Question

Is there way to add new method to List object over the object from which it’s made of .In other word can class be written in such way ,when List is made from it that it adds new method to that List. Here’s an exemple:

class Employee
{
    public int age;
    public Employee(int age)
    {
         this.age = age;
    }
    //some more code here...
}

And then:

List<Employee> sector01 = new List<Employee>(){new Employee(22), new Employee(35)};
sector01.OutputAll(); //Adds method like this

Answer 1

You could define it as an extension method:

namespace SomeNamespace
{
    public static class ListExtensions
    {
        public static void OutputAll(this IEnumerable<Employee> employees)
        {
            foreach (var employee in employees)
            {
                Console.WriteLine("{0}: {1}", employee.FirstName, employee.LastName);
            }
        }
    }
}

and then simply bring the namespace where this static class is defined into scope:

using SomeNamespace;

and now you will be able to do this:

List<Employee> sector01 = new List<Employee>()
{
    new Employee(22), 
    new Employee(35)
};
sector01.OutputAll();