我可以阻止一个类被非抽象对象继承吗？

Question

Consider the following classes:

public abstract class Planet
{
    protected abstract Material Composition { get; }
}

public abstract class TerrestrialPlanet : Planet
{
    protected override Material Composition
    {
        get
        {
            return Type.Rocky;
        }
    }
}
public abstract class GasGiant : Planet
{
    protected override Material Composition
    {
        get
        {
            return Type.Gaseous;
        }
    }
}

Is there a way to prevent a non-abstract object from inheriting directly from class Planet ?

In other words, can we enforce that any class that directly inherits from Planet be abstract?

// ok, because it doesn't directly inherit from Planet
public class Earth : TerrestrialPlanet { ... }

// ok, because it is abstract
public abstract class IcyPlanet : Planet { ... }

// we want to prevent this
public class Pluto : Planet { ... }

Answer 1

No, you cannot prevent a non-abstract class from inheriting a given public class that you create.

If all of the classes deriving from the base will be in the same assembly, and none of the concrete classes will, you could make the base class internal , to avoid exposing it externally at all , which would prevent other assemblies from extending it directly. If it needs to be exposed publicly, or the concrete implementations will be in the same assembly, then this of course isn't an option.