Covariance in C# generic class

Question

C# 4.0 .NET 4.5 Silverlight 5 It seems weird that I cant find the solution so need some help please.

I have base class Base and derived class Child : Base. I have also h

Answer 1

I think this is what you're after:

public class Base where T : EntityObject
{
    protected Helper helper;
}
public class Child : Base
{
    public Child()
    {
        helper = new Helper();
    }
}

Edit (in response to your edit): You can add a Base, use like so:

public class Base
{
    // put anything here that doesn't rely on the type of T
    // if you need things here that would rely on T, use EntityObject and have 
    // your subclasses provide new implementations using the more specific type
}
public class Base : Base where T : EntityObject
{
    protected Helper helper;
}
public class Child : Base
{
    public Child()
    {
        helper = new Helper();
    }
}
public class User
{
    private Base myBase;
    public User(TypeEnum t)
    {
        if(t == TypeEnum.MyEntity) myBase = new Child();
        ...