Refer: Medium - Last of Array

Describe

Implement a generic Last<T> that takes an Array T and returns its last element.

For example

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

type tail1 = Last<arr1> // expected to be 'c'
type tail2 = Last<arr2> // expected to be 1

Test Cases

code snippetCopytypescript
import { Equal, Expect } from '@type-challenges/utils'

type cases = [Expect<Equal<Last<[3, 2, 1]>, 1>>, Expect<Equal<Last<[() => 123, { a: string }]>, { a: string }>>]

Solution

code snippetCopytypescript
// my solution (It may be a little complicated 🤣)
type Last<T extends any[]> = T extends [infer P, ...infer K]
  ? K['length'] extends 1
    ? K[0]
    : K['length'] extends 0
    ? P
    : Last<K>
  : never

// other solution (In js, rest element must be last element!)
type Last<T extends any[]> = T extends [...infer _, infer Z] ? Z : never