set.values().next() has wrong type

[sdegutis]

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

Happens in both versions 4.2.3 and 4.3.0-beta

⏯ Playground Link

Playground link with relevant code

💻 Code

const s = new Set<string>();
s.values().next().value;

🙁 Actual behavior

Type of value is any.

🙂 Expected behavior

Type of value should probably be string | undefined or something.

[nmain]

next() returns a discriminated union so you can get what you want:

const v = s.values().next();
if (v.done) {
  v.value; // any
} else {
  v.value; // string
}

It would make more sense for v.value to be typed as void or undefined in the done case though.

[MartinJohns]

@nmain Or never.

[RyanCavanaugh]

@rbuckton I believe we have a duplicate of this?

[nmain]

Ahh yes, this seems to be #33353
Search terms: iteratorresult return