Split & Concat Types w/ Delimiter

split-concat.ts

/*
 * Note: This is just for fun.
 */

type Split<T extends string, Delimiter extends string = ""> =
  "" extends T
    ? []   
    : T extends `${infer Head}${Delimiter}${infer Tail}`
      ? [Head, ...Split<Tail, Delimiter>]
      : [T];

type Concat<T extends string[], Delimiter extends string = ""> = 
  T extends [infer Head extends string, ...infer Tail extends string[]]
    ? `${Head}${Delimiter}${Concat<Tail>}`
    : "";


type S0 = Split<"">;  // []
type C0 = Concat<S0>; // ""

type S1 = Split<"", "X">;  // []
type C1 = Concat<S1, "X">; // ""

type S2 = Split<"X">; // ["X"]
type C2 = Concat<S2>; // "X"

type S3 = Split<"X", "X">; // [""]
type C3 = Concat<S3, "X">; // "X"

type S4 = Split<"Hello world", " ">; // ["Hello", "world"]
type C4 = Concat<S4, " ">;           // "Hello world"

type S5 = Split<"CR#7">; // ["C", "R", "#", "7"]
type C5 = Concat<S5>;    // "CR#7"

type S6 = Split<"CR#7", "#">; // ["CR", "7"]
type C6 = Concat<S6, "#">;    // "CR#7"