Conditional type doesn't work inside tuple

[ienzam]

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.

[jack-williams]

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]

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]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.