Why does the following doesn't compile? (involves generics and inheritance in c#)

Question

This compiles:

    class ReplicatedBaseType
    {
    }

    class NewType: ReplicatedBaseType
    {
    }

    class Document
    {
    ReplicatedBas         


        

Answer 1

Variance exists in C# 4.0 targetting .NET 4), but is limited to interfaces and usage of in/out (oh, and arrays of reference-types). For example, to make a covariant sequence:

class DalBase : IEnumerable where T: ReplicatedBaseType
{
    public IEnumerator GetEnumerator() {throw new NotImplementedException();}
    IEnumerator IEnumerable.GetEnumerator() { throw new NotImplementedException(); }
}

class DocumentTemplate
{
    IEnumerable BaseCollection;
    DocumentTemplate()
    {
        BaseCollection = new DalBase(); // Error in this line. It seems this is not possible
    }
}

But other than that... no. Stick to either non-generic lists (IList), or use the expected list type.