Why do the wrapper objects use abstract classes instead of interfaces?

[tacosontitan]

Currently, all three of the wrapper files contain abstract definitions and a corresponding implementation such as:

public abstract class SampleWrapper {
    public abstract void HelloWorld();
}
public class SampleWrapperImpl : SampleWrapper {
    public override void HelloWorld() =>
        Console.WriteLine("Hello world!");
}

This could have been an interface and default implementation instead such as:

public interface ISampleWrapper {
    void HelloWorld();
}
public class SampleWrapper : ISampleWrapper {
    public void HelloWorld() =>
        Console.WriteLine("Hello world!");
}

What was the driving factor to use an abstract class over an interface when no partial implementations were provided?

[jbogard]

Those wrapper classes are there to bridge the generics divide. That's all.