CS2 Discussion: Features: Support splats in object literals (object rest/spread syntax)

[connec]

I would love to see object spreads and rests supported via splats in object literals:

{ foo, rest... } = { foo: 1, bar: 2 }
console.log foo, rest # 1 { bar: 2 }
console.log { foo, rest... } # { foo: 1, bar: 2 }

obj = { foo: 1 }
copy = { ...obj }
console.log obj === copy # false

setName = (name, record) -> { name, record... }
console.log setName 'greeting', hello: 'world' # { name: 'greeting', hello: 'world' }

stripName = ({ name, record... }) -> record
console.log stripName name: 'greeting', hello: 'world' # { hello: 'world' }

Compilation in the 2 branch could happily use Object.assign for construction:

// console.log { foo, rest... }
console.log(Object.assign({ foo }, rest))

Destructuring would require more implementation, e.g.

// { foo, rest... } = { foo: 1, bar: 2 }
var ref, ref1, ref2, i, k, foo, rest
ref = { foo: 1, bar: 2 }
ref1 = Object.keys(ref)
ref2 = [ 'foo' ] // compiler-generated list of the non-splat properties
foo = ref.foo
rest = {}
for (i = 0; i < ref1.length; i++) {
  k = ref1[i]
  if (ref2.indexOf(k) < 0) {
    rest[k] = ref[k]
  }
}

We could alternatively wait for the proposal to land in environments, or rely on a transpiler like babel.

[JavascriptIsMagic]

I've been seeing object spread being recommended and I've seen it being used heavily in large production code bases. I find myself using Object.assign quite a bit myself in situations where I would have much cleaner code using object spread, and it is such a nice compliment to the array... spread

---

I think this does require you to use the {brackets} in the syntax or it will get ambiguous with the array... spread:

fun a: 1, b...   # ambiguous
fun {a: 1, b...} # unambiguous

---

Also do we go with the spec and put the operator on the left { ...spread } or go with coffeescripty { spread... } ?

One benefit to having it go in the opposite direction would be that it could disambiguate the two and we could get rid of the need for {brackets}

# object spread:
fun a: 1, ...b # fun({ a: 1, ...b })
# argument spread:
fun a: 1, b... # fun({ a: 1 }, ...b)

Though consistency of the spread syntax might be preferred over getting rid of ambiguity.

[connec]

I'd definitely vote for consistency over that ambiguity, though it is an annoying one. Ultimately I suppose it's consistent with needing explicit braces to have shorthand objects in arguments lists too.

f a: a, b     # f({ a: a }, b)
f { a: a, b } # f({ a: a, b: b })

[YamiOdymel]

I'd recommend to put the ... in front of the object, variable,

so you can spread an object from the function like this (This is very common in Vuex, Redux):

export default {
    name: 'CounterBlock'
    methods:
        ...mapActions
            increment : counter.actions.increment,
            set       : counter.actions.set,
            fetchCount: counter.actions.fetchCount
    computed:
        ...mapGetters
            total: counter.getters.total
}

currently with coffeescript@2.0.0-alpha1 there's no spread operator, so you would have to use Object.assign({}, obj1, obj2) instead.

export default {
    name: 'CounterBlock'
    methods: Object.assign {}, mapActions
            increment : counter.actions.increment,
            set       : counter.actions.set,
            fetchCount: counter.actions.fetchCount
    computed: Object.assign {}, mapGetters
            total: counter.getters.total
}

with ECMAScript6

export default {
    name: 'CounterBlock',
    methods: {
        ...mapActions({
            increment : counter.actions.increment,
            set       : counter.actions.set,
            fetchCount: counter.actions.fetchCount
        })
    },
    computed: {
        ...mapGetters ({
            total: counter.getters.total
        })
    },
}

[GeoffreyBooth]

Added via jashkenas/coffeescript#4493

[c5n8]

@GeoffreyBooth @YamiOdymel
After #4493, how can we get below code now?

...mapActions({
  increment : counter.actions.increment,
  set       : counter.actions.set,
  fetchCount: counter.actions.fetchCount
})

[YamiOdymel]

@chabib Well, if I'm not mistaken, you could use it like this.

object = {
    ...mapActions
        increment : counter.actions.increment,
        set       : counter.actions.set,
        fetchCount: counter.actions.fetchCount
}

Which produces:

var object, _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; };

object = _extends({}, mapActions({
      increment: counter.actions.increment,
      set: counter.actions.set,
      fetchCount: counter.actions.fetchCount
}));

is the same as below with ECMAScript6

object = {
    ...mapActions({
        increment : counter.actions.increment,
        set       : counter.actions.set,
        fetchCount: counter.actions.fetchCount
    })
}

[c5n8]

Thank you @YamiOdymel !
Looks like we can do this

export default
  computed: {
    ...mapActions
        increment : counter.actions.increment,
        set       : counter.actions.set,
        fetchCount: counter.actions.fetchCount
  }

But not this

export default
  computed:
    ...mapActions
        increment : counter.actions.increment,
        set       : counter.actions.set,
        fetchCount: counter.actions.fetchCount

[YamiOdymel]

@chabib I asked about this in jashkenas/coffeescript#4449

Keyless property requires explicit braces - {}.

[coffeescriptbot]

Migrated to jashkenas/coffeescript#4959