C#: Delegate
What is Delegate?
A delegate is a type safe function pointer. That is, it holds a reference (pointer) to a function.
The signature of the delegate must match the signature of the function the delegate points to, otherwise you get a compiler error. This is a reason delgates are called as type safe function pointers.
A delegate is similar to a class. You can create an instance of it, and when you do so, you pass in the function name as a parameter to the delegate consturctor, and it is to this function the delegate will point to.
Tip to remember delegate syntax: Delegates syntax look very much similar to a method with a delegate keyword.
// A delegate just a type safe function pointer. Using delegate gives developers a lot of flexibilites
namespace Delegates
{
// delegate function
public delegate void HelloFunctionDelegate(string message);
class Program
{
// method
static void Hello(string message)
{
Console.WriteLine(message);
}
// Entry point
static void Main(string[] args)
{
// Instantiate delegate
// Signature must match the method
HelloFunctionDelegate del = new HelloFunctionDelegate(Hello);
del("Hello from delegates"); // output: Hello from delegates
}
}
}
Delegate Usage Example
namespace Delegate_Demo
{
// Delegate function
public delegate bool IsPromotable(Employee emp);
// Employee class
class Employee
{
public int ID { get; set; }
public string Name { get; set; }
public int Salary { get; set; }
public int Experience { get; set; }
public static void Promote(List<employee> empList, IsPromotable IsEligibleToPromote)
{
foreach (var employee in empList)
{
if (IsEligibleToPromote(employee))
{
Console.WriteLine(employeeList.Name + " promoted");
}
}
}
}
class Program
{
static void Main(string[] args)
{
Employee employee = new Employee
{
new Employee() { ID = 101, Name = "John", Salary = 50000, Experience = 5 },
new Employee() { ID = 102, Name = "Mary", Salary = 40000, Experience = 4 },
new Employee() { ID = 103, Name = "Jose", Salary = 30000, Experience = 3 }
};
Employee.Promote(employee, emp => emp.Experience >= 5);
}
}
}