import { Observable } from 'rxjs/internal/Observable';
import { Subject } from 'rxjs/internal/Subject';
import { BehaviorSubject } from 'rxjs/internal/BehaviorSubject';
/**
 * Returns `true` if a given observable has a next() method.
 * @param subject$
 */
export declare function hasNext<T>(subject$: Observable<T> | Subject<T> | BehaviorSubject<T>): subject$ is Subject<T> | BehaviorSubject<T>;
/**
 * Gets initial value if the root observable is a behavior subject (as this will emit synchronously)
 * @param observable$
 */
export declare const UNSET_VALUE: {};
export declare function initialObservableValue<T>(observable$: Observable<T>): T | {};
/**
 * `useRxState`
 *
 * Returns current value and a callback to change it by mutating a given subject.
 * Returns only current value in case of Observable.
 *
 * Example:
 * const [name, setName] = useRxState(name$)
 * where name$ could be new BehaviorSubject('None');
 *
 * setName('Alice') under the hood will call name$.next('Alice')
 *
 * @param subject$
 */
export declare function useRxState<S extends Observable<any> | Subject<any> | BehaviorSubject<any>>(subject$: S): S extends BehaviorSubject<infer T> ? [T, (value: T) => void] : S extends Subject<infer T> ? [T | undefined, (value: T) => void] : S extends Observable<infer T> ? [T | undefined] : never;
/**
 * `useRxStateResult`
 *
 * For a given observable returns a current value.
 *
 * Example:
 * const name = useRxStateResult(name$)
 *
 * @param observable$
 */
export declare function useRxStateResult<T>(observable$: Observable<T>): T | undefined;
/**
 * `useRxStateAction`
 *
 * For a given subject returns a set function.
 *
 * Example:
 * const setName = useRxStateResult(name$);
 */
export declare function useRxStateAction<T>(subject$: Subject<T>): (value: T) => void;