/**
 * Represents a function that handles state changes.
 * @template T The type of state being observed.
 */
export type Observer<T> = (newState: T) => void;
/**
 * Represents a function that removes an observer subscription.
 */
export type Unsubscribe = () => void;
/**
 * Interface representing an observer service for managing state and subscriptions.
 * @template T The type of the state being observed.
 */
export interface IObserverService<T> {
    /**
     * @returns {T} The current state value.
     */
    get state(): T;
    /**
     * @param {T} value The new state value to set.
     */
    set state(value: T);
    /**
     * Subscribes an observer to state changes.
     * @param {Observer<T>} observer The function to be called when state changes.
     * @returns {Unsubscribe} A function to remove the subscription.
     */
    subscribe(observer: Observer<T>): Unsubscribe;
    /**
     * Subscribes to updates from another observer service.
     * @template X Type of the observed state.
     * @param {IObserverService<X>} observer The observer service to subscribe to.
     * @param {Observer<X>} onUpdate Callback function for handling updates.
     * @returns {Unsubscribe} A function to remove the subscription.
     */
    listen<X>(observer: IObserverService<X>, onUpdate: Observer<X>): Unsubscribe;
}
/**
 * Type guard to check if an object implements the IObserverService interface.
 * @param {any} obj Object to check
 * @returns {boolean} True if the object implements IObserverService
 */
export declare function isAnObserverService(obj: any): obj is IObserverService<any>;