/**
 * A reactive wrapper for state values that supports pub/sub notifications.
 * When the value is set, all subscribers are notified with the new and old
 * values.
 */
export declare class StateValue<T> {
    protected _value: T;
    protected subscribers: Set<(newValue: T, oldValue: T) => void>;
    /**
     * Creates a new StateValue with an initial value.
     * @param initialValue The initial value for this state
     */
    constructor(initialValue: T);
    /**
     * Gets the current value.
     */
    get value(): T;
    /**
     * Sets the value and notifies all subscribers of the change.
     * @param newValue The new value to set
     */
    set value(newValue: T);
    /**
     * Updates the value using an updater function.
     * This prevents accidental mutations and enforces immutable patterns.
     * @param updater Function that receives current value and returns new value
     */
    update(updater: (current: T) => T): void;
    /**
     * Subscribes to value change notifications.
     * @param callback Function to call when value changes,
     * receives (newValue, oldValue)
     * @returns A function to unsubscribe from notifications
     */
    subscribe(callback: (newValue: T, oldValue: T) => void): () => void;
}