meta-class subclass relationships

Ruby exposes its singleton meta-classes, eg:

class <<B ; $Meta_B = self ; end

But their relationships are not quite what I expected. For example:

Suppose that A inherits from B (and B inherits from Object). Of course,
this means that A instances respond to all the B instance messages. So:

A.new.is_a? B -> true

At the same time, the A class object responds to all the B class object
messages. So:

class <<Object ; $Meta_Object = self ; end
class <<B ; $Meta_B = self ; end
class <<A ; $Meta_A = self ; end

A.is_a? $Meta_A -> true
B.is_a? $Meta_A -> false
A.is_a? $Meta_B -> true
B.is_a? $Meta_B -> true

Since everything that is_a $Meta_A also is_a $Meta_B, I expected a
subclass/superclass relationship. Indeed, I expected the following to
be true:

$Meta_A.superclass == $Meta_B
$Meta_B.superclass == $Meta_Object
$Meta_Object.superclass == Class
Class.superclass == Module
Module.superclass == Object
Object.superclass == nil

The above superclass chain reflects how a message to the class A object
is looked up. What surprised me is that the first two equalities above
are false.

Should they have been true?

FWIW: The superclass of both $Meta_A and $Meta_B is something called
#<Class:Class>, which is its own superclass and is a subclass of
$Meta_Object:

$X = $Meta_A.superclass -> #<Class:Class>
$X == $Meta_B.superclass -> true
$X == $X.superclass -> true
$X < $Meta_Object -> true
--
Posted via http://www.ruby-forum.com/.

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