I prefer to use the abstract IList<T> interface in my public APIs, rather than passing around concrete List<T> implementations. However, the one thing I’ve always missed was the awesome .ForEach syntax which was available on the List<T> 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.