/**
 * 递归拉平数组
 * @param list 数组
 * @returns 数组
 *
 * @example
 *
 * flat([[[1, 2, 3], 4], 5])
 *
 * // [1, 2, 3, 4, 5]
 */
export declare function flat<T>(list: readonly T[]): T[];
/**
 * 拉平数组，不会递归处理
 * @param {Array<Object>} list - 对象数组
 * @param {string} key - 对象的key
 * @returns {object} 拉平后的对象
 *
 * @example
 *
 * const list = [{id: 1, name: 'a'}, {id: 2, name: 'b'}]
 *
 * flatten(list, 'id')
 *
 * // {1: {id: 1, name: 'a'}, 2: {id: 2, name: 'b'}}
 *
 */
export declare function flatten<T extends Record<string, unknown>, K extends keyof T>(list: T[], key: K): Record<string | number | symbol, T>;