import { NotifyPropertyChangedType } from '../../notify/notifyPropertyChangedSymbol';
import { Observable, OperatorFunction } from 'rxjs';
import { IChangeSet } from '../IChangeSet';
/**
 * Observes property changes for the specified property, starting with the current value
 * @param value The source
 * @param key The key to observe
 * @param notifyInitial If true the resulting observable includes the initial value
 * @param fallbackValue A fallback value may be specified to ensure a notification is received when a value is unobtainable.
 *           For example when observing Parent.Child.Age, if Child == null the value is unobtainable as Age is a struct and cannot be set to Null.
 *           For an object like Parent.Child.Sibling, sibling is an object so if Child == null, the value null and obtainable and is returned as null.
 */
export declare function whenPropertyChanged<TObject, TProperty extends keyof TObject>(value: NotifyPropertyChangedType<TObject>, key: TProperty, notifyInitial?: boolean, fallbackValue?: () => TObject[TProperty]): Observable<TObject[TProperty]>;
/**
 * Watches each item in the collection and notifies when any of them has changed
 * @typeparam TObject The type of the object.
 * @typeparam TKey The type of the key.
 * @typeparam TValue The type of the value.
 * @param key The key to watch
 * @param notifyInitial if set to <c>true</c> [notify on initial value].
 */
export declare function whenPropertyChanged<TObject, TProperty extends keyof TObject>(key: TProperty, notifyInitial?: boolean): OperatorFunction<IChangeSet<NotifyPropertyChangedType<TObject>, TProperty>, TObject[TProperty]>;