Iterators & Generators in ECMAScript 6.0

1. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com

2. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
foreach (object obj in list) {
DoSomething(obj);
}
Enumerator e = list.GetEnumerator();
while (e.MoveNext()) {
object obj = e.Current;
DoSomething(obj);
}
public interface IEnumerable{
IEnumerator GetEnumerator();
}
public interface IEnumerator{
object Current {get;}
bool MoveNext();
void Reset();
}

3. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
class Range{
constructor(low, high){ this.low = low; this.high = high; }
[Symbol.iterator](){
return new RangeIterator(this);
}
}
class RangeIterator{
constructor(range){ this.range = Range; this.current = this.range.low; }
next(){
if( this.current > this.range.high ){
return { value : undefined, done : true };
} else {
return { value : this.current++, done : false };
}
}
}
for( let i of new Range(1, 3) ) { console.log(i); }
// Like IEnumerable in C#
// Like IEnumerator in C#
// Like foreach in C#

4. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var colors = new Set(['rojo', 'amarillo', 'azul']);
for (let word of colors){
alert(word); // "rojo", "amarillo", "azul" (the data)
}

5. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
let arr = [ "blue", "green" ];
arr.notAnIndex = 123;
Array.prototype.protoProp = 456;
for (let k in arr) {
console.log(k);
}
Print:
> 0
> 1
> notAnIndex
> protoProp

6. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com

7. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
public class Test {
public IEnumerator GetEnumerator() {
yield return "Hello";
yield return "World";
}
}

8. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
public class Test {
public IEnumerator GetEnumerator() {
return new __Enumerator(this);
}
} private class __Enumerator : IEnumerator{
object current;
int state;
public bool MoveNext() {
switch (state) {
case 0:
current = "Hello";
state = 1;
return true;
case 1:
current = "World";
state = 2;
return true;
default:
return false;
}
}
public object Current { get { return current; } }
}

9. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
function *simpleGenerator(){
yield "Hello";
yield "World";
for (var i = 0; i < 2; i++)
yield i;
}
var g = simpleGenerator();
print(g.next()); // "Hello"
print(g.next()); // "World"
print(g.next()); // 0
print(g.next()); // 1

10. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
class Range{
constructor(low, high){
this.low = low;
this.high = high;
}
*[Symbol.iterator](){
for (let i = this.low; i <= this.high; i++) {
yield i;
}
}
}
for (var i in new Range(3, 5) ) {
print(i); // 3, 4, 5 in sequence
}
// Like IEnumerable in C#

11. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
function* g1() { yield 2; yield 3; }
function* g2() {
yield 1;
yield* g1();
yield 4;
}
var iterator = g2();
console.log( iterator.next().value ); // 1
console.log( iterator.next().value ); // 2
console.log( iterator.next().value ); // 3
console.log( iterator.next().value ); // 4

12. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
function* longRunningTask() {
let result1 = yield* step1();
yield;
let result2 = yield* step2();
yield;
yield* step3(result1, result2);
}
function* step1() { ... return result1; }
function* step2() { ... return result2; }
function* step3(p1, p2) { ... }

13. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
function* fibonacci() {
let [prev, curr] = [0, 1];
for (;;) {
[prev, curr] = [curr, prev + curr];
yield curr;
}
}
for (n of fibonacci()) {
// truncate the sequence at 1000
if (n > 1000)
break;
print(n);
}

14. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
link
let items = [1, 2, 3, 4, 5, 6]
.asEnumerable()
.where(x => x % 2)
.select(x => x + 1);
for (let item in items) {
console.log(item);
}
//output will be 2, 4, 6

15. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
http://www.2ality.com/
Understanding ECMAScript 6
http://ecmascript6.org/
A Few New Things Coming To JavaScript
HARMONY OF DREAMS COME TRUE
Harmony specification_drafts

16. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
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