/// <summary>
/// Observe collection element's property.
/// </summary>
/// <typeparam name="TElement">Type of element</typeparam>
/// <typeparam name="TProperty">Type of property</typeparam>
/// <param name="source">Data source</param>
/// <param name="propertySelector">Property selection expression</param>
/// <param name="isPushCurrentValueAtFirst">Push current value on first subscribe</param>
/// <returns>Property sequence</returns>
public static IObservable <PropertyPack <TElement, TProperty> > ObserveElementProperty <TElement, TProperty>(this IFilteredReadOnlyObservableCollection <TElement> source, Expression <Func <TElement, TProperty> > propertySelector, bool isPushCurrentValueAtFirst = true)
where TElement : class, INotifyPropertyChanged =>
CollectionUtilities.ObserveElementProperty(source, propertySelector, isPushCurrentValueAtFirst);