tapandinto.cs

public static class Exts
{
    public static T Tap<T>(this T that, Action<T> action)
    {
        action(that);
        return that;
    }

    public static TOut Into<TIn, TOut>(this TIn that, Func<TIn, TOut> func)
    {
        return func(that);
    }
}

public class TestExts
{
    public string Logging()
    {
        return "hello".Tap(v => Console.WriteLine("DoStuff: " + v));
    }

    public string Waterfall()
    {
        return "hello".Into(v => v + " ")
                      .Into(v => v + "world")
                      .Into(v => v.ToUpper())
                      .Into(v => v + "!");
    }
}