/** Describes index keys for any type. */
export type Key = string | number | symbol;
/** Represents a gamut of "falsy" values. */
export type Falsy = null | undefined | false | 0 | 0n | '';
/** Represents an object that is considered "empty". */
export type EmptyObject = Record<Key, null | undefined | ''>;
/** Represents a value that is considered "empty" in various contexts. */
export type EmptyLike = Falsy | Array<Falsy> | EmptyObject;
/** Represents an instantiable class `T` with constructor parameters. */
export type Class<T, Args extends unknown[] = any[]> = {
    prototype: Pick<T, keyof T>;
    new (...args: Args): T;
};
/** Returns `true` if `value` is a boolean, else `false`. */
export declare function isBoolean(value?: unknown): value is boolean;
/** Returns `true` if `value` is a class, else `false`. */
export declare function isClass<T = unknown>(value: unknown): value is Class<T>;
/**
 * Returns `true` if `value` is empty, else `false`:
 *
 * - **array:** `[]`, `[<empty values>]`.
 * - **object:** `{}`, `{ key: <null|undefined|''> }`.
 * - **string:** `''`, `'    '`.
 * - **null:** `null`.
 * - **undefined:** `undefined`.
 * - **boolean:** `false`.
 * - **integer:** `0`.
 * - **float:** `0.0`.
 */
export declare function isEmpty(value?: unknown): value is EmptyLike;
/** Returns `true` if `value` is a function, else `false`. */
export declare function isFunction(value?: unknown): value is (...args: any[]) => any;
/** Returns `true` if `value` is nullish, else `false`. */
export declare function isNil(value?: unknown): value is null | undefined;
/** Returns `true` if `value` is `null`, else `false`. */
export declare function isNull(value?: unknown): value is null;
/** Returns `true` if `value` is a number, else `false`. */
export declare function isNumber(value?: unknown): value is number;
/** Returns `true` if `value` is an object, else `false`. */
export declare function isObject(value?: unknown): value is object;
/** Returns `true` if `value` is a plain object, else `false`. */
export declare function isPlainObject(value?: unknown): value is object;
/** Returns `true` if `value` is a string, else `false`. */
export declare function isString(value?: unknown): value is string;
/** Returns `true` if `value` is a symbol, else `false`. */
export declare function isSymbol(value?: unknown): value is symbol;
/** Returns `true` if `value` is `undefined`, else `false`. */
export declare function isUndefined(value?: unknown): value is undefined;