In some of the previous posts on delegates we defined a custom delegate. Instead of creating a custom delegate we could use one of the delegates that come with .NET framework. We have Action<> and Func<>.

Action<>

Instead of creating a custom delegate we could one of the existing delegates that come with .NET framework. We have two delegates that are generic: Action<> and Func<>.. Func<> points to a method that returns a value, whereas Action<> points to one that does not.

namespace Photos
{
    class PhotoProcessor
    {
        
        // Remove our delegate and use Action<Photo> instead
        //public delegate void PhotoFilterHandler(Photo photo);
        
        public void Process(string path, Action<Photo> filterHandler)
        {
            var photo = Photo.Load(path);

            filterHandler(photo);

            photo.Save();
        }
    }
}

    class Program
    {
        static void Main(string[] args)
        {
            var myVar = new PhotoProcessor();
            var filters = new PhotoFilters();
            //PhotoProcessor.PhotoFilterHandler filterHandler = filters.ApplyContrast;
            Action<Photo> filterHandler = filters.ApplyContrast;  // remove above line
            // below we add another pointer
            filterHandler += filters.ApplyBrightness;
            filterHandler += RemoveRedEyeFilter;
            myVar.Process("pic.jpg", filterHandler);
        }
        static void RemoveRedEyeFilter (Photo photo)
        {
            Console.WriteLine("Remove Red Eye was added here by the consumer!");
        }
    }

Alternative: Interfaces

For flexibility, an alternative is interfaces. How do we decide which one to use?