I don't think borrowing object notation is a good idea. What exactly does
```
const myMap = Map#{
get foo() { return 100; },
set foo(v) {}
constructor() {}
};
```
mean?
Honestly, a very significant portion of the use cases I have for *actual
maps* don't involve string keys. So to borrow object notation and have to
constantly write keys in [] is pretty naff:
```
const describe = Dict#{
[1]: "one",
[[1, 2]]: "array of 1 and 2",
[null]: "the null value",
}; // please no!
```
If it makes people feel too weird to have comma separated, colon split
key-value pairs within curlies that *don't* parse like POJSOs, we could
have completely non-ambiguous parse with normal parentheses, I think?
```
const describe = Dict#(
1: "one",
[1, 2]: "array of 1 and 2",
null: "the null value",
);
```
That might limit confusion while giving a syntactically clean way to define
maps. Let's consider that a future mapping type like Dict compares
non-primitive keys by abstract value instead of by reference identity.
There are *tonnes* of nice use cases that open up that are taken for
granted in other languages and other classes like Immutable.Map - we're not
there yet with ES6 built-ins, so perhaps people might not yet appreciate
the value of this.
To reiterate a previous point, object property access with a statically
defined string key is idiomatically written `obj.foo`, so it makes sense
for symmetry to have `foo` appear as a bareword in a literal defining `obj
= {foo: 42}`. For most mapping-type classes this symmetry simply does not
apply, and frankly neither should it.
Also, I specifically suggested that the consumed value is an ArrayIterator
rather than an Array, because I feel having an intermediate Array around is
placing too high an importance on the humble Array. If the implementation
really wants an Array to work on internally, they can simply call
`Array.from` with little cost. But if they want an Immutable.List they can
have that instead without ever seeing an actual Array. (The Symbol.fromHash
method is just Symbol.literalOf as I called it - same thing, modulo
bikeshed.)
Alex
On 29 October 2015 at 22:51, Isiah Meadows <isiahmead...@gmail.com> wrote:
> Why not make it desugar to a direct function call with a single array of
> pairs? It's so parsed as a regular object, so shorthands can still be used.
>
> `Map#{foo: 1, bar: 2, 3: "baz"}`
> `Map[Symbol.fromHash]([[foo", 1], ["bar", 2], ["3", "baz]])`
>
> `Object#{foo: 1, bar: 2, 3: "baz"}`
> `Object[Symbol.fromHash]([[foo", 1], ["bar", 2], ["3", "baz]])`
>
> `Object.null#{foo: 1, bar: 2, 3: "baz"}`
> `Object.null[Symbol.fromHash]([[foo", 1], ["bar", 2], ["3", "baz]])`
>
> (`bar` doesn't have [[Construct]])
> `Object#{foo, bar() {}}`
> `Object[Symbol.fromHash]([[foo", foo], ["bar", function () {}]])`
>
> And as for implementation, use this:
>
> ```js
> extend class Map {
> static [Symbol.fromHash](pairs) {
> return new this(pairs);
> }
> }
>
> // etc...
>
> function SetKeys(target, pairs) {
> for (const [key, value] of pairs) {
> target[key] = value
> }
> return target
> }
>
> extend class Object {
> static [Symbol.fromHash](pairs) {
> return SetKeys({}, pairs)
> }
>
> static null(pairs) {
> return SetKeys(Object.create(null), pairs)
> }
> }
> ```
>
> Pretty simple IMHO. A helper decorator could even be made.
>
> On Wed, Oct 28, 2015, 14:34 Alexander Jones <a...@weej.com> wrote:
>
>> Also I would like to reiterate that errors in the shape of the N-by-2
>> array are only caught at runtime. That's really not ideal.
>>
>> On Wednesday, 28 October 2015, Dave Porter <david_por...@apple.com>
>> wrote:
>>
>>> I don’t love any of the specific suggestions so far, but saving 3 + 2n
>>> keystrokes isn't the point – readability and learnability are. Visually,
>>> `new Map([[‘foo’, 42]])` is a mess.
>>>
>>> On Oct 28, 2015, at 9:28 AM, Michał Wadas <michalwa...@gmail.com> wrote:
>>>
>>> Difference between any proposed here syntax and current state ( new
>>> Map([ [1,2], [2,3] ]); ) is..
>>>
>>> 3 characters + 2 characters/entry.
>>>
>>>
>>>
>>>
>>> 2015-10-28 17:22 GMT+01:00 Mohsen Azimi <m...@azimi.me>:
>>>
>>>> When I look at `Map#{"foo": 42}` I don't see much difference with `new
>>>> Map([['foo', 42]])`.
>>>>
>>>> Since you can pass expressions there, it's already possible to do it
>>>> with current syntax. There is only a bunch of extra brackets(`[` and `]`)
>>>> that I don't like.
>>>>
>>>>
>>>> On Wed, Oct 28, 2015 at 5:51 AM Alexander Jones <a...@weej.com> wrote:
>>>>
>>>>> Ah, there is actually a good case for keeping barewords in object
>>>>> literals but removing them from map literals, and that's due to objects
>>>>> accessing string properties as bare words, too. This is almost never the
>>>>> case for other map types.
>>>>>
>>>>> ```
>>>>> const o = {foo: 42};
>>>>> o.foo === 42;
>>>>> o.bar = 43;
>>>>>
>>>>> const m = Map#{"foo": 42};
>>>>> m.get("foo") === 42;
>>>>> m.set("bar", 43);
>>>>> ```
>>>>>
>>>>> Would you agree?
>>>>>
>>>>>
>>>>> On Wednesday, 28 October 2015, Alexander Jones <a...@weej.com> wrote:
>>>>>
>>>>>> Hi Herby
>>>>>>
>>>>>> Agree with your concerns about symmetry with object literals, but
>>>>>> many of the uses of maps benefit from having non string keys, and in such
>>>>>> case generally everything would involve wrapping in []. Trying to use an
>>>>>> Array as a key would be quite ugly with the extra squares required
>>>>>>
>>>>>> ```
>>>>>> const precachedResults = MyMap#{[[1, 2, 3]]: [1, 4, 9]}
>>>>>> vs
>>>>>> const precachedResults = MyMap#{[1, 2, 3]: [1, 4, 9]}
>>>>>> ```
>>>>>>
>>>>>> Perhaps a middle ground could be that if you want to use an
>>>>>> expression that would otherwise be a bare word, you enclose in parens.
>>>>>> The
>>>>>> visual binding of the colon is deceptive anyway, so I tend to do this if
>>>>>> the key expression contains a space:
>>>>>>
>>>>>> ```
>>>>>> MyMap#{1 + 2 + 3: 6}
>>>>>> vs.
>>>>>> MyMap#{(1 + 2 + 3): 6}
>>>>>> ```
>>>>>>
>>>>>> But I think I still prefer that the parsing for the key part is just
>>>>>> standard expression evaluation, personally, and the POJSO literal
>>>>>> barewords
>>>>>> remain the only special case.
>>>>>>
>>>>>> Indeed,
>>>>>>
>>>>>> ```
>>>>>> Object#{1: "one", Symbol(): "sym"}
>>>>>> ```
>>>>>>
>>>>>> Could Object-key-ify the keys, i.e. turn them into strings if not
>>>>>> symbols, and Just Work (but a default implementation on the Object
>>>>>> prototype is questionable!). That said I'm not sure we should be using
>>>>>> Object for this kind of thing. At this point I don't know what a raw
>>>>>> `#{}` should produce... There may be a better use case for it in the
>>>>>> future, horrible ASI complexities notwithstanding.
>>>>>>
>>>>>> Alex
>>>>>>
>>>>>>
>>>>>> On Wednesday, 28 October 2015, Herby Vojčík <he...@mailbox.sk> wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Alexander Jones wrote:
>>>>>>>
>>>>>>>> Ok, thanks for clarifying. Not only does it preserve order but it
>>>>>>>> also
>>>>>>>> permits non-string keys. You're still missing one detail which is
>>>>>>>> that
>>>>>>>> `bar` would actually be a variable not a string key.
>>>>>>>>
>>>>>>>> Another example to clarify that the key part would be an expression:
>>>>>>>>
>>>>>>>> ```
>>>>>>>> Map#{foo(42) + 7: "bar"}
>>>>>>>> ```
>>>>>>>>
>>>>>>>> I prefer this over the precedent set by object literals which would
>>>>>>>> require that [] are used around a key expression ("computed key")
>>>>>>>> simply
>>>>>>>>
>>>>>>>
>>>>>>> I, on the other hand, think it should match object literals
>>>>>>> completely. So your example would be
>>>>>>>
>>>>>>> ```
>>>>>>> Map#{[foo(42)+7]: "bar"}
>>>>>>> ```
>>>>>>>
>>>>>>> Yes, it's just for consistency and less WTF moment while learning
>>>>>>> the details.
>>>>>>>
>>>>>>> OTOH, there could be consistent contraproposal of:
>>>>>>>
>>>>>>> ```
>>>>>>> Object#{foo(42) + 7: "bar"}
>>>>>>> null#{foo(42) + 7: "bar"}
>>>>>>> #{foo(42) + 7: "bar"}
>>>>>>> ```
>>>>>>>
>>>>>>> where the first is equivalent to {[foo(42)+7]: "bar"}, the second is
>>>>>>> pure container (Object.create(null)) filled with properties, and the
>>>>>>> third
>>>>>>> is the default case, but I don't know which of the previous two - the
>>>>>>> first
>>>>>>> is probably less confusing, though the feels more clean.
>>>>>>>
>>>>>>> due to relieving the syntax noise, which is what this idea is all
>>>>>>>> about.
>>>>>>>> Also, this is how it works in Python and I make no apologies about
>>>>>>>> the
>>>>>>>> similarities ;)
>>>>>>>>
>>>>>>>> Alex
>>>>>>>>
>>>>>>>> On Wednesday, 28 October 2015, Viktor Kronvall
>>>>>>>> <viktor.kronv...@gmail.com <mailto:viktor.kronv...@gmail.com>>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>> Hello Alexander,
>>>>>>>>
>>>>>>>> I see now that I misread your desugaring.
>>>>>>>>
>>>>>>>> I read:
>>>>>>>>
>>>>>>>> ```
>>>>>>>> Map#{1: 6, bar: 'Hello', 2: 8};
>>>>>>>> ```
>>>>>>>> as being desugared to:
>>>>>>>>
>>>>>>>> ```
>>>>>>>> Map[Symbol.literalOf]({1: 6, bar: 'Hello', 2:
>>>>>>>> 8}[Symbol.iterator]());
>>>>>>>> ```
>>>>>>>>
>>>>>>>> But your proposal clearly states that is should be:
>>>>>>>>
>>>>>>>> ```
>>>>>>>> Map[Symbol.literalOf]([[1, 6], ['bar', 'Hello'],
>>>>>>>> [2,8]][Symbol.iterator]());
>>>>>>>> ```
>>>>>>>>
>>>>>>>> Which would preserve lexical ordering of entries. The fault is
>>>>>>>> completely mine. Sorry.
>>>>>>>>
>>>>>>>> I like this proposal as it is extensible and not that noisy in
>>>>>>>> syntax. Using the `#` for this doesn't
>>>>>>>> seem like a bad idea either. People coming from Erlang will be
>>>>>>>> familiar with this as well.
>>>>>>>>
>>>>>>>>
>>>>>>>> 2015-10-28 10:53 GMT+01:00 Alexander Jones <a...@weej.com
>>>>>>>> <javascript:_e(%7B%7D,'cvml','a...@weej.com');>>:
>>>>>>>>
>>>>>>>> Hi Victor
>>>>>>>>
>>>>>>>> Not sure I understand - the desugaring I wrote would
>>>>>>>> absolutely
>>>>>>>> preserve the written ordering because it speaks in terms of
>>>>>>>> an
>>>>>>>> ArrayIterator of key-value pairs. If the map type to which
>>>>>>>> it's
>>>>>>>> applied chooses to forget the ordering then that's fine.
>>>>>>>>
>>>>>>>> Alex
>>>>>>>>
>>>>>>>>
>>>>>>>> On Wednesday, 28 October 2015, Viktor Kronvall
>>>>>>>> <viktor.kronv...@gmail.com
>>>>>>>> <javascript:_e(%7B%7D,'cvml','viktor.kronv...@gmail.com');>>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>> > ```
>>>>>>>> > const map = IMap#{"foo": 42, bar: 44};
>>>>>>>> > ```
>>>>>>>> > It could desugar as, for the sake of example:
>>>>>>>> >
>>>>>>>> > ```
>>>>>>>> > Foo#{key: value, ...}
>>>>>>>> > ➔
>>>>>>>> > Foo[Symbol.literalOf]([[key, value],
>>>>>>>> ...][Symbol.iterator]())
>>>>>>>> > ```
>>>>>>>>
>>>>>>>> I like this proposal. However, Maps should guarantee
>>>>>>>> insertion order when traversing the keys and values and
>>>>>>>> desugaring it like that does not respect this guarantee
>>>>>>>> or
>>>>>>>> more precisely it will lead to (in my opinion)
>>>>>>>> unexpected
>>>>>>>> order of the keys.
>>>>>>>>
>>>>>>>> ```
>>>>>>>> Object.keys({1: 6, bar: 'Hello', 2: 8}); // → [ '1',
>>>>>>>> '2',
>>>>>>>> 'bar' ]
>>>>>>>> ```
>>>>>>>>
>>>>>>>> If I'm not mistaken this will be same order for `{1: 6,
>>>>>>>> bar:
>>>>>>>> 'Hello', 2: 8}[Symbol.iterator]()`.
>>>>>>>>
>>>>>>>> This implies that:
>>>>>>>>
>>>>>>>> ```
>>>>>>>> Map#{1: 6, bar: 'Hello', 2: 8};
>>>>>>>> ```
>>>>>>>>
>>>>>>>> Will not have entries in the order `[[1, 6], ['bar',
>>>>>>>> 'Hello'], [2,8]]` but instead `[[1,6], [2,8],
>>>>>>>> ['bar','Hello']]`.
>>>>>>>>
>>>>>>>> This means that possible future destructuring of a Map
>>>>>>>> will
>>>>>>>> be harder to reason about.
>>>>>>>>
>>>>>>>>
>>>>>>>> 2015-10-28 2:21 GMT+01:00 Alexander Jones <
>>>>>>>> a...@weej.com>:
>>>>>>>>
>>>>>>>> True, but easy to mess up and only be treated to a
>>>>>>>> runtime error. Three nested brackets at the start
>>>>>>>> and
>>>>>>>> end could definitely be better, and this just
>>>>>>>> encourages
>>>>>>>> people to use POJSOs instead. Also not a very
>>>>>>>> uniform
>>>>>>>> interface if you look at how to construct a Map,
>>>>>>>> Set or
>>>>>>>> Immutable.List at present, though admittedly
>>>>>>>> constructor
>>>>>>>> call for the ES6 types would be a partial
>>>>>>>> improvement.
>>>>>>>>
>>>>>>>> On Wednesday, 28 October 2015, Tab Atkins Jr.
>>>>>>>> <jackalm...@gmail.com> wrote:
>>>>>>>>
>>>>>>>> On Wed, Oct 28, 2015 at 8:36 AM, Alexander Jones
>>>>>>>> <a...@weej.com> wrote:
>>>>>>>> > I agree this is pretty important. Using
>>>>>>>> actual
>>>>>>>> maps really frees up a lot of
>>>>>>>> > complexity, but the syntax is cumbersome to
>>>>>>>> say
>>>>>>>> the least.
>>>>>>>> >
>>>>>>>> > Whatever the decided syntax, bare words as
>>>>>>>> string
>>>>>>>> keys is a really bad idea
>>>>>>>> > IMO. The key syntax should be parsed as an
>>>>>>>> expression, like the values are,
>>>>>>>> > and like they are in basically every other
>>>>>>>> language.
>>>>>>>> >
>>>>>>>> > Another outstanding issue is that we might
>>>>>>>> want
>>>>>>>> the syntax for
>>>>>>>> > `Immutable.Map`, or `WeakMap`, or
>>>>>>>> `MapTwoPointOh`
>>>>>>>> that improves deficiency
>>>>>>>> > $x, $y and $z. I'd say introducing a special
>>>>>>>> syntax for `Map` right now is
>>>>>>>> > not ideal.
>>>>>>>>
>>>>>>>> Currently, the "extensible literal syntax" for
>>>>>>>> this
>>>>>>>> isn't that bad:
>>>>>>>>
>>>>>>>> const bar = 43;
>>>>>>>> const map = Immutable.Map([["foo", 42], [bar,
>>>>>>>> 44]]);
>>>>>>>>
>>>>>>>> It's a little more verbose because the entries
>>>>>>>> have
>>>>>>>> to be surrounded
>>>>>>>> by [], but hey.
>>>>>>>>
>>>>>>>> ~TJ
>>>>>>>>
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> es-discuss mailing list
>>>>>>>> es-discuss@mozilla.org
>>>>>>>> https://mail.mozilla.org/listinfo/es-discuss
>>>>>>>>
>>>>>>>>
>>>>>>>>
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