How can I create an IList Employee list based on my Employee class?

Question

I'm trying to create an IList<Employee> list based on my Employee class (below).  But this is erroring out.  Is my employee class missing anything?  How could I make this work?
private void EmployeeList()
IList<Employee> arL = new IList<Employee>(); //<<<<----errors out here
arL.Add(new Employee {Name="Mary",Gender="Female", Age=35});
arL.Add(new Employee { Name = "Bob", Gender = "Male", Age = 40 });
arL.Add(new Employee { Name = "Tom", Gender = "Male", Age = 50 });
var qm = from Employee employee in arL
where employee.Age < 50
select employee;
foreach (var m in arL)
Console.WriteLine(m.ToString());
class Employee
private string name;
private string gender;
private int age;
public string Name
get { return name; }
set { name = value; }
public string Gender
get { return gender; }
set { gender = value; }
public int Age
get {return age;}
set {age = value;}
Rich P

Answer 1

IList is an interface, not a class. This means that it can't be instantiated (can't be "newed").
List is a class, so it can be instantiated. It implements the IList interface, which means that it must provide the functionality specified in that interface.
That's what an interface is - a definition of functionality that a class must provide. An interface is often described as a contract that a class must fulfill.
So in the code in your last post, you are saying that arL is an instance of some class that implements the IList interface, and you are then setting it to an instance of the class List. The List class implements the IList interface, so this assignment is
legit. It would also be legit to use any other class that implements IList, such as an array.
Any class that implements IList can have as much extra functionality as whoever wrote it likes, as long as it implements at least the functionality of the interface.
Sometimes you will come across a method in a library over which you have no control and which returns IList rather than list. In such a case you will be forced to do something like...
IList list = SomeMethodOrOther();
So you will have no idea what class list is an instance of, but you will know that it has the functionality of IList. This is about the only circumstance where I would recommend defining a variable as IList rather than List (but it probably won't be long
before there are some replies to this post that disagree).