Ability to skip elements in tuple type annotation

[zhuravlikjb]

Want to write something like this:

var [, a, b]: [, string, number] = [0, "a", 5];

instead of inserting 'any' manually to all the omitted positions.

[DanielRosenwasser]

If I took your example and later added x as in the following:

var [x, a, b]: [, string, number] = [0, "a", 5];

What is the desired behavior?

[zhuravlikjb]

I suppose that x here should have type of right-hand-side[0], or 'any', if the right-hand-side is absent.

Exactly the same way as for ordinary type annotations, when they are omitted:
var x = 0 => x: number
var x => x: any

The same in the case of non-destructuring declarations:

var x: [, string, number] = [0, "a", 5];     // x is [number, string, number]
var y: [, string, number];  // y is [any, string, number]

[RyanCavanaugh]

We had a question when discussing this issue -- what are the kinds of cases where the inferred type is "not correct" ? In other words, what's the value of writing these annotations vs letting them be inferred?

[RyanCavanaugh]

@zhuravlikjb any thoughts on the above question?

[zhuravlikjb]

Sorry for the delay with answer. This question is just about consistency: JavaScript allows empty items and elision in many syntax elements. If it's allowed for array literals, why not to allow it for type annotations? Nothing critical here if the existing behaviour will remain. Just a "why not" thing. :)

[RyanCavanaugh]

Doesn't seem to be a lot of desire for this in practice, plus it introduces new weird cases as Daniel pointed out.