export declare type ExternalSubjectSynchronize = (cb: () => void) => void;
export declare type ExternalSubjectSubscribe = (handler: () => void) => void | undefined | (() => void);
export declare type ExternalSubjectShouldUpdate<T> = (a: T, b: T) => boolean;
export interface ExternalSubjectOptions<T> {
    read: () => T;
    subscribe?: ExternalSubjectSubscribe;
    shouldUpdate?: ExternalSubjectShouldUpdate<T>;
    lazySubscribe?: boolean;
}
export interface UpdateRequest {
    promise: Promise<void>;
    alive: boolean;
}
export interface ExternalSubject<T> {
    /**
     * Reads the latest value
     */
    getCurrentValue: () => T;
    /**
     * Reads the latest validated value
     */
    getCachedValue: () => T;
    /**
     * Gets the ongoing validation request
     */
    getRequest: () => UpdateRequest | undefined;
    requestUpdate: () => void;
    /**
     * Used for comparing the values
     */
    shouldUpdate: ExternalSubjectShouldUpdate<T>;
    subscribe: ExternalSubjectSubscribe;
    setSynchronizer: (sync: ExternalSubjectSynchronize) => void;
    destroy: () => void;
}