Last of Array

In this medium-level challenge, you'll implement a generic Last<T> that extracts the type of the last element from an array.

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

// Video Solution: https://youtube.com/watch?v=bbXU3lF9w4Q

/* _____________ Your Code Here _____________ */

type Last<T extends any[]> = any

/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '../helpers'

type cases = [
  Expect<Equal<Last<[]>, never>>,
  Expect<Equal<Last<[2]>, 2>>,
  Expect<Equal<Last<[3, 2, 1]>, 1>>,
  Expect<Equal<Last<[() => 123, { a: string }]>, { a: string }>>,
]

Detailed Explanation

type Last<T extends unknown[]> = T extends [...infer _Rest, infer Last]
  ? Last
  : never

How it works:

• First we constrain the type T to be an array with extends unknown[]
• T extends [...infer _Rest, infer Last] matches the array type and captures the last element's type
• ? Last returns the last element's type if the array is not empty
• we return never if the array is empty

This challenge helps you understand array type operations and how to apply this concept in real-world scenarios.