#391 – Passing a Delegate Instance as a Parameter

When you use the delegate keyword to define a delegate, you’re actually defining a new class, which inherits from System.MulticastDelegate.

        public delegate string StringProcessorDelegate(string input);

When you declare a variable of this delegate type and assign a method to it, you’re creating an instance of the new class.

            StringProcessorDelegate stringProcessor = ReverseAndHighLight;

        static string ReverseAndHighLight(string input)
        {
            // Reverse, add asterisks
        }

You now have a delegate instance that is set up to invoke the ReverseAndHighlight method.  This instance is actually just a normal .NET object, since it’s an instance of the new type that derives from System.MulticastDelegate.  This means that you can pass this object to a method, as a parameter.

            string result = DoStringProcessing(stringProcessor, "Basil Rathbone");

        static string DoStringProcessing(StringProcessorDelegate del, string input)
        {
            Console.WriteLine("Input string: {0}", input);
            string result = del(input);
            Console.WriteLine("Result: {0}", result);

            return result;
        }