00014-easy-first-of-array

问题

Implement a generic First<T> that takes an Array T and returns its first element's type.

For example:

type arr1 = ['a', 'b', 'c']
type arr2 = [3, 2, 1]

type head1 = First<arr1> // expected to be 'a'
type head2 = First<arr2> // expected to be 3

解答

type First<T> = T extends [infer R, ...any[]] ? R : never