import type { Arr, Element, ElementNotUndefined } from '@toolbox-ts/types/defs/array';
/**
 * Returns the element at the specified index of an array, `undefined` if out of bounds, or `fallbackIfUndefined` if undefined.
 *
 * @example
 * ```ts
 * at([1, 2, 3], 1) // 2
 * at([1, 2, 3], -1) // 3
 * at([1, 2, 3], 5) // undefined
 * at([1, 2, 3], 5, null) // null
 * ```
 */
export declare const at: <T extends Arr = Arr, F = undefined>(arr: T, index: number, fallbackIfUndefined?: F) => Exclude<Element<T>, undefined> | F;
/**
 * Returns the element at the specified index of an array.
 *
 * @throws `Error` if the index is out of bounds.
 *
 * @example
 * ```ts
 * atOrThrow([1, 2, 3], 1) // 2
 * atOrThrow([1, 2, 3], -1) // 3
 * atOrThrow([1, 2, 3], 5) // throws Error
 * ```
 */
export declare const atOrThrow: <T extends Arr>(arr: T, index: number) => ElementNotUndefined<T>;
/**
 * Returns the last index of an array, -1 if empty.
 *
 * @example
 * ```ts
 * lastIndex([1, 2, 3]) // 2
 * lastIndex([]) // -1
 * ```
 */
export declare const lastIndex: <T extends Arr>(arr: T) => number;
/**
 * Returns the last element of an array, or undefined if empty.
 * @example
 * ```ts
 * last([1, 2, 3]) // 3
 * last([]) // undefined
 * ```
 */
export declare const last: <T extends Arr>(arr: T) => Element<T>;
/**
 * Returns the last element of an array.
 *
 * @throws `Error` if the array is empty.
 * @example
 * ```ts
 * lastOrThrow([1, 2, 3]) // 3
 * lastOrThrow([]) // throws Error
 * ```
 */
export declare const lastOrThrow: <T extends Arr>(arr: T) => ElementNotUndefined<T>;
/**
 * Returns the first element of an array, or undefined if empty.
 *
 * @example
 * ```ts
 * first([1, 2, 3]) // 1
 * first([]) // undefined
 * ```
 */
export declare const first: <T extends Arr>(arr: T) => Element<T>;
/**
 * Returns the first element of an array.
 *
 * @throws `Error` if the array is empty.
 *
 * @example
 * ```ts
 * firstOrThrow([1, 2, 3]) // 1
 * firstOrThrow([]) // throws Error
 * ```
 */
export declare const firstOrThrow: <T extends Arr = Arr>(arr: T) => ElementNotUndefined<T>;