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 <isiahmead...@gmail.com> 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. <jackalm...@gmail.com> wrote:
>
>> On Thu, Oct 29, 2015 at 6:23 PM, Alexander Jones <a...@weej.com> 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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