Why can't I use a compatible concrete type when implementing an interface

Question

I would like to be able to do something like this :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Test
{
          


        

Answer 1

Although List implements IEnumerable that's not the way interfaces work. The interface specifies exactly which types need to be exposed for properties. If you created a generic interface like

public interface IFoo where T : IEnumerable
{
    T integers { get; set; }
}

You could then use IFoo> to implement it in the way you expect.