First, let's add a method to retrieve eigenclass "copied from this blog post"
class Object
def eigenclass
class << self
self
end
end
end
Then create a simple class
class A
end
puts A.new.eigenclass.superclass # => A
puts Class.new.eigenclass.superclass # => #<Class:Object>
I was expecting the second puts to output Class
Any clue why this happened?
From that blogpost, you can construct a similar diagram:
+------------------+ +-------------------+
| Object |- eigenclass ->| Object eigenclass |
+------------------+ +-------------------+
^ ^
| superclass superclass |
+------------------+ +-------------------+
| A |- eigenclass ->| A eigenclass |
+------------------+ +-------------------+
^
| superclass
+-------+ +------------------+
| A.new |- eigenclass ->| A.new.eigenclass |
+-------+ +------------------+
Trying to find the superclass of the eigenclass of an instance of A shows that it points to the A class.
A.new.eigenclass.superclass # => A
Class.new returns an instance of a Class object, i.e. a new class. It is a class, just like the A class.
Class.new.class # => Class
A.class # => Class
A's superclass and Class.new's superclass are both implicitly Object.
Class.new.superclass # => Object
A.superclass # => Object
Because A's superclass is Object, A's eigenclass's superclass is Object's eigenclass.
Object.eigenclass # => #<Class:Object>
A.eigenclass.superclass # => #<Class:Object>
A.eigenclass.superclass == Object.eigenclass # => true
Similarly, finding the superclass of the eigenclass of Class.new yields Object's eigenclass
Class.new.eigenclass.superclass # => #<Class:Object>
The difference between Class.new and A.new is that Class.new is itself a class and so can construct new objects, while A.new cannot.
Class.new.new # => #<#<Class:0x007f86b50d8f70>:0x007f86b50d8f20>
A.new.new # => NoMethodError: undefined method `new' for #<A:0x007f86b50cbf50>