这段代码是否描述了C#中的存在类型?

explanation question 我只是想知道这是否是一种在C中构造它的方法:

public abstract class SomeExistentialType
{
    private SomeExistentialType() { }


    public abstract int Foo();

    public ExistentialType Create()
    {
        return new ConcreteType1();
    }

    private class ConcreteType1: SomeExistentialType
    {
        public override int Foo()
        {
            //some implementation...
        }
    }

    private class ConcreteType1: SomeExistentialType
    {
        public override int Foo()
        {
            //some implementation...
        }
    }

    private class ConcreteType1: SomeExistentialType
    {
        public override int Foo()
        {
            //some implementation...
        }
    }
}