/// <summary>
/// Produces the set union of two sequences by using a specified <see cref="T:System.Collections.Generic.IEqualityComparer`1"/>.
/// </summary>
/// <typeparam name="TSource">The type of the elements of the input sequences.</typeparam>
/// <param name="first">An <see cref="IBindableCollection{TElement}"/> whose distinct elements form the first set for the union.</param>
/// <param name="second">An <see cref="IBindableCollection{TElement}"/> whose distinct elements form the second set for the union.</param>
/// <param name="comparer">The <see cref="T:System.Collections.Generic.IEqualityComparer`1"/> to compare values.</param>
/// <returns>
/// An <see cref="IBindableCollection{TElement}"/> that contains the elements from both input sequences, excluding duplicates.
/// </returns>
/// <exception cref="T:System.ArgumentNullException">
/// <paramref name="first"/> or <paramref name="second"/> is null.</exception>
public static IBindableCollection <TSource> Union <TSource>(this IBindableCollection <TSource> first, IBindableCollection <TSource> second, IEqualityComparer <TSource> comparer) where TSource : class
{
return(first.Union(second).Distinct(comparer));
}