Visibility of variables in struct nested within a class

[Charles Hixson]

I have a class that defines a variable (root).  Within it I have nested 
a struct.  If I refer to that variable within the struct I get the message:
cbt2.d(760): Error: this for root needs to be type BTree not type Path

If I change the struct to a class, the error goes away, but I'd prefer 
to use a struct.

My computer is a 64bit Linux system with
DMD64 D Compiler v2.063

The particular statement referenced is:
             if    (root is null)
though there are many others.

Is this the way things are supposed to happen?  (Changing the struct to 
a class is an OK patch, but I don't understand why it should either work 
or be necessary.)

-- 
Charles Hixson