LinqExtensions.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace System.Linq
{
    public static class LinqExtensions
    {
        public static IEnumerable<T> Flatten<T>(this IEnumerable<T> e, Func<T, IEnumerable<T>> f)
        {
            return e.SelectMany(c => f(c).Flatten(f)).Concat(e);
        }

        public static void ForEach<T>(this IEnumerable<T> collection, Action<T> action)
        {
            foreach (var item in collection)
            {
                action(item);
            }
        }

        public static ObservableCollection<T> ToObservableCollection<T>(this IEnumerable<T> collection)
        {
            return new ObservableCollection<T>(collection);
        }
    }
}