import { IEmitOptions, IEventOptions, ISubscriber, SubEvent } from './event';
/**
 * Represents a change in the number of subscriptions, as used with {@link SubEventCount.onCount} event.
 */
export interface ISubCountChange {
    /**
     * New number of subscriptions.
     */
    newCount: number;
    /**
     * Previous number of subscriptions.
     */
    prevCount: number;
}
/**
 * Constructor options for {@link SubEventCount} class.
 */
export interface ICountOptions<T> extends IEventOptions<T> {
    /**
     * Emit options for event {@link SubEventCount.onCount}.
     */
    emitOptions?: IEmitOptions;
}
/**
 * Extends {@link SubEvent} with event {@link onCount}, to observe the number of subscriptions.
 */
export declare class SubEventCount<T = unknown> extends SubEvent<T> {
    /**
     * @hidden
     */
    protected _notify: (data: ISubCountChange) => SubEvent<ISubCountChange>;
    /**
     * Triggered on any change in the number of subscriptions.
     * @event onCount
     */
    readonly onCount: SubEvent<ISubCountChange>;
    /**
     * Event constructor.
     *
     * @param options
     * Configuration Options.
     */
    constructor(options?: ICountOptions<T>);
    /**
     * Cancels all existing subscriptions for the event.
     *
     * It overrides the base implementation, to trigger event {@link onCount}
     * when there was at least one subscription.
     *
     * @returns
     * Number of subscriptions cancelled.
     *
     * @see {@link Subscription.cancel}
     */
    cancelAll(): number;
    /**
     * Overrides base implementation, to trigger event {@link onCount} during
     * `subscribe` and `cancel` calls.
     *
     * @hidden
     */
    protected _createCancel(sub: ISubscriber<T>): () => void;
}