@typedly/array/lib/insert.type.d.ts

A TypeScript type definitions package to handle array-related operations.

/**
 * @description Inserts the `Element` type to the generic type variable `Array` at index of `Index` type.
 * @export
 * @template {readonly Type[]} Array
 * @template {Type} Element
 * @template {number} Index
 * @template [Type=any]
 * @template {readonly Type[]} [Accumulator=[]]
 * @example
 * import { Insert } from '@typedly/array';
 *
 * // Insert 99 at index 2 in the array [1, 2, 3, 4]
 * type Example1 = Insert<[1, 2, 3, 4], 99, 2>;  // [1, 2, 99, 3, 4]
 * const example1: Example1 = [1, 2, 99, 3, 4];
 *
 * // Insert 'a' at index 1 in the array ['b', 'c']
 * type Example2 = Insert<['b', 'c'], 'a', 1>;  // ['b', 'a', 'c']
 * const example2: Example2 = ['b', 'a', 'c'];
 *
 * // Insert 'X' at index 0 in an empty array
 * type Example3 = Insert<[], 'X', 0>;  // ['X']
 * const example3: Example3 = ['X'];
 */
export type Insert<Array extends readonly Type[], Element extends Type, Index extends number, Type = any, Accumulator extends readonly Type[] = []> = Accumulator['length'] extends Index ? [...Accumulator, Element, ...Array] : Array extends [infer First, ...infer Rest extends readonly Type[]] ? Insert<Rest, Element, Index, Type, [...Accumulator, First] extends readonly Type[] ? [...Accumulator, First] : never> : Accumulator;