How would you teach C# delegate to a newbie?

Question

I was reviewing Andrew Troelsen book on C# 4.0. The part that explains delegates starts as smooth as:

public class SimpleMath
{
    //declare delegate
    public delegate int BinaryOp(int x, int y);

    public static int Add(int x, int y){
    return x + y;
}

class Program
{
    static void Main(string[] args){
    //create delegate which points to Add method
    BinaryOp b = new BinaryOp(SimpleMath.Add);

    //Invoke Add method using delegate
    Console.WriteLine("10 + 10 is {0}", b(10,10));
    Console.ReadLine();
}

than gets as complicated as

public class Car
{
    public int CurrentSpeed {get;set;}
    public int MaxSpeed {get;set;}
    private bool carIsDead {get;set;}
    public Car() {MaxSpeed=10;}
    public Car(int maxSpeed, int currentSpeed)
    {
        MaxSpeed = maxSpeed;
        CurrentSpeed = currentSpeed;
    }
    //declare delegate
    public delegate void CarEngineHandler(string msgForCaller);
    //define member of this delegate
    private CarEngineHandler listOfHandlers;
    //add registration function for the caller
    public void RegisterWithCarEngine(CarEngineHandler methodToCall)
    {
        listOfHandlers = methodToCall;
    }

    public void Accelerate(int delta)
    {
            if (carIsDead)
            {
                    if (listOfHandlers!=null)
                            listOfHandlers("Sorry, the car is dead");
            }
            else {
                    CurrentSpeed+=delta;
                    if (10== (MaxSpeed - CurrentSpeed) && listOfHandlers!=null)
                    {
                            listOfHandlers("Gonna blow!");
                    }
                    if (CurrentSpeed >= MaxSpeed)
                            carIsDead = true;
                    else
                            Console.WriteLine("Current Speed = {0}", CurrentSpeed);
            }
    }
}

If we try to pick that content and teach somebody else, we are going to find a hard time, since it becomes tricky.

How would you teach C# delegates in a way he/she is able to understand clearly when to use them?

Answer 1

for C++ devs : delegates are like function pointers, but as objects with type check

for Java devs: delegates are interfaces with only one method

Answer 2

A common strategy for teaching any technique is, at first describe some problem which is quite hard to solve or insolvable without the technique. Then introduce the technique solving the problem in a elegant easier way. It can be applied to delegates also.

A very common use of delegate is to map a function with other variables. You can use a dictionary with integer or string keys and delegates to show the functionality. But before that give the problem to the learners to solve in their way. If you can show that your implementation is easier, you are done.

And if anyone came from C/C++ and knows about function pointers, you can just tell them 'delegate' is the C# version of function-pointers.

Answer 3

Delegate to him to teach you and then fill in the blanks.

this is far better as it motivates him to pick up an ability of "self learning" which is essential for programming.

Answer 4

I think the name delegate and the whole terminology around it is a little strange.

Basically, delegates are first class functions, i.e. functions, that are values in every sense. A simple language like JavaScript should help illustrating what this means within a short time.
That knowledge can then be translated to C# delegates and lambdas.