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Conditional type doesn't work inside tuple #40067
Description
TypeScript Version: 4.1.0-dev.20200807
Search Terms: conditional type tuple
Code
type Tuple<T> = [T extends null ? T? : T];Expected behavior:
Expected the definition to work as expected.
Actual behavior:
Got the following error:
JSDoc types can only be used inside documentation comments.
Playground Link: Playground Link
Related Issues: Did not find anything close.
Activity
jack-williams commentedon Aug 15, 2020
As per #24897, outside of JSDoc the
?modifier is only valid for tuple elements, not arbitrary types. It does not make sense to say that a type can be omitted, only that an element can be omitted.ienzam commentedon Aug 18, 2020
The above definition is inside a tuple, and one way to look at that is the element can be omitted or not.
But I guess that messes up in other ways like making sure all the other elements are optional too.
typescript-bot commentedon Sep 5, 2020
This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.