Map: filter/map and more

[Axel Rauschmayer]

> At the meeting it was decided not to go with `map` and `filter` sitting on `Map.prototype`, but instead to use iterators in the way like:
> 
> ```
> map
>   .entries() // returns an iterator
>   .map((v, k, m) => { ... })
>   .filter((v, k, m) => { ... })
>   .collect(); // returns a new map after all transforms
> ```

Convenient, but this pattern couldn’t be extended to new Map classes or other collections. I see two alternatives.

First, use the `Map` constructor. I don’t find this too bad and it’s self-explanatory.

```js
new Map(map
  .entries() // returns an iterator
  .map((v, k, m) => { ... })
  .filter((v, k, m) => { ... }));
```

Second:

```js
map
  .entries() // returns an iterator
  .map((v, k, m) => { ... })
  .filter((v, k, m) => { ... })
  .collectInto(new Map());
```

`collectInto(coll)` invokes `coll.set(k,v)` for each pair `[k,v]` in the sequence. It returns `coll`.

-- 
Dr. Axel Rauschmayer
axel at rauschma.de
rauschma.de



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