I prefer to use the abstract IList interface in my public APIs, rather than passing around concrete List implementations. However, the one thing I’ve always missed was the awesome .ForEach syntax which was available on the List implementation.

Today, I realized that I can use extension methods to add methods to interfaces.

public static class ListExtensions
{
    public static void ForEach<T>(this IList<T> source, Action<T> action)
    {
        foreach (T item in source)
            action(item);
    }
}

This now allows me to do things like:

public static void Main(string[] args)
{
    IList<string> items = GetItems();
    items.ForEach(Console.WriteLine);
}
 
private static IList<string> GetItems()
{
    return new List<string> { "abc", "123" };
}

I much prefer this syntax to the foreach construct.