Michael:

You will find that your new Metaclass ("m,") although it has a
MethodDictionary and a superclass, does not have the right MethodDictionary
or superclass to actually create any instances.  That's why the code in
ClassBuilder does the following:

privateNewSubclassOf: newSuper
	"Create a new meta and non-meta subclass of newSuper"
	"WARNING: This method does not preserve the superclass/subclass
invariant!"
	| newSuperMeta newMeta |
	newSuperMeta := newSuper ifNil:[Class] ifNotNil:[newSuper class].
	newMeta := Metaclass new.
	newMeta
		superclass: newSuperMeta
		methodDictionary: MethodDictionary new
		format: newSuperMeta format.
	^newMeta new

If you provided the new Metaclass with a MethodDictionary with the right
CompiledMethods in it, you wouldn't need to give it a superclass.  But the
usual practice is to make the superclass of a Metaclass instance be either
Class (which is an instance of an instance of Metaclass) or else some other
already-provisioned Metaclass instance.

Be forewarned: You're dealing with the "moebius strip" of Smalltalk's
class-metaclass metamodel, and it's easy to get yourself very confused.
Careful thought will be required to avoid error.

Note: The class of Metaclass is 'Metaclass class,' and the class of
'Metaclass class' is Metaclass. This provides the transitive closure of
Smalltalk's metamodel.  The superclass of a root class is nil, the
superclass of the metaclass of a root class should normally be Class, so
that the instance of the metaclass instance (a root class) will inherit
"Class behavior" from Class itself.

--Alan

-----Original Message-----
From: squeak-dev-bounces at lists.squeakfoundation.org
[mailto:squeak-dev-bounces at lists.squeakfoundation.org] On Behalf Of Michael
van der Gulik
Sent: Sunday, March 19, 2006 1:35 PM
To: squeak-dev at lists.squeakfoundation.org
Subject: Metaclass issues.

Hi all.

I've found myself in the unfortunate position of needing to work with
Metaclasses for my own project!

I'll spare the details; you can email me directly if you want them :-).
Why does the following happen?:

m := Metaclass new. " Construct the Metaclass instance for my new class"
c := m new. "Make my new class".

The code will evaluate fine, but if you try to do anything with c, CPU usage
hits 100% and I can't seem to break out of it.

Ideas? I suspect it is something like m not being initialised properly with
a superclass etc. I'm taking my inspiration from
ClassBuilder>>privateNewSubclassOf:.

Michael.