Re: Map literal

[Alexander Jones]

I think you're overlooking the parse-time shape checking, Isiah, which in
the new world order of type inference and checking seems like a necessity
to me.

While I fully appreciate that Tab's solution involves the least number of
specification additions, I still would rather write this without the extra
pair of parens and the `new` which was omitted, just to cut down on the
noise and really reduce the number of reasons people have to use `Object`
instead of a more suitable type. Consider embedding lists as keys in a map
which compares keys by value:

```
let m =  new Dict(#(1: "one", new List(#(1, 2)): "array of 1 and 2", null:
"the null value"));
```

I think this just starts to look quite gnarly, and the fewer occurrences of
`new` I see in declarative code the better.

Re-consider my offered alternative, (putting `#{}` and `#[]` back on the
table to visually distinguish abstract list and abstract mapping):

```
let m =  Dict#{1: "one", List#[1, 2]: "array of 1 and 2", null: "the null
value"};

let platonics = Set#["tetrahedron", "cube", "octahedron", "dodecahedron",
"icosahedron"];
```

I think it would also make sense to allow `...` to include the results of
iteration over some other iterable.

```
let nums = [2, 3, 4];
let setOfNums = Set#[1, 2, 3, ...nums, ...range(20, 50)];
```

Cheers

On Sunday, 29 November 2015, Isiah Meadows  wrote:

> With that syntax, I'm not even sure it's necessary. It's not much more
> concise than a list of 2-tuples. Don't quite see the benefit the other than
> a few characters.
>
> On Sat, Nov 28, 2015, 22:22 Tab Atkins Jr.  wrote:
>
>> On Thu, Oct 29, 2015 at 6:23 PM, Alexander Jones  wrote:
>> > 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.)
>>
>> I strongly agree with a lot of the points here, and think they suggest
>> the OP's suggestion was generalized in slightly the wrong way.
>> Producing a Map literal is indeed too specific to justify syntax, but
>> what's suggested is not a special way of calling some constructors,
>> but *a literal syntax for 2-value iterators*.
>>
>> We have a literal syntax for 1-value iterators: just use an Array.
>> It's lightweight (2 chars + 1 char per item), and typos in the syntax
>> are caught at compile time.  Our existing literal syntax for 2-value
>> iterators (an array of length-2 arrays) fails at both of these: it's
>> heavyweight (4 chars + 4 chars per item), and typos in the syntax are
>> only caught at runtime, when it's actually iterated over.
>>
>> Having a lightweight, compile-time-checked 2-value 

Re: Map literal

[Isiah Meadows]

With that syntax, I'm not even sure it's necessary. It's not much more
concise than a list of 2-tuples. Don't quite see the benefit the other than
a few characters.

On Sat, Nov 28, 2015, 22:22 Tab Atkins Jr.  wrote:

> On Thu, Oct 29, 2015 at 6:23 PM, Alexander Jones  wrote:
> > 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.)
>
> I strongly agree with a lot of the points here, and think they suggest
> the OP's suggestion was generalized in slightly the wrong way.
> Producing a Map literal is indeed too specific to justify syntax, but
> what's suggested is not a special way of calling some constructors,
> but *a literal syntax for 2-value iterators*.
>
> We have a literal syntax for 1-value iterators: just use an Array.
> It's lightweight (2 chars + 1 char per item), and typos in the syntax
> are caught at compile time.  Our existing literal syntax for 2-value
> iterators (an array of length-2 arrays) fails at both of these: it's
> heavyweight (4 chars + 4 chars per item), and typos in the syntax are
> only caught at runtime, when it's actually iterated over.
>
> Having a lightweight, compile-time-checked 2-value iterator literal
> that desugars to an N×2 Array (or ArrayIterator) fixes all these
> problems, and makes it easy to write Map literals, Immutable.Dict
> literals, or anything else.  Using the hash-paren syntax suggested
> above:
>
> ```
> let m =  Map(#(1: "one", [1, 2]: "array of 1 and 2", null: "the null
> value"));
> ```
>
> There's no need to invent a new function-calling syntax or add a new
> well-known symbol to anything. It Just Works™ as long as the function
> you pass it to expects a 2-value iterator.
>
> (From other languages, there doesn't appear to be any call for N×3
> literals or anything higher
>
> ~TJ
>
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Re: Map literal

[Isiah Meadows]

I was actually talking about the syntax itself. I'd be fine with less
verbose, extensible Map semantics.

On Sun, Nov 29, 2015, 12:14 Alexander Jones  wrote:

> I think you're overlooking the parse-time shape checking, Isiah, which in
> the new world order of type inference and checking seems like a necessity
> to me.
>
> While I fully appreciate that Tab's solution involves the least number of
> specification additions, I still would rather write this without the extra
> pair of parens and the `new` which was omitted, just to cut down on the
> noise and really reduce the number of reasons people have to use `Object`
> instead of a more suitable type. Consider embedding lists as keys in a map
> which compares keys by value:
>
> ```
> let m =  new Dict(#(1: "one", new List(#(1, 2)): "array of 1 and 2", null:
> "the null value"));
> ```
>
> I think this just starts to look quite gnarly, and the fewer occurrences
> of `new` I see in declarative code the better.
>
> Re-consider my offered alternative, (putting `#{}` and `#[]` back on the
> table to visually distinguish abstract list and abstract mapping):
>
> ```
> let m =  Dict#{1: "one", List#[1, 2]: "array of 1 and 2", null: "the null
> value"};
>
> let platonics = Set#["tetrahedron", "cube", "octahedron", "dodecahedron",
> "icosahedron"];
> ```
>
> I think it would also make sense to allow `...` to include the results of
> iteration over some other iterable.
>
> ```
> let nums = [2, 3, 4];
> let setOfNums = Set#[1, 2, 3, ...nums, ...range(20, 50)];
> ```
>
> Cheers
>
>
> On Sunday, 29 November 2015, Isiah Meadows  wrote:
>
>> With that syntax, I'm not even sure it's necessary. It's not much more
>> concise than a list of 2-tuples. Don't quite see the benefit the other than
>> a few characters.
>>
>> On Sat, Nov 28, 2015, 22:22 Tab Atkins Jr.  wrote:
>>
>>> On Thu, Oct 29, 2015 at 6:23 PM, Alexander Jones  wrote:
>>> > 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.)
>>>
>>> I strongly agree with a lot of the points here, and think they suggest
>>> the OP's suggestion was generalized in slightly the wrong way.
>>> Producing a Map literal is indeed too specific to justify syntax, but
>>> what's suggested is not a special way of calling some constructors,
>>> but *a literal syntax for 2-value iterators*.
>>>
>>> We have a literal syntax for 1-value iterators: just use an Array.
>>> It's lightweight (2 chars + 1 char per item), and typos in the 

Re: Map literal

[Isiah Meadows]

I like the idea of the #{} syntax working without a required type. But
here's my opinions:

1. It should automatically [[Construct]]. I don't see any other reason why
it shouldn't.
2. I don't like the idea of an `->` operator which does that. Also, is `a
-> b -> c` equivalent to `[a,  b, c]` or `[a, [b, c]]`? I just don't like
it.
3. I can see why you want an untyped version to destructure into a list of
2-tuples, but I fear it would lead into the same pitfalls of the extreme
consistency in `this`. Every ES5 function has its own `this`, which led
people into problems when they forgot about it when using inner functions.
Forth is one of the simplest, most consistent languages out there (it's an
old concatenative, stack-based language, for those unfamiliar). But it's
easy to trip up if your stack has the wrong value, it leaves one too many
values on the stack, or you pass one too few values to it. And this fails
silently.

On Sun, Nov 29, 2015, 16:41 Francisco Tolmasky  wrote:

> My one desire (perhaps not completely substantiated) would be that the
> “list” portion of the syntax exist outside of these expressions as well.
> That is to say, if:
>
> ```
> new Dict#{a: b, c: d }
> ```
>
> desugars to:
>
> ```
> new Dict([[a,b], [c,d]])
> ```
>
> Then I’d like/expect #{a: b, c: d} to also just desugar to [[a,b], [c,d]].
> More than anything, I would just expect this to be the case if I ran into
> it in the wild. As such, perhaps one way to look at this is that what we
> actually want is a nice tuple syntax. Imagine if we had just a tuple syntax
> taht a->b desugars to [a,b]. Now, with no further changes, we get this “map
> syntax” for free:
>
> ```
> new Map([a->b, (4+5)->d, null->7])
> ```
>
> That looks pretty good to me, and introduces a new operator that behaves
> the same everywhere, and has minimal requirements to “new” collection
> classes. Additionally, I would enjoy returning these as well when referring
> to key value pairs:
>
> ```
> return (a->b) // sugar for return [a,b]
> ```
>
> --
> Francisco Tolmasky
> www.tolmasky.com
> tolma...@gmail.com
> ___
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> https://mail.mozilla.org/listinfo/es-discuss
>
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Re: Map literal

[Tab Atkins Jr.]

On Thu, Oct 29, 2015 at 6:23 PM, Alexander Jones  wrote:
> 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.)

I strongly agree with a lot of the points here, and think they suggest
the OP's suggestion was generalized in slightly the wrong way.
Producing a Map literal is indeed too specific to justify syntax, but
what's suggested is not a special way of calling some constructors,
but *a literal syntax for 2-value iterators*.

We have a literal syntax for 1-value iterators: just use an Array.
It's lightweight (2 chars + 1 char per item), and typos in the syntax
are caught at compile time.  Our existing literal syntax for 2-value
iterators (an array of length-2 arrays) fails at both of these: it's
heavyweight (4 chars + 4 chars per item), and typos in the syntax are
only caught at runtime, when it's actually iterated over.

Having a lightweight, compile-time-checked 2-value iterator literal
that desugars to an N×2 Array (or ArrayIterator) fixes all these
problems, and makes it easy to write Map literals, Immutable.Dict
literals, or anything else.  Using the hash-paren syntax suggested
above:

```
let m =  Map(#(1: "one", [1, 2]: "array of 1 and 2", null: "the null value"));
```

There's no need to invent a new function-calling syntax or add a new
well-known symbol to anything. It Just Works™ as long as the function
you pass it to expects a 2-value iterator.

(From other languages, there doesn't appear to be any call for N×3
literals or anything higher

~TJ
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Re: Map literal

[Isiah Meadows]

That's something no one here really thought of yet. I don't personally have
a lot of investment in this.

(@Alex and yes, much of that was based on your idea. It was a great
starting point.)

On Thu, Oct 29, 2015, 21:23 Alexander Jones  wrote:

> 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  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  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 
>>> 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 
 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 :

> 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 

Re: Map literal

[Isiah Meadows]

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  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  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  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 :
>>
>>> 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  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  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  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 

Re: Map literal

[Alexander Jones]

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  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  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 
>> 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  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 :
>>>
 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  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);

Re: Map literal

[Herby Vojčík]

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
> 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 >:

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
> 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 :

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.
 wrote:

On Wed, Oct 28, 2015 at 8:36 AM, Alexander Jones
 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.
 >
 

Re: Map literal

[Herby Vojčík]

Herby Vojčík wrote:

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.

... though the second feels more ...
___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Re: Map literal

[Alexander Jones]

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  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
>> > 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 > >:
>>
>> 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
>> > >
>> 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) 

Re: Map literal

[Alexander Jones]

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  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  > 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
>>> > 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 >> >:
>>>
>>> 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
>>> >> 

Re: Map literal

[Alexander Jones]

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 
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  >:
>
>> 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. > > wrote:
>>
>>> On Wed, Oct 28, 2015 at 8:36 AM, Alexander Jones  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
>>
>>
>
___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Re: Map literal

[Viktor Kronvall]

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 :

> 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 
> 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 :
>>
>>> 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. 
>>> wrote:
>>>
 On Wed, Oct 28, 2015 at 8:36 AM, Alexander Jones  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
>>>
>>>
>>
___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Re: Map literal

[Alexander Jones]

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 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 
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  >:
>
>> 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 > > 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 :
>>>
 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. 
 wrote:

> On Wed, Oct 28, 2015 at 8:36 AM, Alexander Jones 
> 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


>>>
>
___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Re: Map literal

[Michał Wadas]

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 :

> 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  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  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  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
> > 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 

Re: Map literal

[Mohsen Azimi]

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  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  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  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
 > 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 >:

 Hi Victor

 Not sure I 

Re: Map literal

[Dave Porter]

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  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  >:
> 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  > 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  > 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 > 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
>  >> 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 

Re: Map literal

[Alexander Jones]

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  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  > 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  >:
>
>> 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 > > 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 >> > 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  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 

Re: Map literal

[Viktor Kronvall]

> ```
> 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 :

> 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. 
> wrote:
>
>> On Wed, Oct 28, 2015 at 8:36 AM, Alexander Jones  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
>>
>
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Re: Map literal

[Alexander Jones]

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.

Rather, we have an opportunity to instead devise a syntax for an abstract
map. While we're at it, we might as well do the same for an abstract list.
Why should maps have all the fun?

```
const {List: IList, Map: IMap} = Immutable;
const bar = 43;
const map = IMap#{"foo": 42, bar: 44};  // keys "foo" and 43
const list = IList#[4, 5, 6, 7, Map#{map: "why not?"}];  // 5th element is
a Map with one key, which is the Immutable.Map above
const weakMap = WeakMap#{map: "It's an Immutable", list: "Also Immutable"};
 // WeakMap keys are the objects map and list
```

It could desugar as, for the sake of example:

```
Foo#{key: value, ...}
➔
Foo[Symbol.literalOf]([[key, value], ...][Symbol.iterator]())
```

and

```
Foo#[value, ...]
➔
Foo[Symbol.literalOf]([value, ...][Symbol.iterator]())
```

The nice thing about this is it's extensible and future proofs the language
a little bit. The actual arrays need not exist if engines choose to
implement this more efficiently - the syntax just results in an iterator
which yields the elements of the literal. The only difference between the
`[]` and the `{}` notation ise that the `{}` notation enforces
syntactically valid key-value pairs and are a little less heavy on brackets.

I know literally every proposal ever these days seems to claim the `#`
symbol now, so that's clearly an issue to contend with... :)

Alex


On 27 October 2015 at 22:55, Mohsen Azimi  wrote:

> I'm using Maps a lot now and I was thinking why there is no "easy" way of
> declaring them like objects and arrays.
>
> I'm sure I'm not the first one who came up with the idea of having Map
> literal declaration. There are many ways we can introduce new syntax for
> declaring Maps via a literal syntax such as:
>
> ```
> let map = [window: 'window', document: 'document'];
> ```
> or
> ```
> let map = {{window: 'window', document: 'document'}}
> ```
> and possibly many more.
>
> I searched the discussions  but couldn't find a topic on this. Have you
> discussed this before?
>
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> https://mail.mozilla.org/listinfo/es-discuss
>
>
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Re: Map literal

[Tab Atkins Jr.]

On Wed, Oct 28, 2015 at 8:36 AM, Alexander Jones  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
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Re: Map literal

[Jordan Harband]

fwiw, my Object.entries proposal (
https://github.com/ljharb/proposal-object-values-entries ) would allow you
to do: `new Map(Object.entries({ a: 'b', b: 'c' }))`.

On Tue, Oct 27, 2015 at 4:36 PM, Alexander Jones  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.
>
> Rather, we have an opportunity to instead devise a syntax for an abstract
> map. While we're at it, we might as well do the same for an abstract list.
> Why should maps have all the fun?
>
> ```
> const {List: IList, Map: IMap} = Immutable;
> const bar = 43;
> const map = IMap#{"foo": 42, bar: 44};  // keys "foo" and 43
> const list = IList#[4, 5, 6, 7, Map#{map: "why not?"}];  // 5th element is
> a Map with one key, which is the Immutable.Map above
> const weakMap = WeakMap#{map: "It's an Immutable", list: "Also
> Immutable"};  // WeakMap keys are the objects map and list
> ```
>
> It could desugar as, for the sake of example:
>
> ```
> Foo#{key: value, ...}
> ➔
> Foo[Symbol.literalOf]([[key, value], ...][Symbol.iterator]())
> ```
>
> and
>
> ```
> Foo#[value, ...]
> ➔
> Foo[Symbol.literalOf]([value, ...][Symbol.iterator]())
> ```
>
> The nice thing about this is it's extensible and future proofs the
> language a little bit. The actual arrays need not exist if engines choose
> to implement this more efficiently - the syntax just results in an iterator
> which yields the elements of the literal. The only difference between the
> `[]` and the `{}` notation ise that the `{}` notation enforces
> syntactically valid key-value pairs and are a little less heavy on brackets.
>
> I know literally every proposal ever these days seems to claim the `#`
> symbol now, so that's clearly an issue to contend with... :)
>
> Alex
>
>
> On 27 October 2015 at 22:55, Mohsen Azimi  wrote:
>
>> I'm using Maps a lot now and I was thinking why there is no "easy" way of
>> declaring them like objects and arrays.
>>
>> I'm sure I'm not the first one who came up with the idea of having Map
>> literal declaration. There are many ways we can introduce new syntax for
>> declaring Maps via a literal syntax such as:
>>
>> ```
>> let map = [window: 'window', document: 'document'];
>> ```
>> or
>> ```
>> let map = {{window: 'window', document: 'document'}}
>> ```
>> and possibly many more.
>>
>> I searched the discussions  but couldn't find a topic on this. Have you
>> discussed this before?
>>
>> ___
>> es-discuss mailing list
>> es-discuss@mozilla.org
>> https://mail.mozilla.org/listinfo/es-discuss
>>
>>
>
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>
>
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Re: Map literal

[Alexander Jones]

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.  wrote:

> On Wed, Oct 28, 2015 at 8:36 AM, Alexander Jones  > 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
>
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Re: Map literal

[Alexander Jones]

Quite verbose, harder to optimize and only supports string keys.

On Wednesday, 28 October 2015, Jordan Harband  wrote:

> fwiw, my Object.entries proposal (
> https://github.com/ljharb/proposal-object-values-entries ) would allow
> you to do: `new Map(Object.entries({ a: 'b', b: 'c' }))`.
>
> On Tue, Oct 27, 2015 at 4:36 PM, Alexander Jones  > 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.
>>
>> Rather, we have an opportunity to instead devise a syntax for an abstract
>> map. While we're at it, we might as well do the same for an abstract list.
>> Why should maps have all the fun?
>>
>> ```
>> const {List: IList, Map: IMap} = Immutable;
>> const bar = 43;
>> const map = IMap#{"foo": 42, bar: 44};  // keys "foo" and 43
>> const list = IList#[4, 5, 6, 7, Map#{map: "why not?"}];  // 5th element
>> is a Map with one key, which is the Immutable.Map above
>> const weakMap = WeakMap#{map: "It's an Immutable", list: "Also
>> Immutable"};  // WeakMap keys are the objects map and list
>> ```
>>
>> It could desugar as, for the sake of example:
>>
>> ```
>> Foo#{key: value, ...}
>> ➔
>> Foo[Symbol.literalOf]([[key, value], ...][Symbol.iterator]())
>> ```
>>
>> and
>>
>> ```
>> Foo#[value, ...]
>> ➔
>> Foo[Symbol.literalOf]([value, ...][Symbol.iterator]())
>> ```
>>
>> The nice thing about this is it's extensible and future proofs the
>> language a little bit. The actual arrays need not exist if engines choose
>> to implement this more efficiently - the syntax just results in an iterator
>> which yields the elements of the literal. The only difference between the
>> `[]` and the `{}` notation ise that the `{}` notation enforces
>> syntactically valid key-value pairs and are a little less heavy on brackets.
>>
>> I know literally every proposal ever these days seems to claim the `#`
>> symbol now, so that's clearly an issue to contend with... :)
>>
>> Alex
>>
>>
>> On 27 October 2015 at 22:55, Mohsen Azimi > > wrote:
>>
>>> I'm using Maps a lot now and I was thinking why there is no "easy" way
>>> of declaring them like objects and arrays.
>>>
>>> I'm sure I'm not the first one who came up with the idea of having Map
>>> literal declaration. There are many ways we can introduce new syntax for
>>> declaring Maps via a literal syntax such as:
>>>
>>> ```
>>> let map = [window: 'window', document: 'document'];
>>> ```
>>> or
>>> ```
>>> let map = {{window: 'window', document: 'document'}}
>>> ```
>>> and possibly many more.
>>>
>>> I searched the discussions  but couldn't find a topic on this. Have you
>>> discussed this before?
>>>
>>> ___
>>> es-discuss mailing list
>>> es-discuss@mozilla.org
>>> 
>>> https://mail.mozilla.org/listinfo/es-discuss
>>>
>>>
>>
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>> es-discuss@mozilla.org
>> 
>> https://mail.mozilla.org/listinfo/es-discuss
>>
>>
>
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