TypeScript 3.9 | Advanced Types: Extracts a tuple's last entry

Last.ts

type Head<T extends any[]> = T extends [any, ...any[]] ? T[0] : never
type HasTail<T extends any[]> = T extends [] | [any] ? false : true
type Tail<T extends any[]> = ((...t: T) => any) extends (
  _: any,
  ...tail: infer TT
) => any
  ? TT
  : []

type Last<T extends any[]> = {
  0: Last<Tail<T>>
  1: Head<T>
}[HasTail<T> extends true ? 0 : 1]

type LastEntry = Last<[1, 2, 3, 4]> // 4

// https://medium.com/free-code-camp/typescript-curry-ramda-types-f747e99744ab
// https://github.com/millsp/medium/blob/master/types-curry-ramda/src/index.ts