Google Dart

Google Dart Eberhard Wolff Architecture & Technology Manager adesso AG27.10.11

Dart: A Structure Web Programming Language►  New programming language►  New programming tools►  New open source project►  Currently in a preview►  …for feedback27.10.11

The Team Behind Dart ►  Lars Bak >  Beta language >  HotSpot Java VM >  V8 JavaScript VM in Google Chrome >  18 software patents ►  Gilad Bracha >  Computational Theologist and later Distinguished Engineer at Sun >  Java Language Specification >  Java Virtual Machine Specification ►  Both worked on Strongtalk (Smalltalk + static typing)27.10.11 3

Why Dart?►  More and more web application with complex logic►  Will become a lot more: HTML5 on the rise►  So far: No really great languages designed to create large scale web applications►  Google: The competition is NOT JavaScript ... but fragmented mobile platforms►  GWT (Google Web Toolkit) already featured a Java to JavaScript compiler►  Dart is designed with simplicity and mass appeal in mind27.10.11 4

Runtime Environment►  Dart has its own VM►  Open Source project►  Needed for some advanced features►  Dart can compile into JavaScript►  Runs on any browser►  Currently not very efficient►  i.e. about the same performance as first V8 releases►  Size of JavaScript code currently considerable27.10.11 5

Hello World in Dart main() { print(Hello, Dart!); } ►  C like language int fib(int n) { if (n <= 1) return n; return fib(n - 1) + fib(n - 2); } main() { print(fib(20) = ${fib(20)}); } ►  Seemingly static typing27.10.11

Objects and Classes class Person { String name; Person(this.name); } main() { Person p = new Person(Gilad); print(Hi ${p.name} ); } ►  Easy to initialize fields27.10.11 7

Objects and Classes class Person { String name; String firstname; Person(this.name); Person.withFirstname(this.firstname,this.name); } main() { Person p = new Person.withFirstname(Gilad,Bracha); print(Hi ${p.firstname} ${p.name}); } ►  No method or constructor overloading27.10.11 8

Namespaces►  Much like Java packages►  Might contain classes, interfaces, variables and functions►  Definition:#library("http"); ►  Using:#import("http.dart"); ►  Optional prefix:#import("http.dart”,”http”); 27.10.11 9

Dart Library27.10.11 10

Object Construction With Factoriesinterface Person class Adessi factory PersonFactory { implements Person { Person(name); Adessi(this.name); final name; String name; } } class PersonFactory { class RealPerson factory Person(name) { implements Person { if (name == Wolff) { RealPerson(this.name); return new Adessi(name); String name; } } return new RealPerson(name); } main() { } Person p = new Person(Wolff); print(p is Adessi); p = new Person(Bracha); ►  Very elegant approach to allow for other object print(p is Adessi); creation algorithms } 27.10.11 11

More Complex Example class Person {} class Customer extends Person { buy() {print("bought");} } main() { Person p = new Customer(); p.buy(); } 27.10.11 12

More Complex Example class Person {} class Customer extends Person { buy() {print("bought");} } main() { Person p = new Customer(); p.buy(); } ►  Code actually compiles and runs►  There are no type errors – only Static Warnings►  Types are considered annotations►  Type annotations never change the semantics of a program27.10.11 13

On Types►  Type theory: A type defines a set of values and operations on them >  i.e.Java int: values: all integers from -2147483648 to 2147483647 >  Operations on int: + - * etc►  Goal: Check types to find errors >  i.e. multiply a String by an int >  i.e. call a method that does not exist on an object►  Type checkers proof the partial correctness of programs►  i.e. at least types are correct►  Typing will only find basic errors27.10.11 14

Dynamic Typing►  At runtime►  Advantage >  Simpler >  More flexible >  Can even implement methods on the fly – Meta programming►  Disadvantage >  Perceived as less secure27.10.11 15

Static Typing►  Typing checked At compile time►  Advantage >  IDE support >  Documentation >  Perceived as safer >  …but problems should be found by Unit Tests, too!►  Disadvantage >  Overhead if no type inference >  Complex to get right in some case >  Complex (Java Generic FAQ by Anglika Langer is 297 pages !)27.10.11 16

Generics in Java►  Does this code compile? public class Customer extends Person { … } public static void main(String[] args) { List<Person> listOfPerson = new ArrayList<Person>(); List<Customer> listOfCustomer = new ArrayList<Customer>(); listOfCustomer=listOfPerson; listOfPerson=listOfCustomer; } 27.10.11 17

Generics in Java►  Does this code compile? public class Customer extends Person { … } public static void main(String[] args) { List<Person> listOfPerson = new ArrayList<Person>(); List<Customer> listOfCustomer = new ArrayList<Customer>(); listOfCustomer=listOfPerson; listOfPerson=listOfCustomer; } listOfPerson.add(new Person()); listOfCustomer.add(new Person()); Customer c = listOfCustomer.get(1); Customer c = listOfPerson.get(1); 27.10.11 18

Generics and Static Typing in Java►  You can still mess with it►  Basically each type cast disables static typing►  i.e. it can introduce problems that otherwise would have been discovered by the compiler listOfPerson.add(new Person()); Object obj = listOfPerson; listOfCustomer = (List<Customer>) obj; Customer c = listOfCustomer.get(0); 27.10.11 19

Static vs. Dynamic Typing: My Take►  Errors found by a static type checker will also be found by unit tests►  The security of static typing is only perceived►  Real advantage: Documentation►  “I expect you to pass in a Customer!”►  “This gives you a Person!”►  Tool support►  Easier to come up with suggestions for content assist►  However, Dynamic languages tools are catching up27.10.11 20

Generics in Dart class Person {} class Customer extends Person { buy() {print("bought");} } main() { List<Customer> listOfCustomer = new List<Customer>(); List<Person> listOfPerson = listOfCustomer; listOfPerson.add(new Person()); Customer c = listOfCustomer[0]; c.buy(); } 27.10.11 21

Generics in Dart class Person {} class Customer extends Person { buy() {print("bought");} } main() { List<Customer> listOfCustomer = new List<Customer>(); List<Person> listOfPerson = listOfCustomer; listOfPerson.add(new Person()); Customer c = listOfCustomer[0]; c.buy(); } ►  Call to buy() won’t work►  Problem not found until the method is actually called►  Optional run time type checker would find the problem one line earlier►  Valid code: List<Customer> is a List<Person>27.10.11 22

Generics in Dart►  Generics in Dart are considered covariant►  i.e. List<Customer> is List<Person>►  This is in fact logical incorrect (see last slide)►  But: >  Do you want to read 297 pages Generic FAQ? >  And: It is just a help to spot basic errors27.10.11 23

Concurrency public class MyCache { Map<Integer, Integer> map = new HashMap<Integer, Integer>(); public void add(int i, int j) { map.put(i, j); } public int read(int i) { return map.get(i); } }►  What is the problem?27.10.11 24

Concurrency public class MyCache { Map<Integer, Integer> map = new HashMap<Integer, Integer>(); public void add(int i, int j) { map.put(i, j); } public int read(int i) { return map.get(i); } }►  What is the problem?►  Code is not thread safe!►  Should use ConcurrentHashMap instead27.10.11 25

Concurrency►  What is the real problem? Threads►  Concurrency in object-oriented systems►  OO is based on concurrent access shared state >  Hard to get correct >  If you get it correct: performance bad >  Locks >  Synchronization >  Etc Object with State►  Pretty low level concept►  This is why Carnegie Mellon dropped OO from the Computer Science curriculum!►  Can we do better?27.10.11 26

Dart code is always single threaded!27.10.11 27

Isolates►  Inspired by Actor model►  As present in Erlang►  As done in Scala with Actors and Akka Port►  Idea: State is hidden in Isolates Isolate with State►  Isolates communicate with messages send to ports►  Each isolate only works on one message at a time►  No concurrency issues in an Isolate: Only one thread►  Still concurrent: Multiple isolates might be active at a time27.10.11 28

Isolates class Printer extends Isolate { main() { port.receive((message, replyTo) { if (message == null) port.close(); else print(message); }); } } main() { new Printer().spawn().then((port) { for (var message in [Hello, from, other, isolate]) { port.send(message); } port.send(null); }); } 27.10.11 29

More Fun With Isolates►  Isolates might be mapped to Web Worker in JavaScript►  Nothing is shared►  Isolates will have their own heap on the Dart VM >  Messages must be serialized and deserialized >  Garbage Collection can happen per Isolate >  No more stop-the-world GC!►  Isolates might be used to introduce security concepts >  Enforce security rules on ports >  To replace Same Origin Policy27.10.11 30

More Fun With Isolates►  Isolates require a light weight concurrency model >  OS Thread switches take too much time >  In Erlang 100.000 of Isolates equivalent are not uncommon >  No way to run that many threads >  Interesting issue for Dart VM►  Isolates for Remoting >  Can send messages to a port on a different host >  Semantics don’t change as serialization is done anyway►  Probably more high level concurrency models►  Specifications says that Isolates might run different versions of libraries27.10.11 31

Even More Fun With Isolates►  In Erlang the concept is extended for high availability >  Links allow to listen to events of Isolates >  Supervisor can monitor other processes >  If an error occurs the isolate crashes and is restarted >  Hierarchies of supervisors can be created >  State is a problem here >  This makes high availability easy to develop >  Dart might come up with a similar solution27.10.11 32

Snapshots►  VM can be snapshot►  Current heap etc►  Faster startup >  No need to create initial state, config, … >  Used in V8 already for standard JavaScript libraries >  How long does a JVM need to start up?►  Possible answer to mobile applications killed due to memory constraints►  Could be used to migrate isolates between machines27.10.11 33

Dart Editor►  Editor for Dart applications►  Based on Eclipse►  Code in the Open Source Project27.10.11 34

More Complex Example►  Swarm: A newsreader►  Completely written in Dart >  App code: 3210 LOC >  UI library code: 13200 LOC >  Animation yields 30 fps >  Runs on iPad and Chrome27.10.11 35

Not Decided Yet…►  Currently a technology preview►  Some questions are open >  Reflection? Probably using Mirrors >  Changing classes on the fly? Probably not needed due to Isolates >  What about Chrome?27.10.11 36

Links►  http://www.dartlang.org/ >  Language Site >  Tutorials >  Language Spec >  Library Spec >  …►  http://dart.googlecode.com/ >  Open Source project >  Including compiler, VM etc.►  http://code.google.com/p/jdart/ >  Dart on the JVM►  http://it-republik.de/jaxenter/artikel/Google-Dart-4121.html >  German►  http://jonaswesterlund.se/dart.html >  Pre compiled Dart for Mac OS X►  http://www.infoq.com/articles/google-dart27.10.11 37

Possible Applications for Dart►  Google App Engine >  Isolates are a nice fit for GAE’s restriction >  Snapshot will make it easy to move execution from machine to machine►  Android >  As a replacement for Java►  Web Browser >  Compiling into JavaScript27.10.11 38

Dart: Conclusion – Huge Potential►  Best shot at next generation web language so far►  Language designed to appeal to the masses►  Solves a real problem: Complex web applications►  Already possible to create cross platform web applications►  Google has a lot of resources and this solves a real problem for them►  Isolates and future concurrency models very interesting >  Client: Security >  Server: Modern concurrency >  …27.10.11 39

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Google Dart

by Eberhard Wolff on Oct 13, 2011

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Google Dart — Presentation Transcript