What are Delegates? How do you use them?

• A Delegate is a type which can help passing a function as a parameter - similar to pointer functions.
• These are derived from the Delegate class in .NET and are sealed types.
• The type of the delegate is determined by the name of the delegate.
• Methods passed into the delegate type must have the same signature as the defined delegate type.
• There are three steps:
  1. Declare a delegate type
  2. Instigate the type by associating with a method definition
  3. Invoke it
• Since the instantiated delegate is an object, it can be passed as a parameter, or assigned to a property. This allows a method to accept a delegate as a parameter, and call the delegate at some later time. This is known as an asynchronous callback, and is a common method of notifying a caller when a long process has completed.

void StartingPoint() 
{
     CallDelegate("HipHop", d1);
     CallDelegate("HipHop", d2);
}

// call the passed Del reference 
// with the passed parameter
void CallDelegate(string str, Del d)
{
    // Step 3: Calling the delegate
    d(str);
}

// Step1: declare a delegate type Del 
delegate void Del(string str);

// Step 2: Instigation
Del d1 = delegate (string str)
{
    Console.WriteLine($"Hello {str}");
};

// Step 2: Instigation
Del d2 = str =>
{
    Console.WriteLine($"Hello there! {str} via a Lambda Expression.");
};

Output:
Hello HipHop
Hello there! HipHop via a Lambda Expression.