@lou.codes/types/dist/HeadAndTail.d.ts

🏷️ Lou's Code shared types

import type { ArrayLike } from "./ArrayLike.js";
import type { EmptyArray } from "./EmptyArray.js";
import type { EmptyString } from "./EmptyString.js";
import type { Maybe } from "./Maybe.js";
/**
 * Get a couple with the head and tail types of an `ArrayLike`.
 *
 * @category Array
 * @category String
 * @remarks
 * Given a type argument (an `ArrayLike`), this returns a couple with the type
 * of the item in index `0` first, and the rest of the `ArrayLike` after.
 * @example
 * ```typescript
 * const array = ["🟢", "🟩", "💚"];
 * const headAndTail: HeadAndTail<typeof array> = ["🟢", ["🟩", "💚"]];
 * ```
 * @see {@link ArrayLike}
 * @see {@link EmptyArray}
 * @see {@link EmptyString}
 * @see {@link Head}
 * @see {@link Maybe}
 * @see {@link Tail}
 *
 * @template Input Input `ArrayLike`.
 */
export type HeadAndTail<Input extends ArrayLike> =
	Input extends readonly [head: infer HeadItem, ...tail: infer TailItems] ?
		readonly [head: HeadItem, tail: TailItems]
	: Input extends `${infer FirstCharacter}${infer RestOfString}` ?
		readonly [head: FirstCharacter, tail: RestOfString]
	: Input extends EmptyArray | EmptyString ?
		readonly [head: undefined, tail: Input]
	:	readonly [head: Maybe<Input[number]>, tail: Input];