Nested Class Constructor Accessibility

I wanted to share this very nice, small, creative piece of code that I've stumbled upon while looking for different perspectives on the subject.

The problem at hand is, let us say, that you have a Class, a "Parent" or "Container" class, and you want this class to have the ability to instantiate other classes.
This is a very real and sometimes serious situation, where access to constructor is forbidden to everyone and everything except one controlling object.

One "usual" pattern is using a factory builder. however, usually you will be able to either access the constructor still, or accessing the factory method from almost everywhere.

There are a few good solutions out there involving interfaces. The only downside to them is that they require quite a bit of code to be written down, for such a simple functionality.

And to be honest, what are we asking for???
To have a class with a nested class that only the containing class can access!

http://stackoverflow.com/questions/1664793/how-to-restrict-access-to-nested-class-member-to-enclosing-class

Here you can see different implementations that deal with this problem.
Check out Ray Burns' answer: Answer

public class Journal
{
  private static Func<object, JournalEntry> _newJournalEntry;

  public class JournalEntry
  {
    static JournalEntry()
    {
      _newJournalEntry = (object) => new JournalEntry(object);
    }
    private JournalEntry(object value)
    {
      ...

Here we can see, that in the nested class's static constructor we initialize a delegate to our true nested class's constructor, this is a private static field in the containing class, so it can only be accesses within the containing class.

Thus, in this example, JournalEntry can only be instantiated by functionality that has to be implemented inside the Journal object.

It might seem trivial to some, and might seem complex to others, I must admit I never thought of attacking the subject in this fashion, and it is quite creative.
Kudos.