export declare function isKeyOf<O>(k: unknown): k is keyof O;
export declare function isObjectGuard(obj: unknown): obj is object;
export declare function isDefined(val: unknown): val is NonNullable<any>;
/**
 * @description
 * Allows to pass only keys which value is of specific type.
 *
 * @example
 *
 * interface Creature {
 *  id: number;
 *  type: string;
 *  name: string;
 * }
 *
 * const cat = {id: 1, type: 'cat', name: 'Fluffy'};
 *
 * function updateCreature<T>(creature: T, key: OnlyKeysOfSpecificType<T, string>, value: string) {
 *  // update logic
 * }
 *
 * // Valid key
 * updateCreature(cat, 'name', 'Luna');
 *
 * // Invalid key
 * updateCreature(cat, 'id', 3);
 *
 * @docsPage OnlyKeysOfSpecificType
 * @docsCategory interfaces
 */
export type OnlyKeysOfSpecificType<T, S> = {
    [Key in keyof T]: S extends T[Key] ? Key : never;
}[keyof T];