On Wed, Oct 1, 2014 at 11:57 AM, Rick Waldron <[email protected]> wrote:
> > > On Wed, Oct 1, 2014 at 2:50 PM, Dmitry Soshnikov < > [email protected]> wrote: > >> Hi, >> >> (Maps are awesome!) >> >> 1. Transforming iteration methods >> >> We're currently polyfillying the `Map`, and got some questions form devs. >> One of them is about transforming iteration methods, like `map` and >> `filter`. >> >> Unfortunately I missed that part of the spec when it was approved, so can >> someone please remind/clarify -- was it an intended decision not to hap >> Map#map, Map#filter? I can see only Map#forEach in the spec. Are maps >> "immutable"? -- That's fine, the `map` and `filter` return a new map. >> > > > Only with regard to time. I expect there will be substantial additions to > Map and Set in ES7 (as long as the work is done, of course). > Hm, sounds like two copy-pasting algorithms from the same `Array#map`, `Array#filter`, or just tweaking the `Map#forEach` (I might be missing something). > > >> >> 2. Declarative syntax >> >> The other thing to note: currently maps a lack of a nice declarative >> syntax. This one came from the use-case for maps for dynamic (computed) >> property names. >> > >> Previously, we had to allocate an empty object, and then, in the >> imperative style, append needed props: >> >> ``` >> var requestData = {}; >> requestData[Names.ID] = id; >> requestData[Names.EMAIL] = email; >> requestData.needsReload = true; >> ... >> new Request(...) >> .setData(requestData) >> .send(); >> ``` >> >> With computed properties of object initialisers it's much simpler and >> convenient: >> >> ``` >> new Request(...) >> .setData({ >> [Names.ID]: id, >> [Names.EMAIL]: email, >> needsReload: true, >> }) >> .send(); >> ``` >> >> Then thing is: if we'd like to use maps for such use-case, it brings us >> back to that inconvenient imperative style of assignments (even worse, >> since you have to repeat that `.set(...)` constantly): >> >> ``` >> var requestData = new Map(); >> requestData.set(Names.ID, id); >> requestData.set(Names.EMAIL, email); >> requestData.set('needsReload', id); >> ... >> ``` >> >> Yes, we provide the iterable option for the constructor, and it can be >> rewritten as (and this can even be inlined): >> >> ``` >> var requestData = new Map([ >> [Names.ID, id], >> [Names.EMAIL, email], >> ['needsReload', id] >> ]); >> ``` >> >> However, obviously, it's too many arrays allocation for such a simple use >> case. >> >> Will it make sense having a nice declarative syntax like: >> >> ``` >> new Map({ >> [Names.ID]: id, >> [Names.EMAIL]: email, >> needsReload: true, >> }) >> ``` >> > > This doesn't work because Maps allow objects as keys. > > Yes, I said it myself above. That's the thing -- I'd like to thing about some special syntax maybe. Don't know yet, probably map as a construct for declarative cases like: ``` // Declarative Map { [foo]: 1, bar: 2, } // Imperative (via constructor) new Map([ // brrr.. [foo, 1], ['bar', 2] ]) ``` Dmitry
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