Tuple generic

tuple-utils.ts

export namespace TupleUtils {
  /**
   * Get type of first element
   * @example `First<[0, 1, 2]>` → `0`
   */
  export type First<Tuple extends [any, ...any[]]> = Tuple[0]

  /**
   * Get type of last element
   * @example `Last<[0, 1, 2]>` → `2`
   */
  export type Last<Tuple extends any[]> = utils.Last<Tuple>

  /**
   * Add an element to the end of a tuple
   * @example `Append<[0, 1, 2], 'new'>` → `[0, 1, 2, 'new']`
   */
  export type Append<Tuple extends any[], Addend> = Reverse<Prepend<Reverse<Tuple>, Addend>>

  /**
   * Add an element to the beginning of a tuple
   * @example `Prepend<[0, 1, 2], 'new'>` → `['new', 0, 1, 2]`
   */
  export type Prepend<Tuple extends any[], Addend> = utils.Prepend<Tuple, Addend>

  /**
   * Reverse a tuple
   * @example `Reverse<[0, 1, 2]>` → `[2, 1, 0]`
   */
  export type Reverse<Tuple extends any[]> = utils.Reverse<Tuple>

  export namespace utils {
    export type Last<Tuple extends any[], Default = never> = {
      0: Default,
      1: Tuple extends [infer SoleElement] ? SoleElement : never,
      2: ((..._: Tuple) => any) extends ((_: any, ..._1: infer Next) => any) ? Last<Next> : Default
    }[
      Tuple extends [] ? 0 : Tuple extends [any] ? 1 : 2
    ]

    export type Prepend<Tuple extends any[], Addend> =
      ((_: Addend, ..._1: Tuple) => any) extends ((..._: infer Result) => any) ? Result : never

    export type Reverse<Tuple extends any[], Prefix extends any[] = []> = {
      0: Prefix,
      1: ((..._: Tuple) => any) extends ((_: infer First, ..._1: infer Next) => any)
        ? Reverse<Next, Prepend<Prefix, First>>
        : never
    }[
      Tuple extends [any, ...any[]] ? 1 : 0
    ]
  }
}