/**
 * state.ts
 *
 * @package  vrkd/object
 * @author  Fernando Salazar
 */
import { type Obj } from "./objectTypes";
export declare const StateSym: unique symbol;
export type Subscriber<S> = (state: S) => void;
/**
 * Interactions with state produces new object, promoting immutability.
 */
export declare class State<S extends Obj> {
    /**
     * Never access the state directly.
     */
    private [StateSym];
    private _subscriber;
    /**
     * Store constructor
     *
     * @param {object} $state
     * @param {object} $default version of state.
     */
    constructor($state: S, $default?: S | null);
    /**
     * Merge a state into current state.
     *
     * @param {object} $state
     */
    setState($state: Partial<S>): void;
    /**
     * Always produce a copy of the state.
     *
     * @return The current state cloned.
     */
    getState(): S;
    /**
     * Subscriber will fire with the latest state after each state change.
     *
     * @param subscriber
     */
    subscribe(subscriber: Subscriber<S>): void;
    /**
     * Read a state param without cloning the param.
     *
     * @param  {string} $name
     * @return  Param value
     */
    protected _readStateParam($name: keyof S): S[keyof S];
}