import { IDStr } from "./Strings";
export declare type OnErrorCallback = (err: Error) => void;
export declare type OnNextCallback<V> = (value: V | undefined) => void;
export declare type SnapshotUnsubscriber = () => void;
export declare type SnapshotSubscriberFactory<V> = () => SnapshotSubscriber<V>;
export declare type SnapshotSubscriber<V> = (onNext: OnNextCallback<V>, onError?: OnErrorCallback) => SnapshotUnsubscriber;
export interface SnapshotSubscriberWithID<V> {
    readonly id: IDStr;
    readonly subscribe: SnapshotSubscriber<V>;
}
export interface SubscriptionValue<T> {
    readonly value: T | undefined;
    readonly error: Error | undefined;
}
export declare type SnapshotTuple<T> = [T | undefined, Error | undefined];
export declare function NULL_SNAPSHOT_SUBSCRIBER<V>(onNext: OnNextCallback<V>, onError?: OnErrorCallback): () => void;
export declare type SnapshotConverter<F, T> = (from: F | undefined) => T | undefined;
export declare namespace SnapshotSubscribers {
    function converted<F, T>(subscriber: SnapshotSubscriber<F>, converter: SnapshotConverter<F, T>): SnapshotSubscriber<T>;
    function of<V>(value: V): SnapshotSubscriber<V>;
}