Re: Set.prototype.entries: indices as keys?

[Brendan Eich]

Dmitry Soshnikov wrote:


```js
let [x,y] = set; // x='a'; y='b’;
```


Would this work actually? :) Destructuring does get property, which 
wouldn't call set's `get` method.


See 
http://people.mozilla.org/~jorendorff/es6-draft.html#sec-runtime-semantics-destructuringassignmentevaluation 
-- destructuring array patterns uses the iteration protocol, which is 
why the line works as Axel suggested:


js let set = new Set(['a', 'b']);
js let [x,y] = set;
js console.log(x, y)
a b
js for (let elt of set) console.log(elt)
a
b

But not all iterables are indexable, nor should they be.

/be
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Re: Set.prototype.entries: indices as keys?

[Axel Rauschmayer]

 Sets are not a linear data structure, so the order of entries in a Set is 
 irrelevant, unlike an Array whose elements must have an explicit position. 
 Set entries in JS have an iteration order purely to match programmer 
 intuition (and ensure that all implementations adhere), however there is no 
 structural importance of the order. 

You can impose an order on the elements of a set, though. For example, Java’s 
`SortedSet` [1] has the methods `first()` and `last()`, which are occasionally 
useful. I agree that it feels weird to have indices attached to set elements, 
but it would at least make `entries()` useful. You could iterate and treat the 
first element and/or the last element differently. But the same can be achieved 
by iterating over a `zip()` of a set and a `range()` (assuming iterable-based 
tool functions `zip` and `range`).

[1] http://docs.oracle.com/javase/7/docs/api/java/util/SortedSet.html

-- 
Dr. Axel Rauschmayer
a...@rauschma.de
rauschma.de

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Set.prototype.entries: indices as keys?

[Axel Rauschmayer]

Currently the keys of the entries returned by `Set.prototype.entries()` are the 
same as the values:

```js
let set = new Set(['a', 'b']);

let pairs = [...set.entries()];
console.log(JSON.stringify(pairs)); // [[a,a],[b,b”]]
```

Given that sets are ordered, I’d use the “position” of an entry as the key: 
[[0,a],[1,b”]]

Rationale: First, having an indices as keys makes the entries more useful. 
Second, destructuring already treats entries as if they had indices:

```js
let [x,y] = set; // x='a'; y='b’;
```

-- 
Dr. Axel Rauschmayer
a...@rauschma.de
rauschma.de



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Re: Set.prototype.entries: indices as keys?

[Mark Volkmann]

+1

---
R. Mark Volkmann
Object Computing, Inc.

 On Jan 18, 2015, at 6:28 AM, Axel Rauschmayer a...@rauschma.de wrote:
 
 Currently the keys of the entries returned by `Set.prototype.entries()` are 
 the same as the values:
 
 ```js
 let set = new Set(['a', 'b']);
 
 let pairs = [...set.entries()];
 console.log(JSON.stringify(pairs)); // [[a,a],[b,b”]]
 ```
 
 Given that sets are ordered, I’d use the “position” of an entry as the key: 
 [[0,a],[1,b”]]
 
 Rationale: First, having an indices as keys makes the entries more useful. 
 Second, destructuring already treats entries as if they had indices:
 
 ```js
 let [x,y] = set; // x='a'; y='b’;
 ```
 
 -- 
 Dr. Axel Rauschmayer
 a...@rauschma.de
 rauschma.de
 
 
 
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