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Type Iterator#next() argument (yield expression) #32998
Description
Search Terms
Iterator.next() type, yield expression type
Suggestion
Type Iterator.next()/yield. I suggest Iterator<A, B>, where A is the input type, and B is the output type.
Mentioned in #10148 and #14883.
Required by #32283.
Alternative proposal in #32523, those this requires more drastic changes to TypeScript's type model.
Use Cases
Pretty self-explanatory; I want typed expressions. It's why I use TypeScript.
And currently, all yield ... expressions have no typing. (They are typed as any).
Examples
function* totalLength() {
let result = 0;
while (true) {
result += (yield result).length;
}
const t = totalLength();
t.next('abc'); // 0
t.next('def'); // 3
t.return(''); // 6Checklist
My suggestion meets these guidelines:
- This wouldn't be a breaking change in existing TypeScript/JavaScript code
- This wouldn't change the runtime behavior of existing JavaScript code
- This could be implemented without emitting different JS based on the types of the expressions
- This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
- This feature would agree with the rest of TypeScript's Design Goals.
Activity
pauldraper commentedon Aug 21, 2019
And actually, Iterator has additional problems, like
return?(value?: any): IteratorResult<T>which is just simply wrong.To be more concrete, the types should be
The optional argument is problematic for having non-undefined values inside the generator, but I don't have a better suggestion.
AlCalzone commentedon Aug 21, 2019
I think you should take a look at the TS 3.6 release notes
https://devblogs.microsoft.com/typescript/announcing-typescript-3-6-rc/
RyanCavanaugh commentedon Aug 21, 2019
See #30790 and its linked issues
typescript-bot commentedon Aug 23, 2019
This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.
pauldraper commentedon Aug 24, 2019
Excellent, thanks AlCalzone for linking to the 3.6 RC notes.
TypeScript Bot (@typescript-bot) I think you might not be working correctly (you didn't actually close).