specification
• Abstract classes - if you don’t want the parent class to
ever be instantiated make it abstract
• Mixins - if you want to inherit from more than one class
this helps

19. L I B R A R I E S
A N D
PA C K A G E S
S H A R I N G C O D E

20. L I B R A R I E S
NOTE: Identifiers that start with underscore (_) are not
visible outside the library
library calc; // optional
!
int _add(int x, int y) => x + y;
!
int sum3(int x, int y, int z) => _add(_add(x,y), z);
import './calc.dart';
!
void main() {
print(sum3(11, 12, 13)); /* 36 */
print(_add(11, 12)); /* throws NoSuchMethodError */
}

21. B U I LT- I N L I B R A R I E S
// only show certain items
import "dart:math" as Math show PI;
!
// hide certain items
import "dart:collection" as Collection hide LinkedList;
!
void main() {
print(Math.PI); /* 3.14 */
print(Math.E); /* throws exception */
new Collection.LinkedList(); /* throws exception */
}
• dart:core is always automatically imported
• More at: https://api.dartlang.org/apidocs/channels/
stable/dartdoc-viewer/home

22. C O M M U N I T Y L I B R A R I E S
name: example
description: A sample command-line application
dependencies:
quiver: any
• pub.dartlang.org
• Command-line package manager: pub
$ p u b g e t
!
Resolving dependencies...
Got dependencies!
• Step 1 - specify dependencies in pubspec.yaml:
• Step 2 - install dependencies:

23. A S Y N C H R O N O U S
P R O G R A M M I N G
A L L A T O N C E …

24. T H E “ G A M E ” L O O P

25. A D D I N G A M I C R O TA S K
• Can directly add to the microtask queue
• Use scheduleMicrotask(fn)
• Will ensure your task runs before the next event
queue item
!
• BUT this delays event processing
• Use the event queue (i.e. a Future) when possible.

26. F U T U R E S
• Known as “Promises” in Javascript
• Futures get added to the event queue
• API can wrap sync methods, wait for multiple Futures, etc.
import “dart:async";
!
Future result = costlyQuery();
!
result
.then((value) => expensiveWork(value))
.then((value) => lengthyComputation(value))
.then((value) => print(value))
.catchError((exception) => print('DOH!'))
.whenComplete(closeConnection); // may return a Future

27. S T R E A M S
• Produce one or more events that listeners receive
• Two types
• Broadcast - multiple listeners, doesn’t wait for listeners
before sending
• Single-subscription - one listener, queues events and awaits
a listener
• Can be paused (will buffer events until unpaused)
• Can be proxied and transformed (e.g. music processing)
• Auto-unsubscribe listeners when ‘done’ event sent

28. E X A M P L E S T R E A M
import 'dart:async';
!
main() {
var data = [1,2,3,4,5]; // some sample data
var stream = new Stream.fromIterable(data);
!
// subscribe to the streams events
stream.listen((value) { //
print("Received: $value"); // onData handler
}); //
}

29. I S O L AT E S
• Isolate - light-weight unit of concurrency
• Each has its own memory and “thread of control”
• Uses message passing to communicate with others
• Main app always runs within its own isolate
• Standalone Dart VM always runs isolates in parallel,
using all available CPU cores (yay!)
• Browser Dart VM may use web workers, thought not
every browser implementation may do this

30. // alice.dart
!
import "dart:async";
import "dart:isolate";
!
void main() {
var response = new ReceivePort();
Future<Isolate> remote =
Isolate.spawnUri(Uri.parse("bob.dart"), ["foo"],
response.sendPort);
remote.then((_) => response.first)
.then((msg) { print("received: $msg"); });
}
// bob.dart
!
import "dart:isolate";
!
void main(List<String> args, SendPort replyTo) {
replyTo.send(args[0]);
}

31. O T H E R A S Y N C S T U F F…
• Futures - delaying execution, waiting for multiple
• Streams - testing event before handling it
• Zones - asynchronous dynamic extents
• Timers
• I/O

32. B U I L D I N G
W E B
A P P S
H T M L + J A VA S C R I P T

33. E M B E D I N H T M L
<!-- For browsers with the Dart VM -->
<script type='application/dart' src='app.dart'></script>
!
<!-- For browsers without Dart VM, will fetch app.dart.js -->
<script src="packages/browser/dart.js"></script>
1. Compile into JS
$ d a r t 2 j s - o a p p . d a r t . j s a p p . d a r t
2. Add to end of HTML body
• main() invoked after DOM content is loaded.
• One Dart script per page. Do not use inline scripts, async/
defer, or rely on injection of code or ordering of scripts

34. K N O W Y O U R B L O AT
void main() {
print('Hello, World!');
}
• dart2js output: 14,334 bytes
• Browser package (dart.js): 1,270 bytes
!
• Total: 15,645 bytes (~15 KB)
• And don’t forget app startup time
• Dart source: 41 bytes

35. C A L L I N T O J AVA S C R I P T
import 'dart:js';
!
void main() {
var p1 = new JsObject(context['Point'], [5, 1]);
!
p1['x'] = 100;
print(p1['x']); // Prints 100.
var p2 = new JsObject(context['Point'], [1, -2]);
print(p1.callMethod('distanceFrom', [p2]));
}
var Point = function(x, y) {
this.x = x;
this.y = y;
this.distanceFrom = function(otherPoint) {
return Math.sqrt(Math.pow(otherPoint.x - this.x, 2) +
Math.pow(otherPoint.y - this.y, 2));
};
};

36. D O M I N T E R A C T I O N S
import "dart:html";
!
void main() {
// returns List<Element>
var buttons = document.querySelectorAll('.clearfix');
// attributes = Map<String,String>
buttons[0].attributes.remove('name');
var newElem = new ButtonElement()
..id = 'mozillaBtn'
..classes.add('mozilla') // Set<String>
..text = 'Mozilla';
document.nodes.add(newElem);
// events are streams
newElem.onClick.listen( (event) => print('click!') );
}

37. C H E C K O U T…
• Polymer - web components
• AngularDart (port of Angular.js)
• JSON serialization/de-serialization
• HttpRequest (like XMLHttpRequest)
• IndexedDB
• SVG
• Web audio, WebGL

38. P E R F O R M A N C E
V S
J AVA S C R I P T
D A R T …

39. J AVA S C R I P T C O M PA R I S O N
• https://www.dartlang.org/performance/
• Dart always faster than Javascript
• dart2js output mostly slower than Javascript
• http://www.techempower.com/benchmarks/
• Server-side Dart still mostly slower than Node.js
But why does Dart perform better?

40. W H Y D A R T P E R F O R M S B E T T E R
• Simpler object model
• Straightforward language semantics
• Fewer special corner cases to worry about
• e.g. Can’t modify Object prototype at runtime
• More predictable performance
• Better memory utilisation
• Less generated code

41. F I N D O U T M O R E …
• https://www.youtube.com/watch?v=huawCRlo9H4
• Google I/O 2013 talk on Dart and JS VM
performance
• Also talks about work needed to ship Dart VM with
Chrome browser

42. PA R A L L E L P R O C E S S I N G
• SIMD
• “Single Instruction Multiple Data”
• Float32x4, Int32x4
• Operate on numbers in parallel
• Efficient CPU usage
• Potential speedup of 400% over
non-parallel computation
• Useful for 3D graphics, audio
processing, etc.

43. T H E
F U T U R E
L O O K T O …

44. W H O I S U S I N G I T N O W ?
• drone.io - Continuous integration server
• worktrail.net - time tracking app
• Spark - Chrome app-based IDE
• anionu.com - cloud security
• …many more
!
• https://www.dartlang.org/community/who-uses-dart.html

45. B R O W S E R S U P P O R T
• Chrome: Coming soon, need to implement new DOM-to-VM
memory management model first.
• Firefox: "Most browsers have no reason to include Dart because
doing so would not only be extremely difficult for engineers to
accomplish in each major browser, it would also result in a quality
hit,”
• Safari: ”Two runtimes sharing the DOM adds both bug habitat
and a performance tax”
• IE: "In practice, JavaScript performance is not the bottleneck in
real-world performance”.
• Microsoft are banking on TypeScript, a language which
translates to Javascript

46. @ H I D D E N TA O
That’s all folks!