Repository navigation
Tuple type not inferred when calling generic function #6310
Description
Tuple types aren't always inferred when calling generic functions. For example:
function identity<A>(value: A): A {
return value
}
// works
const [a1, b1]: [number, string] = [1, 'a']
// works
const [a2, b2]: [number, string] = identity<[number, string]>([1, 'a'])
// breaks
const [a3, b3]: [number, string] = identity([1, 'a'])
Output:
foo.ts(12,7): error TS2322: Type '(number | string)[]' is not assignable to type '[number, string]'.
Property '0' is missing in type '(number | string)[]'.
Activity
DanielRosenwasser commentedon Jan 2, 2016
This is because the array expression needs to be contextually typed by a tuple-like type so that we can infer your type argument as a tuple. You've enforced that when you explicitly gave a type argument, but not in the last example.
One way you could achieve what you want is to add a tuple-like constraint for your type parameter:
zpdDG4gta8XKpMCd commentedon Jan 4, 2016
that's the most interesting
identifyfunction I've seen so far