export type Observer<T = any> = (value: Readonly<T>) => void;
export interface Observable<T = any> {
    close: () => void;
    listen(observer: Observer<T>): Unsubscription;
    next(value: T): void;
    subscribe(observer: Observer<T>): Unsubscription;
    readonly value: T;
}
export declare function observable<T>(): Observable<T | undefined>;
export declare function observable<T>(value: T): Observable<T>;