Re: Class variables or class singleton variables?

I don't get what you mean. The singleton class of a class is obviously 
not the same as the class itself, so getting different object IDs was to 
be expected.

Maybe you mean something different? If you wonder why I open the 
singleton class in the original class with "self" instead of outside the 
class with the name: That's both the same, but the first approach is 
less redundant and (in my opinion) more readable. But you should 
actually use "send".

And again: You cannot define a class instance variable for Foo in the 
singleton class of Foo. Those are two different variables:

class Foo
  @x = 'Foo'
  class << self    # or class << Foo
    @x = 'singleton'
  end
end

[Foo, Foo.singleton_class].each do |c|
  puts "#{c}: @x == #{c.instance_variable_get :@x}"
end

An instance variable always belongs to a specific object instance (hence 
the name). So if you define @x within the body of the singleton class, 
it will actually belong to the singleton class and not the original 
class.

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