“Interface not implemented” when Returning Derived Type

Question

The following code:

public interface ISomeData
{
    IEnumerable Data { get; }
}

public class MyData : ISomeData
{
    private List

        

Answer 1

What if you accessed your MyData object trough the ISomeData interface? In that case, IEnumerable could be of an underlying type not assignable to a List.

IEnumerable iss = null;

List ss = iss; //compiler error

EDIT:

I understand what you mean from your comments.

Anyway, what I would do in your case would be:

    public interface ISomeData where T: IEnumerable
    {
        T Data { get; }
    }

    public class MyData : ISomeData>
    {
        private List m_MyData = new List();
        public List Data { get { return m_MyData; } }
    }

Converting to generic Interface with appropriate constraint offers I think the best of both flexibility and readability.